Lactate dehydrogenase: Difference between revisions

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{{protein
{{enzyme
| Name = lactate dehydrogenase A
| Name = Lactate dehydrogenase
| caption =  
| EC_number = 1.1.1.27
| image =  
| CAS_number = 9001-60-9
| width =  
| GO_code = 0004459
| image = 1i10.jpg
| width = 270
| caption = Lactate dehydrogenase M tetramer (LDH5), Human
}}
 
'''Lactate dehydrogenase''' ('''LDH''' or '''LD''') is an [[enzyme]] found in nearly all living cells (animals, plants, and [[prokaryote]]s). LDH catalyzes the conversion of [[lactic acid|lactate]] to [[pyruvic acid]] and back, as it converts NAD<sup>+</sup> to  [[NADH]] and back. A [[dehydrogenase]] is an enzyme that transfers a hydride from one molecule to another.
 
LDH exist in four distinct enzyme classes. This article is specifically about the NAD(P)-dependent L-lactate dehydrogenase. Other LDHs  act on D-lactate and/or are dependent on [[cytochrome c]]: [[D-lactate dehydrogenase (cytochrome)]]) and  L-lactate ([[L-lactate dehydrogenase (cytochrome)]]).
LDH is expressed extensively in body tissues, such as blood cells and heart muscle. Because it is released during tissue damage, it is a marker of common injuries and disease such as heart failure.
 
== Reaction ==
 
[[File:Reaction catalyzed by lactate dehydrogenase.png|thumb|Reaction catalyzed by lactate dehydrogenase]]
 
[[File:Lactate dehydrogenase mechanism.png|thumb|upright=2.0|Arrow pushing mechanism for the reaction catalyzed by lactate dehydrogenase]]
 
Lactate dehydrogenase catalyzes the interconversion of [[pyruvate]] and [[lactic acid|lactate]] with concomitant interconversion of NADH and [[Nicotinamide adenine dinucleotide|NAD<sup>+</sup>]]. It converts pyruvate, the final product of [[glycolysis]], to lactate when oxygen is absent or in short supply, and it performs the reverse reaction during the [[Cori cycle]] in the [[liver]]. At high concentrations of lactate, the enzyme exhibits feedback inhibition, and the rate of conversion of pyruvate to lactate is decreased. It also catalyzes the dehydrogenation of [[2-Hydroxybutyrate]], but it is a much poorer substrate than lactate.
 
== Active site ==
 
LDH in humans uses His(193) as the proton acceptor, and works in unison with the coenzyme (Arg99 and Asn138), and substrate (Arg106; Arg169; Thr248) binding residues.<ref>{{cite journal | vauthors = Holmes RS, Goldberg E | title = Computational analyses of mammalian lactate dehydrogenases: human, mouse, opossum and platypus LDHs | journal = Computational Biology and Chemistry | volume = 33 | issue = 5 | pages = 379–85 | date = Oct 2009 | pmid = 19679512 | pmc = 2777655 | doi = 10.1016/j.compbiolchem.2009.07.006 }}</ref> The His(193) active site, is not only found in the human form of LDH, but is found in many different animals, showing the convergent evolution of LDH. The two different subunits of LDH: LDHA also known as the M subunit of LDH, and LDHB also known as the H subunit of LDH both retain the same active site, and the same amino acids participating in the reaction. The noticeable difference between the two subunits that make up LDH's tertiary structure is the replacement of alanine (in the M chain) with a glutamine (in the H chain). This tiny but notable change is believed to be the reason the H subunit can bind faster, and the M subunit's catalytic activity isn't reduced when subjected to the same conditions as the H subunit; while the H subunits activity is reduced fivefold.<ref>{{cite journal | vauthors = Eventoff W, Rossmann MG, Taylor SS, Torff HJ, Meyer H, Keil W, Kiltz HH | title = Structural adaptations of lactate dehydrogenase isozymes | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 74 | issue = 7 | pages = 2677–81 | date = Jul 1977 | pmid = 197516 | doi =  10.1073/pnas.74.7.2677| url = http://www.pnas.org/content/74/7/2677.full.pdf | pmc=431242}}</ref>
 
== Isozymes ==
 
Lactate dehydrogenase is composed of four subunits (tetramer). The two most common subunits are the LDH-M and LDH-H protein, encoded by the ''LDHA'' and ''LDHB'' genes, respectively. These two subunits can form five possible tetramers (isoenzymes): 4H, 4M, and the three mixed tetramers (3H1M, 2H2M, 1H3M). These five isoforms are enzymatically similar but show different tissue distribution: The major isoenzymes of skeletal muscle and liver, M<sub>4</sub>, has four muscle (M) subunits, while H<sub>4</sub> is the main isoenzymes for heart muscle in most species, containing four heart (H) subunits.
 
* LDH-1 (4H)—in the [[heart]] and in RBC ([[red blood cells]]), as well as the [[brain]].
* LDH-2 (3H1M)—in the [[reticuloendothelial system]]
* LDH-3 (2H2M)—in the [[lung]]s
* LDH-4 (1H3M)—in the [[kidney]]s, [[placenta]], and [[pancreas]]
* LDH-5 (4M)—in the [[liver]] and [[striated muscle]]<ref>{{cite book | last1 = Van Eerd | first1 = J. P. F. M. | last2 = Kreutzer | first2 = E. K. J. | name-list-format = vanc | title = Klinische Chemie voor Analisten deel 2 |pages=138–139 |year=1996 |isbn=978-90-313-2003-5}}</ref>
 
Usually LDH-2 is the predominant form in the [[Blood serum|serum]]. A LDH-1 level higher than the LDH-2 level (a "flipped pattern") suggests [[myocardial infarction]] (damage to heart tissues releases heart LDH, which is rich in LDH-1, into the bloodstream). The use of this phenomenon to diagnose infarction has been largely superseded by the use of [[Troponin]] I or T measurement.{{Citation needed|date=October 2013}}
 
There are two more mammalian LDH subunits that can be included in LDH tetramers: LDHC and LDHBx. LDHC is a testes-specific LDH protein, that is encoded by the LDHC gene. LDHBx is a [[peroxisome]]-specific LDH protein. LDHBx is the readthrough-form of LDHB. LDHBx is generated by [[translation]] of the LDHB [[mRNA]], but the [[stop codon]] is interpreted as an [[amino acid]]-encoding [[codon]]. In consequence, [[translation]] continues to the next stop codon. This leads to the addition of seven amino acid acids to the normal LDH-H protein. The extension contains a [[peroxisomal targeting signal]], so that LDHBx is imported into the peroxisome.<ref name="pmid25247702">{{cite journal | vauthors = Schueren F, Lingner T, George R, Hofhuis J, Gartner J, Thoms S | title = Peroxisomal lactate dehydrogenase is generated by translational readthrough in mammals | journal = eLife | volume = 3 | pages = e03640 | date = 2014 | pmid = 25247702 | doi = 10.7554/eLife.03640 | pmc=4359377}}</ref>
 
{{col-begin|width=auto}}
{{col-break}}
{{infobox protein
| Name = [[LDHA|lactate dehydrogenase A]]<br />(subunit M)
| image = Lactate dehydrogenase M4 (muscle) 1I10.png
| caption = Human lactate dehydrogenase M<sub>4</sub> (the [[isoenzyme]] found in [[skeletal muscle]]). From {{PDB|1I10}}.
| HGNCid = 6535
| HGNCid = 6535
| Symbol = LDHA
| Symbol = [[LDHA]]
| AltSymbols =  
| AltSymbols = LDHM
| EntrezGene = 3939
| EntrezGene = 3939
| OMIM = 150000
| OMIM = 150000
Line 18: Line 61:
| LocusSupplementaryData =  
| LocusSupplementaryData =  
}}
}}
{{protein
{{col-break}}
| Name = lactate dehydrogenase B
{{infobox protein
| caption =  
| Name = lactate dehydrogenase B<br />(subunit H)
| image =  
| image = Lactate Dehydrogenase B.png
| width =
| caption = Crystal structure of B-lactate dehydrogenase. From {{PDB|1T2F}}.
| HGNCid = 6541
| HGNCid = 6541
| Symbol = LDHB
| Symbol = LDHB
| AltSymbols =  
| AltSymbols = LDHL
| EntrezGene = 3945
| EntrezGene = 3945
| OMIM = 150100
| OMIM = 150100
Line 37: Line 80:
| LocusSupplementaryData =  
| LocusSupplementaryData =  
}}
}}
{{protein
{{col-break}}
{{infobox protein
| Name = lactate dehydrogenase C
| Name = lactate dehydrogenase C
| caption =  
| image = Lactate Dehydrogenase C.png
| image =  
| caption = Crystal structure of C-lactate dehydrogenase. From {{PDB|2LDX}}.
| width =  
| width =  
| HGNCid = 6544
| HGNCid = 6544
Line 56: Line 100:
| LocusSupplementaryData =  
| LocusSupplementaryData =  
}}
}}
{{SI}}
{{CMG}}


