Metabolism
| Metabolism of common monosaccharides and some biochemical reactions of glucose |
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While much of the mannose used in glycosylation is believed to be derived from glucose, in cultured hepatoma (liver-derived) cells, most of the mannose for glycoprotein biosynthesis comes from extracellular mannose, not glucose. Many of the glycoproteins produced in the liver are secreted into the bloodstream, so dietary mannose is distributed throughout the body.
Mannose is present in numerous glycoconjugates including N-linked glycosylation of proteins. C-mannosylation is also abundant and can be found in collagen-like regions.
The digestion of many polysaccharides and glycoproteins yields mannose which is phosphorylated by hexokinase to generate mannose-6-phosphate. Mannose-6-phosphate is converted to fructose-6-phosphate, by the enzyme phosphomannose isomerase, and then enters the glycolytic pathway or is converted to glucose-6-phosphate by the gluconeogenic pathway of hepatocytes.
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