Mannose enters the carbohydrate metabolism stream in two steps:
- First it undergoes phosphorylation to mannose-6-phosphate by hexokinase.
- Then, it is converted to fructose-6-phosphate by mannose phosphate isomerase.
Mannose can be formed by the oxidation of mannitol.
It can also be formed from D-glucose in the Lobry-de Bruyn-van Ekenstein transformation
The root of both "mannose" and "manitol" is manna, which the Bible records as the food supplied to the Israelites during their journey through the Sinai Peninsula. Manna is a sweet secretion of several trees and shrubs, such as Fraxinus ornus.
The fact that D-mannose has the same configuration at its penultimate carbon as D-glyceraldehyde is unsurprising as that is what defines the dextro classification. However, mannose differs from D-glucose by inversion of the C2 chiral centre. This apparently simple change leads to the drastically different chemistry of the two hexoses, as it does the remaining six hexoses.
The hexoses can be remembered conveniently by the following phrase:
- "All (allose) altruists (altrose) gladly (glucose) make (mannose) gum (gulose) in (idose) gallon (galactose) tanks (talose)."