{{col-end}}
==Protein families==
{{col-begin|width=auto}}
{{col-break}}
{{Infobox protein family
| Symbol = Lact-deh-memb
| Name = D-lactate dehydrogenase, membrane binding
| image = PDB 1f0x EBI.jpg
| width =
| caption = crystal structure of d-lactate dehydrogenase, a peripheral membrane respiratory enzyme.
| Pfam = PF09330
| Pfam_clan = CL0277
| InterPro = IPR015409
| SMART =
| PROSITE =
| MEROPS =
| SCOP = 1f0x
| TCDB =
| OPM family =
| OPM protein =
| CAZy =
| CDD =
}}
{{col-break}}
{{Infobox protein family
| Symbol = Ldh_1_N
| Name =  lactate/malate dehydrogenase, NAD binding domain
| image =
| width =
| caption =
| Pfam = PF00056
| Pfam_clan = CL0063
| InterPro = IPR001236
| SMART =
| PROSITE =
| MEROPS =
| SCOP = 6ldh
| TCDB =
| OPM family =
| OPM protein =
| CAZy =
| CDD =
}}
{{col-break}}
{{Infobox protein family
| Symbol = Ldh_1_C
| Name = lactate/malate dehydrogenase, alpha/beta C-terminal domain
| image =
| width =
| caption =
| Pfam = PF02866
| Pfam_clan = CL0341
| InterPro = IPR022383
| SMART =
| PROSITE = PDOC00066
| MEROPS =
| SCOP = 6ldh
| TCDB =
| OPM family =
| OPM protein =
| CAZy =
| CDD =
}}
{{col-end}}
The family also contains L-lactate dehydrogenases that catalyse the conversion of [[L-lactate]] to [[pyruvate]], the last step in anaerobic glycolysis. Malate dehydrogenases that catalyse the interconversion of malate to oxaloacetate and participate in the citric acid cycle, and [[L-2-hydroxyisocaproate dehydrogenases]] are also members of the family. The [[N-terminus]] is a Rossmann NAD-binding fold and the [[C-terminus]] is an unusual alpha+beta fold.<ref name="pmid10075524">{{cite journal | vauthors = Chapman AD, Cortés A, Dafforn TR, Clarke AR, Brady RL | title = Structural basis of substrate specificity in malate dehydrogenases: crystal structure of a ternary complex of porcine cytoplasmic malate dehydrogenase, alpha-ketomalonate and tetrahydoNAD. | journal = J Mol Biol | volume = 285 | issue = 2 | pages = 703–12 | year = 1999 | pmid = 10075524 | pmc =  | doi = 10.1006/jmbi.1998.2357 | url = https://www.ncbi.nlm.nih.gov/pubmed/10075524 }}</ref><ref name="pmid12029364">{{cite journal | vauthors = Madern D | title = Molecular evolution within the L-malate and L-lactate dehydrogenase super-family. | journal = J Mol Evol | volume = 54 | issue = 6 | pages = 825–40 | year = 2002 | pmid = 12029364 | pmc =  | doi = 10.1007/s00239-001-0088-8 | url = https://www.ncbi.nlm.nih.gov/pubmed/12029364 }}</ref>


== Interactive pathway map ==


==Overview==
{{GlycolysisGluconeogenesis_WP534|highlight=Lactate_dehydrogenase}}
'''Lactate dehydrogenase''' ('''LDH''') is an [[enzyme]] ({{EC_number|1.1.1.27}}) present in a wide variety of organisms, including plants and animals.


==Reactions==
== Enzyme regulation ==
It catalyses the interconversion of [[pyruvate]] and [[lactic acid|lactate]] with concomitant interconversion of NADH and [[Nicotinamide adenine dinucleotide|NAD<sup>+</sup>]].  At high concentrations of lactate, the enzyme exhibits feedback inhibition and the rate of conversion of pyruvate to lactate is decreased.


[[Image:LDH_reaction.png|center|thumb|355px|Catalytic function of LDH]]
This protein may use the [[morpheein]] model of [[allosteric regulation]].<ref name="pmid22182754">{{cite journal | vauthors = Selwood T, Jaffe EK | title = Dynamic dissociating homo-oligomers and the control of protein function | journal = Arch. Biochem. Biophys. | volume = 519 | issue = 2 | pages = 131–43 | date = March 2012 | pmid = 22182754 | pmc = 3298769 | doi = 10.1016/j.abb.2011.11.020 }}</ref>


It also catalyzes the dehydrogenation of [[2-Hydroxybutyrate]], but it is a much poorer substrate than lactate.  There is little to no activity with [[beta-hydroxybutyrate]].
=== Ethanol-induced hypoglycemia ===


== Enzyme isoforms ==
Ethanol is dehydrogenated to acetaldehyde by alcohol dehydrogenase, and further into acetic acid by acetaldehyde dehydrogenase. During this reaction 2 NADH are produced. If large amounts of ethanol are present, then large amounts of NADH are produced, leading to a depletion of NAD<sup>+</sup>. Thus, the conversion of pyruvate to lactate is increased due to the associated regeneration of NAD<sup>+</sup>. Therefore, anion-gap metabolic acidosis (lactic acidosis) may ensue in ethanol poisoning.
* LDH-1 (4H) - in the [[heart]]
* LDH-2 (3H1M) - in the [[reticuloendothelial system]]
* LDH-3 (2H2M) - in the [[lung]]s
* LDH-4 (1H3M) - in the [[kidney]]s
* LDH-5 (4M) - in the [[liver]] and [[striated muscle]]


The five isozymes that are usually described in the literature each contain four subunits. The major isozymes of skeletal muscle and liver, M<sub>4</sub>, has four muscle (M) subunits; while H (heart)<sub>4</sub> is the main isozymes for heart muscle in most species, containing 4 H subunits. The other variants contain both types of subunits.
The increased NADH/NAD+ ratio also can cause hypoglycemia in an (otherwise) fasting individual who has been drinking and is dependent on gluconeogenesis to maintain blood glucose levels. Alanine and lactate  are major gluconeogenic precursors that enter gluconeogenesis as pyruvate. The high NADH/NAD+ ratio shifts the lactate dehydrogenase equilibrium to lactate, so that less pyruvate can be formed and, therefore, gluconeogenesis is impaired.


Usually LDH-2 is the predominant form in the [[serum]].  A LDH-1 level higher than the LDH-2 level (a "flipped pattern"), suggests  [[myocardial infarction]] (damage to heart tissues releases heart LDH, which is rich in LDH-1, into the bloodstream).  The use of this phenomenon to diagnose infarction has been largely superseded by the use of [[Troponin]] I or T measurement.
=== Substrate regulation ===


==Genetics in Humans==
LDH is also regulated by the relative concentrations of its substrates.  LDH becomes more active under periods of extreme muscular output due to an increase in substrates for the LDH reaction.  When skeletal muscles are pushed to produce high levels of power, the demand for ATP in regards to aerobic ATP supply leads to an accumulation of free ADP, AMP, and Pi.  The subsequent glycolytic flux, specifically production of NADH and pyruvate, exceeds the capacity for pyruvate dehydrogenase and other shuttle enzymes to metabolize pyruvate.  The flux through LDH increases in response to increased levels of pyruvate and NADH to metabolize pyruvate into lactate.<ref name="pmid10776894">{{cite journal | vauthors = Spriet LL, Howlett RA, Heigenhauser GJ | title = An enzymatic approach to lactate production in human skeletal muscle during exercise. | journal = Med Sci Sports Exerc | volume = 32 | issue = 4 | pages = 756–63 | year = 2000 | pmid = 10776894 | pmc =  | doi = 10.1097/00005768-200004000-00007 }}</ref>
 
=== Transcriptional regulation ===
 
LDH undergoes transcriptional regulation by PGC-1α.  PGC-1α regulates LDH by decreasing LDH A mRNA transcription and the enzymatic activity of pyruvate to lactate conversion.<ref name="pmid23650363">{{cite journal | vauthors = Summermatter S, Santos G, Pérez-Schindler J, Handschin C | title = Skeletal muscle PGC-1α controls whole-body lactate homeostasis through estrogen-related receptor α-dependent activation of LDH B and repression of LDH A. | journal = Proc Natl Acad Sci U S A | volume = 110 | issue = 21 | pages = 8738–43 | year = 2013 | pmid = 23650363 | pmc = 3666691 | doi = 10.1073/pnas.1212976110 }}</ref>
 
== Genetics ==
The M and H subunits are encoded by two different [[gene]]s:
The M and H subunits are encoded by two different [[gene]]s:
* The M subunit is encoded by ''LDHA'', located on [[chromosome]] 11p15.4 ({{OMIM|150000}})
* The M subunit is encoded by ''LDHA'', located on [[chromosome 11]]p15.4 ({{OMIM|150000}})
* The H subunit is encoded by ''LDHB'', located on chromosome 12p12.2-p12.1 ({{OMIM|150100}})
* The H subunit is encoded by ''LDHB'', located on chromosome 12p12.2-p12.1 ({{OMIM|150100}})
* A third isoform, ''LDHC'' or ''LDHX'', is expressed only in the [[testis]] ({{OMIM|150150}}); its gene is likely a duplicate of ''LDHA'' and is also located on the eleventh chromosome (11p15.5-p15.3)
* A third isoform, ''LDHC'' or ''LDHX'', is expressed only in the [[testis]] ({{OMIM|150150}}); its gene is likely a duplicate of ''LDHA'' and is also located on the eleventh chromosome (11p15.5-p15.3)
* The fourth isoform is localized in the [[peroxisome]]. It is tetramer containing one LDHBx subunit, which is also encoded by ''LDHB'' gene. The LDHBx protein is seven amino acids longer than the LDHB (LDH-H) protein. This amino acid extension is generated by functional translational readthrough.<ref name="pmid25247702"/>
Mutations of the M subunit have been linked to the rare disease ''exertional [[myoglobinuria]]'' (see OMIM article), and mutations of the H subunit have been described but do not appear to lead to disease.
=== Mutations ===
[[File:Mutated_LDH-5.png|thumb|This is a mutant version of the LDH-5 enzyme, which is usually found in skeletal muscle]]
In rare cases, a mutation in the genes controlling the production of lactate dehydrogenase will lead to a medical condition known as lactate dehydrogenase deficiency. Depending on which gene carries the mutation, one of two types will occur: either lactate dehydrogenase-A deficiency (also known as glycogen storage disease XI) or lactate dehydrogenase-B deficiency. Both of these conditions affect how the body breaks down sugars, primarily in certain muscle cells. Lactate dehydrogenase-A deficiency is caused by a mutation to the [[LDHA]] gene, while lactate dehydrogenase-B deficiency is caused by a mutation to the LDHB gene.<ref>{{cite web | url = https://ghr.nlm.nih.gov/condition/lactate-dehydrogenase-deficiency | title = Lactate dehydrogenase deficiency | date = 2016-02-29 | website = Genetics Home Reference
| access-date = 2016-03-02 }}</ref>
This condition is inherited in an autosomal recessive pattern, meaning that both parents must contribute a mutated gene in order for this condition to be expressed.<ref>{{cite web | url = https://www.mda.org/disease/metabolic-diseases-of-muscle/causes-inheritance | title = Diseases - Metabolic Diseases - Causes/Inheritance | website = Muscular Dystrophy Association | access-date = 2016-03-02 }}</ref>
A complete lactate dehydrogenase enzyme consists of four [[protein subunit]]s.<ref>{{cite journal | vauthors = Millar DB, Frattali V, Willick GE | title = The quaternary structure of lactate dehydrogenase. I. The subunit molecular weight and the reversible association at acid pH | journal = Biochemistry | volume = 8 | issue = 6 | pages = 2416–21 | date = Jun 1969 | pmid = 5816379 | doi = 10.1021/bi00834a025 }}</ref> Since the two most common subunits found in lactate dehydrogenase are encoded by the [[LDHA]] and LDHB genes, either variation of this disease causes abnormalities in many of the lactate dehydrogenase enzymes found in the body. In the case of lactate dehydrogenase-A deficiency, mutations to the LDHA gene results in the production of an abnormal lactate dehydrogenase-A subunit that cannot bind to the other subunits to form the complete [[enzyme]]. This lack of a functional subunit reduces the amount of enzyme formed, leading to an overall decrease in activity. During the anaerobic phase of [[Citric acid cycle|glycolysis]] (the [[Cori cycle|Cori Cycle]]), the mutated enzyme is unable to convert [[Pyruvic acid|pyruvate]] into lactate to produce the extra energy the cells need. Since this subunit has the highest concentration in the LDH enzymes found in the skeletal muscles (which are the primary muscles responsible for movement), high-intensity physical activity will lead to an insufficient amount of energy being produced during this anaerobic phase.<ref>{{cite journal | vauthors = Kanno T, Sudo K, Maekawa M, Nishimura Y, Ukita M, Fukutake K | title = Lactate dehydrogenase M-subunit deficiency: a new type of hereditary exertional myopathy | journal = Clinica Chimica Acta; International Journal of Clinical Chemistry | volume = 173 | issue = 1 | pages = 89–98 | date = Mar 1988 | pmid = 3383424 | doi = 10.1016/0009-8981(88)90359-2 }}</ref> This in turn will cause the muscle tissue to weaken and eventually break down, a condition known as [[rhabdomyolysis]]. The process of rhabdomyolysis also releases [[myoglobin]] into the blood, which will eventually end up in the urine and cause it to become red or brown: another condition known as [[myoglobinuria]].<ref>{{cite web | url = http://neuromuscular.wustl.edu/msys/myoglob.html | title = Myoglobinuria; Rhabdomyolysis | website = neuromuscular.wustl.edu | access-date = 2016-03-02 }}</ref> Some other common symptoms are exercise intolerance, which consists of fatigue, muscle pain, and cramps during exercise, and skin rashes.<ref>{{cite book | url = https://books.google.com/books?id=iRxvzLRYdlQC | title = Inherited Metabolic Diseases
| last = Hoffmann | first = Georg Friedrich | name-list-format = vanc | date = 2002-01-01 | publisher = Lippincott Williams & Wilkins | isbn = 9780781729000 }}</ref><ref name=":0">{{cite web | url = http://neuromuscular.wustl.edu/msys/glycogen.html#ldh | title = Glycogenoses | website = neuromuscular.wustl.edu | access-date = 2016-03-02 }}</ref> In severe cases, myoglobinuria can damage the kidneys and lead to life-threatening kidney failure.<ref>{{cite web | url = https://www.ncbi.nlm.nih.gov/gtr/conditions/C2752022/ | title = Glycogen storage disease XI - Conditions - GTR - NCBI | website = www.ncbi.nlm.nih.gov | access-date = 2016-03-02 }}</ref> In order to obtain a definitive diagnosis, a muscle biopsy may be performed to confirm low or absent LDH activity. There is currently no specific treatment for this condition.
In the case of lactate dehydrogenase-B deficiency, mutations to the LDHB gene results in the production of an abnormal lactate dehydrogenase-B subunit that cannot bind to the other subunits to form the complete enzyme. As with lactate dehydrogenase-A deficiency, this mutation reduces the overall effectiveness in the enzyme.<ref>{{cite web | url = https://ghr.nlm.nih.gov/gene/LDHB | title = LDHB gene
| date = 2016-02-29 | website = Genetics Home Reference | access-date = 2016-03-02 }}</ref> However, there are some major differences between these two cases. The first is the location where the condition manifests itself. With lactate dehydrogenase-B deficiency, the highest concentration of B subunits can be found within cardiac muscle, or the heart. Within the heart, lactate dehydrogenase plays the role of converting lactate back into pyruvate so that the pyruvate can be used again to create more energy.<ref>{{cite web | url = http://www.worthington-biochem.com/ldh/default.html | title = Lactate Dehydrogenase - Worthington Enzyme Manual | website = www.worthington-biochem.com | access-date = 2016-03-02 }}</ref> With the mutated enzyme, the overall rate of this conversion is decreased. However, unlike lactate dehydrogenase-A deficiency, this mutation does not appear to cause any symptoms or health problems linked to this condition.<ref name=":0" /><ref>{{cite web | url = http://www.omim.org/entry/614128
| title = OMIM Entry # 614128 - LACTATE DEHYDROGENASE B DEFICIENCY; LDHBD | website = www.omim.org | access-date = 2016-03-02 }}</ref> At the present moment, it is unclear why this is the case. Affected individuals are usually discovered only when routine blood tests indicate low LDH levels present within the blood.
== Role in muscular fatigue ==
The onset of acidosis during periods of intense exercise is commonly attributed to accumulation of lactic acid.  From this reasoning, the idea of lactate production being a primary cause of muscle fatigue during exercise has been widely adopted.  A closer, mechanistic analysis of lactate production under anaerobic conditions shows that there is no biochemical evidence for the production of lactate through LDH contributing to acidosis.  While LDH activity is correlated to muscle fatigue,<ref name="pmid716962">{{cite journal | vauthors = Tesch P, Sjödin B, Thorstensson A, Karlsson J | title = Muscle fatigue and its relation to lactate accumulation and LDH activity in man. | journal = Acta Physiol Scand | volume = 103 | issue = 4 | pages = 413–20 | year = 1978 | pmid = 716962 | pmc =  | doi = 10.1111/j.1748-1716.1978.tb06235.x }}</ref> the production of lactate by means of the LDH complex works as a system to delay the onset of muscle fatigue.
LDH works to prevent muscular failure and fatigue in multiple ways.  The lactate-forming reaction generates cytosolic NAD+, which feeds into the [[Glyceraldehyde 3-phosphate dehydrogenase#Overall reaction catalyzed|glyceraldehyde 3-phosphate dehydrogenase]] reaction to help maintain cytosolic redox potential and promote substrate flux through the [[Glycolysis#Pay-off phase|second phase of glycolysis]] to promote ATP generation.  This, in effect, provides more energy to contracting muscles under heavy workloads.  The production and removal of lactate from the cell also ejects a proton consumed in the LDH reaction- the removal of excess protons produced in the wake of [[Fermentation (biochemistry)#Lactic acid fermentation|this fermentation reaction]] serves to act as a buffer system for muscle acidosis.  Once proton accumulation exceeds the rate of uptake in lactate production and removal through the LDH symport,<ref name="pmid14559724">{{cite journal | vauthors = Juel C, Klarskov C, Nielsen JJ, Krustrup P, Mohr M, Bangsbo J | title = Effect of high-intensity intermittent training on lactate and H+ release from human skeletal muscle. | journal = Am J Physiol Endocrinol Metab | volume = 286 | issue = 2 | pages = E245-51 | year = 2004 | pmid = 14559724 | pmc =  | doi = 10.1152/ajpendo.00303.2003 }}</ref> muscular acidosis occurs.
== Medical relevance ==
LDH is a protein that normally appears throughout the body in [[reference ranges for blood tests#Lactate dehydrogenase|small amounts]]. Many cancers can raise LDH levels, so LDH may be used as a [[tumor marker]], but at the same time, it is not useful in identifying a specific kind of cancer. Measuring LDH levels can be helpful in monitoring treatment for cancer. Noncancerous conditions that can raise LDH levels include heart failure, hypothyroidism, anemia, pre-eclampsia,  meningitis, encephalitis, acute pancreatitis, HIV and lung or liver disease.<ref name="url_Cancer_Diagnosis_Stanford_Cancer_Center">{{cite web | url = http://cancer.stanford.edu/information/cancerDiagnosis | title = Cancer Diagnosis - Understanding Cancer | author = Stanford Cancer Center | work = Understanding Cancer | publisher =  Stanford Medicine }}</ref>


Mutations of the M subunit have been linked to the rare disease ''exertional myoglobinuria'' (see OMIM article), and mutations of the H subunit have been described but do not appear to lead to disease.
[[Tissue breakdown]] releases LDH, and therefore LDH can be measured as a surrogate for tissue breakdown, e.g. [[hemolysis]]. LDH is measured by the lactate dehydrogenase (LDH) test (also known as the LDH test or lactic acid dehydrogenase test).  Comparison of the measured LDH values with the normal range help guide diagnosis.<ref name="url_Lactate_dehydrogenase_test">{{cite web | url = https://www.nlm.nih.gov/medlineplus/ency/article/003471.htm | title = Lactate dehydrogenase test: MedlinePlus Medical Encyclopedia | author = | work = MedlinePlus | publisher = U.S. National Library of Medicine }}</ref>
 
=== Cancer cells===
 
[[File:LDH activity- normal vs canceous cells.png|thumb|Comparison of LDH activity in normal and cancerous cells|400px]]
 
LDH is involved in tumor initiation and metabolism.  Cancer cells rely on increased glycolysis resulting in increased lactate production in addition to aerobic respiration in the mitochondria, even under oxygen-sufficient conditions (a process known as the [[Warburg effect#Oncology|Warburg effect]]<ref name="pmid13298683">{{cite journal | vauthors = Warburg O | title = On the origin of cancer cells. | journal = Science | volume = 123 | issue = 3191 | pages = 309–14 | year = 1956 | pmid = 13298683 | pmc =  | doi = 10.1126/science.123.3191.309 }}</ref>).  This state of fermentative glycolysis is catalyzed by the A form of LDH.  This mechanism allows tumorous cells to convert the majority of their glucose stores into lactate regardless of oxygen availability, shifting use of glucose metabolites from simple energy production to the promotion of accelerated cell growth and replication.  For this reason, LDH A and the possibility of inhibiting its activity has been identified as a promising target in cancer treatments focused on preventing carcinogenic cells from proliferating.
 
Chemical inhibition of LDH A has demonstrated marked changes in metabolic processes and overall survival carcinoma cells.  Oxamate is a cytosolic inhibitor of LDH A that significantly decreases ATP production in tumorous cells as well as increasing production of [[reactive oxygen species]] (ROS).  These ROS drive cancer cell proliferation by activating kinases that drive cell cycle progression growth factors at low concentrations,<ref name="pmid9054359">{{cite journal | vauthors = Irani K, Xia Y, Zweier JL, Sollott SJ, Der CJ, Fearon ER, Sundaresan M, Finkel T, Goldschmidt-Clermont PJ | title = Mitogenic signaling mediated by oxidants in Ras-transformed fibroblasts. | journal = Science | volume = 275 | issue = 5306 | pages = 1649–52 | year = 1997 | pmid = 9054359 | pmc =  | doi = 10.1126/science.275.5306.1649 }}</ref> but can damage DNA through oxidative stress at higher concentrations.  Secondary lipid oxidation products can also inactivate LDH and impact its ability to regenerate NADH,<ref name="pmid24552270">{{cite journal | vauthors = Ramanathan R, Mancini RA, Suman SP, Beach CM | title = Covalent Binding of 4-Hydroxy-2-nonenal to Lactate Dehydrogenase Decreases NADH Formation and Metmyoglobin Reducing Activity. | journal = J Agric Food Chem | volume = 62 | issue = 9 | pages = 2112–7 | year = 2014 | pmid = 24552270 | doi = 10.1021/jf404900y }}</ref> directly disrupting the enzymes ability to convert lactate to pyruvate.
 
While recent studies have shown that LDH activity is not necessarily an indicator of metastatic risk,<ref name="pmid24439336">{{cite journal | vauthors = Xu HN, Kadlececk S, Profka H, Glickson JD, Rizi R, Li LZ | title = Is Higher Lactate an Indicator of Tumor Metastatic Risk? A Pilot MRS Study Using Hyperpolarized (13)C-Pyruvate. | journal = Acad Radiol | volume = 21 | issue = 2 | pages = 223–31 | year = 2014 | pmid = 24439336 | doi = 10.1016/j.acra.2013.11.014 }}</ref> LDH expression can act as a general marker in the prognosis of cancers.  Expression of LDH5 and VEGF in tumors and the stroma has been found to be a strong prognostic factor for diffuse or mixed-type gastric cancers.<ref name="pmid24401755">{{cite journal | vauthors = Kim HS, Lee HE, Yang HK, Kim WH | title = High lactate dehydrogenase 5 expression correlates with high tumoral and stromal vascular endothelial growth factor expression in gastric cancer. | journal = Pathobiology | volume = 81 | issue = 2 | pages = 78–85 | year = 2014 | pmid = 24401755 | doi = 10.1159/000357017 }}</ref>


==Medical use==
=== Hemolysis ===
=== Hemolysis ===
In [[medicine]], LDH is often used as a marker of tissue breakdown as LDH is abundant in [[red blood cell]]s and can function as a marker for [[hemolysis]]. A blood sample that has been handled incorrectly can show false-positively high levels of LDH due to [[erythrocyte]] damage.


It can also be used as a marker of [[myocardial infarction]]. Following a myocardial infarction, levels of LDH peak at 3-4 days and remain elevated for up to 10 days. In this way, elevated levels of LDH can be useful for determining if a patient has had a myocardial infarction if they come to doctors several days after an episode of chest pain.
In [[medicine]], LDH is often used as a marker of tissue breakdown as LDH is abundant in [[red blood cell]]s and can function as a marker for [[hemolysis]]. A blood sample that has been handled incorrectly can show false-positively high levels of LDH due to [[erythrocyte]] damage.
 
It can also be used as a marker of [[myocardial infarction]]. Following a myocardial infarction, levels of LDH peak at 3–4 days and remain elevated for up to 10 days. In this way, elevated levels of LDH (where the level of LDH1 is higher than that of LDH2, i.e. the LDH Flip, as normally, in serum, LDH2 is higher than LDH1) can be useful for determining whether a patient has had a myocardial infarction if they come to doctors several days after an episode of chest pain.


=== Tissue turnover ===
=== Tissue turnover ===
Other uses are assessment of [[necrosis|tissue breakdown]] in general; this is possible when there are no other indicators of [[hemolysis]]. It is used to follow-up [[cancer]] (especially [[lymphoma]]) patients, as [[cancer cell]]s have a high rate of turnover with destroyed cells leading to an elevated LDH activity.
 
Other uses are assessment of [[necrosis|tissue breakdown]] in general; this is possible when there are no other indicators of [[hemolysis]]. It is used to follow up [[cancer]] (especially [[lymphoma]]) patients, as [[cancer cell]]s have a high rate of turnover, with destroyed cells leading to an elevated LDH activity.


=== Exudates and transudates ===
=== Exudates and transudates ===
Measuring LDH in fluid aspirated from a [[pleural effusion]] (or [[pericardial effusion]]) can help in the distinction between [[exudate]]s (actively secreted fluid, e.g. due to [[inflammation]]) or [[transudate]]s (passively secreted fluid, due to a high [[hydrostatic pressure]] or a low [[oncotic pressure]]). LDH is elevated (>200 U/l) in an exudate and low in a transudate. In [[empyema]], the LDH levels generally will exceed 1000 U/l.
 
Measuring LDH in fluid aspirated from a [[pleural effusion]] (or [[pericardial effusion]]) can help in the distinction between [[exudate]]s (actively secreted fluid, e.g. due to [[inflammation]]) or [[transudate]]s (passively secreted fluid, due to a high [[hydrostatic pressure]] or a low [[oncotic pressure]]). The usual criterion (included in [[Pleural effusion#Light's criteria|Light's criteria]]) is that a ratio of fluid LDH versus upper limit of normal serum LDH of more than 0.6<ref name="Heffner">{{cite journal | vauthors = Heffner JE, Brown LK, Barbieri CA | title = Diagnostic value of tests that discriminate between exudative and transudative pleural effusions. Primary Study Investigators | journal = Chest | volume = 111 | issue = 4 | pages = 970–80 | date = April 1997 | pmid = 9106577 | doi = 10.1378/chest.111.4.970 }}</ref> or {{math|{{fraction|2|3}}}}<ref name="Light's">{{cite journal | vauthors = Light RW, Macgregor MI, Luchsinger PC, Ball WC | title = Pleural effusions: the diagnostic separation of transudates and exudates | journal = Ann. Intern. Med. | volume = 77 | issue = 4 | pages = 507–13 | date = October 1972 | pmid = 4642731 | doi = 10.7326/0003-4819-77-4-507 }}</ref> indicates an exudate, while a ratio of less indicates a transudate. Different laboratories have different values for the upper limit of serum LDH, but examples include 200<ref name=joseph2001>{{cite journal | vauthors = Joseph J, Badrinath P, Basran GS, Sahn SA | title = Is the pleural fluid transudate or exudate? A revisit of the diagnostic criteria | journal = Thorax | volume = 56 | issue = 11 | pages = 867–70 | date = November 2001 | pmid = 11641512 | pmc = 1745948 | doi = 10.1136/thorax.56.11.867 }}</ref> and 300<ref name=joseph2001/> [[International unit|IU]]/L.<ref name=Joseph2002>{{cite journal | vauthors = Joseph J, Badrinath P, Basran GS, Sahn SA | title = Is albumin gradient or fluid to serum albumin ratio better than the pleural fluid lactate dehydroginase in the diagnostic of separation of pleural effusion? | journal = BMC Pulm Med | volume = 2 | issue =  | pages = 1 | date = March 2002 | pmid = 11914151 | pmc = 101409 | doi = 10.1186/1471-2466-2-1 }}</ref> In [[empyema]], the LDH levels, in general, will exceed 1000 IU/L.


=== Meningitis and encephalitis ===
=== Meningitis and encephalitis ===
The [[enzyme]] is also found in [[cerebrospinal fluid]] where high levels of lactate dehydrogenase in cerebrospinal fluid are often associated with [[bacterium|bacteria]]l [[meningitis]]. High levels of the enzyme can also be found in cases of [[virus|viral]] meningitis, generally indicating the presence of [[encephalitis]] and poor [[prognosis]].


=== HIV and elevated LDH ===
High levels of lactate dehydrogenase in cerebrospinal fluid are often associated with [[bacterium|bacteria]]l [[meningitis]].<ref name="Stein1998">{{cite book | vauthors = Stein JH | title = Internal Medicine|url=https://books.google.com/books?id=mqg2dPYS-u0C&pg=PA1408|accessdate=12 August 2013 | year=1998 | publisher = Elsevier Health Sciences | isbn = 978-0-8151-8698-4 | pages = 1408–}}</ref> In the case of [[virus|viral]] meningitis, high LDH, in general, indicates the presence of [[encephalitis]] and poor [[prognosis]].
LDH is often measured in HIV patients as a non-specific marker for [[Pneumocystis jiroveci]] (formerly Pneumocystis carinii) pneumonia (PCP).  Elevated LDH in the setting of upper respiratory symptoms in an HIV patient suggests, but is not diagnostic for, PCP.


== Complete Differential Diagnosis of an Elevated Lactate Dehydrogenase (LDH)==
=== HIV ===
* [[Acute tubular necrosis]]
 
* [[Asparaginase Erwinia Chrysanthemi]]
LDH is often measured in HIV patients as a non-specific marker for [[Pneumocystis pneumonia|pneumonia due to ''Pneumocystis jirovecii'']] (PCP). Elevated LDH in the setting of upper respiratory symptoms in an HIV patient suggests, but is not diagnostic for, PCP. However, in HIV-positive patients with respiratory symptoms, a very high LDH level (>600 IU/L) indicated [[histoplasmosis]] (9.33 more likely) in a study of 120 PCP and 30 histoplasmosis patients.<ref name="pmid12161854">{{cite journal | vauthors = Butt AA, Michaels S, Greer D, Clark R, Kissinger P, Martin DH | title = Serum LDH level as a clue to the diagnosis of histoplasmosis | journal = AIDS Read | volume = 12 | issue = 7 | pages = 317–21 | date = July 2002 | pmid = 12161854 | doi =  }}</ref>
* Cardiac [[arrhythmia]]
 
* [[Ceftazidime]]
=== Dysgerminoma ===
* [[Cefotaxime sodium]]
 
* [[Cidofovir]]
Elevated LDH can be an early clinical sign of a rare malignant cell tumor called a [[dysgerminoma]]. Not all dysgerminomas produce LDH, and this is often a non-specific finding.
* [[Cirrhosis]]
 
* [[Congestive Heart Failure]]
== Prokaryotes ==
* [[Dermatomyositis]]
 
* [[Erythrocyte]] destruction from [[prosthetic heart valve]]
A cap-[[cell membrane|membrane]]-binding [[protein domain|domain]] is found in [[prokaryotic]] lactate dehydrogenase. This consists of a large seven-stranded [[antiparallel (biochemistry)|antiparallel]] [[beta-sheet]] flanked on both sides by [[alpha helix|alpha-helices]]. It allows for [[Cell membrane|membrane]] association.<ref name="pmid10944213">{{cite journal | vauthors = Dym O, Pratt EA, Ho C, Eisenberg D | title = The crystal structure of D-lactate dehydrogenase, a peripheral membrane respiratory enzyme | journal = Proc. Natl. Acad. Sci. U.S.A. | volume = 97 | issue = 17 | pages = 9413–8 | date = August 2000 | pmid = 10944213 | pmc = 16878 | doi = 10.1073/pnas.97.17.9413 }}</ref>
* [[Glomerulonephritis]]
* [[Hemolytic anemia]]
* [[Hepatic failure]]
* [[Hepatitis]]
* [[Hepatoma]]
* Infarction
* [[Infectious mononucleosis]]
* [[Ischemic colitis]]
* [[Kidney transplant]] rejection
* [[Leukemia]]
* [[Liver abscess]]
* [[Lymphoma]]
* [[Megaloblastic anemia]]
* [[Meropenem]]
* [[Multiple Myeloma]]
* Muscular [[trauma]]
* [[Myocardial Infarction]]
* [[Myocarditis]]
* [[Myopathy]]
* [[Neuroblastoma]]
* Neurogenic muscular atrophy
* [[Pancreatitis]]
* [[Pneumonia]]
* [[Portal hypertension]]
* Postoperative
* Progressive [[muscular dystrophy]]
* [[Pulmonary embolism]]
*[[Streptozocin]]
* [[Testicular cancer]]


== See also ==
== See also ==
* [[Oxidoreductase]]
{{Portal|Molecular and Cellular Biology|border=no}}
* [[Dehydrogenase]]
* [[Dehydrogenase]]
* [[Lactic acid|Lactate]]
* [[Oxidoreductase]]


==References==
== References ==
{{reflist|1}}
{{InterPro content|IPR015409}}
{{Enzyme references|EC_number=1.1.1.27|IUBMB_EC_number=1/1/1/27}}
{{reflist|33em}}


==External links==
== Further reading ==
{{Enzyme links|EC_number=1.1.1.27|IUBMB_EC_number=1/1/1/27}}
{{refbegin|33em}}
* {{cite journal | vauthors = Johnson WT, Canfield WK | title = Intestinal absorption and excretion of zinc in streptozotocin-diabetic rats as affected by dietary zinc and protein. | journal = J Nutr | volume = 115 | issue = 9 | pages = 1217–27 | year = 1985 | pmid = 3897486 | doi =  }}
* {{cite journal | vauthors = Ein SH, Mancer K, Adeyemi SD | title = Malignant sacrococcygeal teratoma--endodermal sinus, yolk sac tumor--in infants and children: a 32-year review. | journal = J Pediatr Surg | volume = 20 | issue = 5 | pages = 473–7 | year = 1985 | pmid = 3903096 | doi = 10.1016/s0022-3468(85)80468-1 }}
* {{cite journal | vauthors = Azuma M, Shi M, Danenberg KD, Gardner H, Barrett C, Jacques CJ, Sherod A, Iqbal S, El-Khoueiry A, Yang D, Zhang W, Danenberg PV, Lenz HJ | title = Serum lactate dehydrogenase levels and glycolysis significantly correlate with tumor VEGFA and VEGFR expression in metastatic CRC patients. | journal = Pharmacogenomics | volume = 8 | issue = 12 | pages = 1705–13 | year = 2007 | pmid = 18086000 | doi = 10.2217/14622416.8.12.1705 }}
* {{cite journal | vauthors = Masepohl B, Klipp W, Pühler A | title = Genetic characterization and sequence analysis of the duplicated nifA/nifB gene region of Rhodobacter capsulatus. | journal = Mol Gen Genet | volume = 212 | issue = 1 | pages = 27–37 | year = 1988 | pmid = 2836706 | doi = 10.1007/bf00322441 }}
* {{cite journal | vauthors = Galardo MN, Regueira M, Riera MF, Pellizzari EH, Cigorraga SB, Meroni SB | title = Lactate Regulates Rat Male Germ Cell Function through Reactive Oxygen Species. | journal = PLoS ONE | volume = 9 | issue = 1 | pages = e88024 | year = 2014 | pmid = 24498241 | pmc = 3909278 | doi = 10.1371/journal.pone.0088024 }}
* {{cite journal | vauthors = Tesch P, Sjödin B, Thorstensson A, Karlsson J | title = Muscle fatigue and its relation to lactate accumulation and LDH activity in man. | journal = Acta Physiol Scand | volume = 103 | issue = 4 | pages = 413–20 | year = 1978 | pmid = 716962 | doi = 10.1111/j.1748-1716.1978.tb06235.x }}
* {{cite journal | vauthors = Beck O, Jernström B, Martinez M, Repke DB | title = In vitro study of the aromatic hydroxylation of 1-methyltetrahydro-beta-carboline (methtryptoline) in rat. | journal = Chem Biol Interact | volume = 65 | issue = 1 | pages = 97–106 | year = 1988 | pmid = 3345575 | doi = 10.1016/0009-2797(88)90034-8 }}
* {{cite journal | vauthors = Summermatter S, Santos G, Pérez-Schindler J, Handschin C | title = Skeletal muscle PGC-1α controls whole-body lactate homeostasis through estrogen-related receptor α-dependent activation of LDH B and repression of LDH A. | journal = Proc Natl Acad Sci U S A | volume = 110 | issue = 21 | pages = 8738–43 | year = 2013 | pmid = 23650363 | pmc = 3666691 | doi = 10.1073/pnas.1212976110 }}
* {{cite journal | vauthors = Robergs RA, Ghiasvand F, Parker D | title = Biochemistry of exercise-induced metabolic acidosis. | journal = Am J Physiol Regul Integr Comp Physiol | volume = 287 | issue = 3 | pages = R502-16 | year = 2004 | pmid = 15308499 | doi = 10.1152/ajpregu.00114.2004 }}
* {{cite journal | vauthors = Kresge N, Simoni RD, Hill RL | title = Otto Fritz Meyerhof and the elucidation of the glycolytic pathway. | journal = J Biol Chem | volume = 280 | issue = 4 | pages = e3 | year = 2005 | pmid = 15665335 | doi =  }}
{{refend}}


{{Alcohol oxidoreductases}}
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Revision as of 22:30, 8 September 2017

Lactate dehydrogenase
File:1i10.jpg
Lactate dehydrogenase M tetramer (LDH5), Human
Identifiers
EC number1.1.1.27
CAS number9001-60-9
Databases
IntEnzIntEnz view
BRENDABRENDA entry
ExPASyNiceZyme view
KEGGKEGG entry
MetaCycmetabolic pathway
PRIAMprofile
PDB structuresRCSB PDB PDBe PDBsum
Gene OntologyAmiGO / QuickGO

Lactate dehydrogenase (LDH or LD) is an enzyme found in nearly all living cells (animals, plants, and prokaryotes). LDH catalyzes the conversion of lactate to pyruvic acid and back, as it converts NAD+ to NADH and back. A dehydrogenase is an enzyme that transfers a hydride from one molecule to another.

LDH exist in four distinct enzyme classes. This article is specifically about the NAD(P)-dependent L-lactate dehydrogenase. Other LDHs act on D-lactate and/or are dependent on cytochrome c: D-lactate dehydrogenase (cytochrome)) and L-lactate (L-lactate dehydrogenase (cytochrome)).

LDH is expressed extensively in body tissues, such as blood cells and heart muscle. Because it is released during tissue damage, it is a marker of common injuries and disease such as heart failure.

Reaction

File:Reaction catalyzed by lactate dehydrogenase.png
Reaction catalyzed by lactate dehydrogenase
File:Lactate dehydrogenase mechanism.png
Arrow pushing mechanism for the reaction catalyzed by lactate dehydrogenase

Lactate dehydrogenase catalyzes the interconversion of pyruvate and lactate with concomitant interconversion of NADH and NAD+. It converts pyruvate, the final product of glycolysis, to lactate when oxygen is absent or in short supply, and it performs the reverse reaction during the Cori cycle in the liver. At high concentrations of lactate, the enzyme exhibits feedback inhibition, and the rate of conversion of pyruvate to lactate is decreased. It also catalyzes the dehydrogenation of 2-Hydroxybutyrate, but it is a much poorer substrate than lactate.

Active site

LDH in humans uses His(193) as the proton acceptor, and works in unison with the coenzyme (Arg99 and Asn138), and substrate (Arg106; Arg169; Thr248) binding residues.[1] The His(193) active site, is not only found in the human form of LDH, but is found in many different animals, showing the convergent evolution of LDH. The two different subunits of LDH: LDHA also known as the M subunit of LDH, and LDHB also known as the H subunit of LDH both retain the same active site, and the same amino acids participating in the reaction. The noticeable difference between the two subunits that make up LDH's tertiary structure is the replacement of alanine (in the M chain) with a glutamine (in the H chain). This tiny but notable change is believed to be the reason the H subunit can bind faster, and the M subunit's catalytic activity isn't reduced when subjected to the same conditions as the H subunit; while the H subunits activity is reduced fivefold.[2]

Isozymes

Lactate dehydrogenase is composed of four subunits (tetramer). The two most common subunits are the LDH-M and LDH-H protein, encoded by the LDHA and LDHB genes, respectively. These two subunits can form five possible tetramers (isoenzymes): 4H, 4M, and the three mixed tetramers (3H1M, 2H2M, 1H3M). These five isoforms are enzymatically similar but show different tissue distribution: The major isoenzymes of skeletal muscle and liver, M4, has four muscle (M) subunits, while H4 is the main isoenzymes for heart muscle in most species, containing four heart (H) subunits.

Usually LDH-2 is the predominant form in the serum. A LDH-1 level higher than the LDH-2 level (a "flipped pattern") suggests myocardial infarction (damage to heart tissues releases heart LDH, which is rich in LDH-1, into the bloodstream). The use of this phenomenon to diagnose infarction has been largely superseded by the use of Troponin I or T measurement.[citation needed]

There are two more mammalian LDH subunits that can be included in LDH tetramers: LDHC and LDHBx. LDHC is a testes-specific LDH protein, that is encoded by the LDHC gene. LDHBx is a peroxisome-specific LDH protein. LDHBx is the readthrough-form of LDHB. LDHBx is generated by translation of the LDHB mRNA, but the stop codon is interpreted as an amino acid-encoding codon. In consequence, translation continues to the next stop codon. This leads to the addition of seven amino acid acids to the normal LDH-H protein. The extension contains a peroxisomal targeting signal, so that LDHBx is imported into the peroxisome.[4]

Protein families

The family also contains L-lactate dehydrogenases that catalyse the conversion of L-lactate to pyruvate, the last step in anaerobic glycolysis. Malate dehydrogenases that catalyse the interconversion of malate to oxaloacetate and participate in the citric acid cycle, and L-2-hydroxyisocaproate dehydrogenases are also members of the family. The N-terminus is a Rossmann NAD-binding fold and the C-terminus is an unusual alpha+beta fold.[5][6]

Interactive pathway map

Click on genes, proteins and metabolites below to link to respective articles. [§ 1]

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Glycolysis and Gluconeogenesis edit
  1. ↑ The interactive pathway map can be edited at WikiPathways: "GlycolysisGluconeogenesis_WP534".

Enzyme regulation

This protein may use the morpheein model of allosteric regulation.[7]

Ethanol-induced hypoglycemia

Ethanol is dehydrogenated to acetaldehyde by alcohol dehydrogenase, and further into acetic acid by acetaldehyde dehydrogenase. During this reaction 2 NADH are produced. If large amounts of ethanol are present, then large amounts of NADH are produced, leading to a depletion of NAD+. Thus, the conversion of pyruvate to lactate is increased due to the associated regeneration of NAD+. Therefore, anion-gap metabolic acidosis (lactic acidosis) may ensue in ethanol poisoning.

The increased NADH/NAD+ ratio also can cause hypoglycemia in an (otherwise) fasting individual who has been drinking and is dependent on gluconeogenesis to maintain blood glucose levels. Alanine and lactate are major gluconeogenic precursors that enter gluconeogenesis as pyruvate. The high NADH/NAD+ ratio shifts the lactate dehydrogenase equilibrium to lactate, so that less pyruvate can be formed and, therefore, gluconeogenesis is impaired.

Substrate regulation

LDH is also regulated by the relative concentrations of its substrates. LDH becomes more active under periods of extreme muscular output due to an increase in substrates for the LDH reaction. When skeletal muscles are pushed to produce high levels of power, the demand for ATP in regards to aerobic ATP supply leads to an accumulation of free ADP, AMP, and Pi. The subsequent glycolytic flux, specifically production of NADH and pyruvate, exceeds the capacity for pyruvate dehydrogenase and other shuttle enzymes to metabolize pyruvate. The flux through LDH increases in response to increased levels of pyruvate and NADH to metabolize pyruvate into lactate.[8]

Transcriptional regulation

LDH undergoes transcriptional regulation by PGC-1α. PGC-1α regulates LDH by decreasing LDH A mRNA transcription and the enzymatic activity of pyruvate to lactate conversion.[9]

Genetics

The M and H subunits are encoded by two different genes:

Mutations of the M subunit have been linked to the rare disease exertional myoglobinuria (see OMIM article), and mutations of the H subunit have been described but do not appear to lead to disease.

Mutations

File:Mutated LDH-5.png
This is a mutant version of the LDH-5 enzyme, which is usually found in skeletal muscle

In rare cases, a mutation in the genes controlling the production of lactate dehydrogenase will lead to a medical condition known as lactate dehydrogenase deficiency. Depending on which gene carries the mutation, one of two types will occur: either lactate dehydrogenase-A deficiency (also known as glycogen storage disease XI) or lactate dehydrogenase-B deficiency. Both of these conditions affect how the body breaks down sugars, primarily in certain muscle cells. Lactate dehydrogenase-A deficiency is caused by a mutation to the LDHA gene, while lactate dehydrogenase-B deficiency is caused by a mutation to the LDHB gene.[10]

This condition is inherited in an autosomal recessive pattern, meaning that both parents must contribute a mutated gene in order for this condition to be expressed.[11]

A complete lactate dehydrogenase enzyme consists of four protein subunits.[12] Since the two most common subunits found in lactate dehydrogenase are encoded by the LDHA and LDHB genes, either variation of this disease causes abnormalities in many of the lactate dehydrogenase enzymes found in the body. In the case of lactate dehydrogenase-A deficiency, mutations to the LDHA gene results in the production of an abnormal lactate dehydrogenase-A subunit that cannot bind to the other subunits to form the complete enzyme. This lack of a functional subunit reduces the amount of enzyme formed, leading to an overall decrease in activity. During the anaerobic phase of glycolysis (the Cori Cycle), the mutated enzyme is unable to convert pyruvate into lactate to produce the extra energy the cells need. Since this subunit has the highest concentration in the LDH enzymes found in the skeletal muscles (which are the primary muscles responsible for movement), high-intensity physical activity will lead to an insufficient amount of energy being produced during this anaerobic phase.[13] This in turn will cause the muscle tissue to weaken and eventually break down, a condition known as rhabdomyolysis. The process of rhabdomyolysis also releases myoglobin into the blood, which will eventually end up in the urine and cause it to become red or brown: another condition known as myoglobinuria.[14] Some other common symptoms are exercise intolerance, which consists of fatigue, muscle pain, and cramps during exercise, and skin rashes.[15][16] In severe cases, myoglobinuria can damage the kidneys and lead to life-threatening kidney failure.[17] In order to obtain a definitive diagnosis, a muscle biopsy may be performed to confirm low or absent LDH activity. There is currently no specific treatment for this condition.

In the case of lactate dehydrogenase-B deficiency, mutations to the LDHB gene results in the production of an abnormal lactate dehydrogenase-B subunit that cannot bind to the other subunits to form the complete enzyme. As with lactate dehydrogenase-A deficiency, this mutation reduces the overall effectiveness in the enzyme.[18] However, there are some major differences between these two cases. The first is the location where the condition manifests itself. With lactate dehydrogenase-B deficiency, the highest concentration of B subunits can be found within cardiac muscle, or the heart. Within the heart, lactate dehydrogenase plays the role of converting lactate back into pyruvate so that the pyruvate can be used again to create more energy.[19] With the mutated enzyme, the overall rate of this conversion is decreased. However, unlike lactate dehydrogenase-A deficiency, this mutation does not appear to cause any symptoms or health problems linked to this condition.[16][20] At the present moment, it is unclear why this is the case. Affected individuals are usually discovered only when routine blood tests indicate low LDH levels present within the blood.

Role in muscular fatigue

The onset of acidosis during periods of intense exercise is commonly attributed to accumulation of lactic acid. From this reasoning, the idea of lactate production being a primary cause of muscle fatigue during exercise has been widely adopted. A closer, mechanistic analysis of lactate production under anaerobic conditions shows that there is no biochemical evidence for the production of lactate through LDH contributing to acidosis. While LDH activity is correlated to muscle fatigue,[21] the production of lactate by means of the LDH complex works as a system to delay the onset of muscle fatigue.

LDH works to prevent muscular failure and fatigue in multiple ways. The lactate-forming reaction generates cytosolic NAD+, which feeds into the glyceraldehyde 3-phosphate dehydrogenase reaction to help maintain cytosolic redox potential and promote substrate flux through the second phase of glycolysis to promote ATP generation. This, in effect, provides more energy to contracting muscles under heavy workloads. The production and removal of lactate from the cell also ejects a proton consumed in the LDH reaction- the removal of excess protons produced in the wake of this fermentation reaction serves to act as a buffer system for muscle acidosis. Once proton accumulation exceeds the rate of uptake in lactate production and removal through the LDH symport,[22] muscular acidosis occurs.

Medical relevance

LDH is a protein that normally appears throughout the body in small amounts. Many cancers can raise LDH levels, so LDH may be used as a tumor marker, but at the same time, it is not useful in identifying a specific kind of cancer. Measuring LDH levels can be helpful in monitoring treatment for cancer. Noncancerous conditions that can raise LDH levels include heart failure, hypothyroidism, anemia, pre-eclampsia, meningitis, encephalitis, acute pancreatitis, HIV and lung or liver disease.[23]

Tissue breakdown releases LDH, and therefore LDH can be measured as a surrogate for tissue breakdown, e.g. hemolysis. LDH is measured by the lactate dehydrogenase (LDH) test (also known as the LDH test or lactic acid dehydrogenase test). Comparison of the measured LDH values with the normal range help guide diagnosis.[24]

Cancer cells

File:LDH activity- normal vs canceous cells.png
Comparison of LDH activity in normal and cancerous cells

LDH is involved in tumor initiation and metabolism. Cancer cells rely on increased glycolysis resulting in increased lactate production in addition to aerobic respiration in the mitochondria, even under oxygen-sufficient conditions (a process known as the Warburg effect[25]). This state of fermentative glycolysis is catalyzed by the A form of LDH. This mechanism allows tumorous cells to convert the majority of their glucose stores into lactate regardless of oxygen availability, shifting use of glucose metabolites from simple energy production to the promotion of accelerated cell growth and replication. For this reason, LDH A and the possibility of inhibiting its activity has been identified as a promising target in cancer treatments focused on preventing carcinogenic cells from proliferating.

Chemical inhibition of LDH A has demonstrated marked changes in metabolic processes and overall survival carcinoma cells. Oxamate is a cytosolic inhibitor of LDH A that significantly decreases ATP production in tumorous cells as well as increasing production of reactive oxygen species (ROS). These ROS drive cancer cell proliferation by activating kinases that drive cell cycle progression growth factors at low concentrations,[26] but can damage DNA through oxidative stress at higher concentrations. Secondary lipid oxidation products can also inactivate LDH and impact its ability to regenerate NADH,[27] directly disrupting the enzymes ability to convert lactate to pyruvate.

While recent studies have shown that LDH activity is not necessarily an indicator of metastatic risk,[28] LDH expression can act as a general marker in the prognosis of cancers. Expression of LDH5 and VEGF in tumors and the stroma has been found to be a strong prognostic factor for diffuse or mixed-type gastric cancers.[29]

Hemolysis

In medicine, LDH is often used as a marker of tissue breakdown as LDH is abundant in red blood cells and can function as a marker for hemolysis. A blood sample that has been handled incorrectly can show false-positively high levels of LDH due to erythrocyte damage.

It can also be used as a marker of myocardial infarction. Following a myocardial infarction, levels of LDH peak at 3–4 days and remain elevated for up to 10 days. In this way, elevated levels of LDH (where the level of LDH1 is higher than that of LDH2, i.e. the LDH Flip, as normally, in serum, LDH2 is higher than LDH1) can be useful for determining whether a patient has had a myocardial infarction if they come to doctors several days after an episode of chest pain.

Tissue turnover

Other uses are assessment of tissue breakdown in general; this is possible when there are no other indicators of hemolysis. It is used to follow up cancer (especially lymphoma) patients, as cancer cells have a high rate of turnover, with destroyed cells leading to an elevated LDH activity.

Exudates and transudates

Measuring LDH in fluid aspirated from a pleural effusion (or pericardial effusion) can help in the distinction between exudates (actively secreted fluid, e.g. due to inflammation) or transudates (passively secreted fluid, due to a high hydrostatic pressure or a low oncotic pressure). The usual criterion (included in Light's criteria) is that a ratio of fluid LDH versus upper limit of normal serum LDH of more than 0.6[30] or ​2⁄3[31] indicates an exudate, while a ratio of less indicates a transudate. Different laboratories have different values for the upper limit of serum LDH, but examples include 200[32] and 300[32] IU/L.[33] In empyema, the LDH levels, in general, will exceed 1000 IU/L.

Meningitis and encephalitis

High levels of lactate dehydrogenase in cerebrospinal fluid are often associated with bacterial meningitis.[34] In the case of viral meningitis, high LDH, in general, indicates the presence of encephalitis and poor prognosis.

HIV

LDH is often measured in HIV patients as a non-specific marker for pneumonia due to Pneumocystis jirovecii (PCP). Elevated LDH in the setting of upper respiratory symptoms in an HIV patient suggests, but is not diagnostic for, PCP. However, in HIV-positive patients with respiratory symptoms, a very high LDH level (>600 IU/L) indicated histoplasmosis (9.33 more likely) in a study of 120 PCP and 30 histoplasmosis patients.[35]

Dysgerminoma

Elevated LDH can be an early clinical sign of a rare malignant cell tumor called a dysgerminoma. Not all dysgerminomas produce LDH, and this is often a non-specific finding.

Prokaryotes

A cap-membrane-binding domain is found in prokaryotic lactate dehydrogenase. This consists of a large seven-stranded antiparallel beta-sheet flanked on both sides by alpha-helices. It allows for membrane association.[36]

See also

References

This article incorporates text from the public domain Pfam and InterPro: IPR015409
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  2. ↑ Eventoff W, Rossmann MG, Taylor SS, Torff HJ, Meyer H, Keil W, Kiltz HH (Jul 1977). "Structural adaptations of lactate dehydrogenase isozymes" (PDF). Proceedings of the National Academy of Sciences of the United States of America. 74 (7): 2677–81. doi:10.1073/pnas.74.7.2677. PMC 431242. PMID 197516.
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  6. ↑ Madern D (2002). "Molecular evolution within the L-malate and L-lactate dehydrogenase super-family". J Mol Evol. 54 (6): 825–40. doi:10.1007/s00239-001-0088-8. PMID 12029364.
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  16. ↑ 16.0 16.1 "Glycogenoses". neuromuscular.wustl.edu. Retrieved 2016-03-02.
  17. ↑ "Glycogen storage disease XI - Conditions - GTR - NCBI". www.ncbi.nlm.nih.gov. Retrieved 2016-03-02.
  18. ↑ "LDHB gene". Genetics Home Reference. 2016-02-29. Retrieved 2016-03-02.
  19. ↑ "Lactate Dehydrogenase - Worthington Enzyme Manual". www.worthington-biochem.com. Retrieved 2016-03-02.
  20. ↑ "OMIM Entry # 614128 - LACTATE DEHYDROGENASE B DEFICIENCY; LDHBD". www.omim.org. Retrieved 2016-03-02.
  21. ↑ Tesch P, Sjödin B, Thorstensson A, Karlsson J (1978). "Muscle fatigue and its relation to lactate accumulation and LDH activity in man". Acta Physiol Scand. 103 (4): 413–20. doi:10.1111/j.1748-1716.1978.tb06235.x. PMID 716962.
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  23. ↑ Stanford Cancer Center. "Cancer Diagnosis - Understanding Cancer". Understanding Cancer. Stanford Medicine.
  24. ↑ "Lactate dehydrogenase test: MedlinePlus Medical Encyclopedia". MedlinePlus. U.S. National Library of Medicine.
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  27. ↑ Ramanathan R, Mancini RA, Suman SP, Beach CM (2014). "Covalent Binding of 4-Hydroxy-2-nonenal to Lactate Dehydrogenase Decreases NADH Formation and Metmyoglobin Reducing Activity". J Agric Food Chem. 62 (9): 2112–7. doi:10.1021/jf404900y. PMID 24552270.
  28. ↑ Xu HN, Kadlececk S, Profka H, Glickson JD, Rizi R, Li LZ (2014). "Is Higher Lactate an Indicator of Tumor Metastatic Risk? A Pilot MRS Study Using Hyperpolarized (13)C-Pyruvate". Acad Radiol. 21 (2): 223–31. doi:10.1016/j.acra.2013.11.014. PMID 24439336.
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  34. ↑ Stein JH (1998). Internal Medicine. Elsevier Health Sciences. pp. 1408–. ISBN 978-0-8151-8698-4. Retrieved 12 August 2013.
  35. ↑ Butt AA, Michaels S, Greer D, Clark R, Kissinger P, Martin DH (July 2002). "Serum LDH level as a clue to the diagnosis of histoplasmosis". AIDS Read. 12 (7): 317–21. PMID 12161854.
  36. ↑ Dym O, Pratt EA, Ho C, Eisenberg D (August 2000). "The crystal structure of D-lactate dehydrogenase, a peripheral membrane respiratory enzyme". Proc. Natl. Acad. Sci. U.S.A. 97 (17): 9413–8. doi:10.1073/pnas.97.17.9413. PMC 16878. PMID 10944213.

Further reading

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