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Biochemistry
March 20, 2025 | UR Gate

Mannose: Structure, Properties, Biological Importance, and Metabolism



1. Introduction

Mannose is a monosaccharide that belongs to the hexose sugar family. It is an important component of glycoproteins and plays a crucial role in various biological functions, including cell signaling, immune response, and metabolism. Mannose is naturally found in fruits, vegetables, and certain microorganisms.


2. Chemical Structure and Physical Properties

Mannose has the molecular formula C6H12O6 and is an epimer of glucose, differing in the orientation of the hydroxyl group at the C-2 position.

Properties:

  • Solubility: Highly soluble in water.
  • Taste: Slightly sweet.
  • Reactivity: Participates in glycosylation, metabolism, and energy production.

3. Mannose Metabolism

Mannose metabolism is essential for the biosynthesis of glycoproteins and glycolipids. It is efficiently absorbed in the intestine and utilized in various biochemical pathways.

3.1 Absorption and Phosphorylation

  • After ingestion, mannose is absorbed in the small intestine and transported to the liver via the portal vein.
  • In hepatocytes, mannose is phosphorylated by hexokinase to form mannose-6-phosphate (M6P).

3.2 Conversion into Fructose-6-Phosphate

  • Mannose-6-phosphate is isomerized into fructose-6-phosphate (F6P) by the enzyme phosphomannose isomerase.
  • Fructose-6-phosphate enters the glycolysis pathway, where it is converted into pyruvate for energy production.

3.3 Role in Glycosylation

  • Mannose is an essential precursor in the N-linked glycosylation of proteins, which is crucial for proper protein folding and function.
  • It is incorporated into glycoproteins in the endoplasmic reticulum (ER) and Golgi apparatus.



4. Effects of Mannose on Health

4.1 Benefits

  • Supports immune function by preventing bacterial adhesion to the urinary tract (used in UTI treatment).
  • Essential for glycoprotein synthesis, which is vital for cellular communication.
  • Provides an alternative energy source through its conversion into fructose-6-phosphate.

4.2 Risks

  • Mannose metabolism disorders, such as congenital disorders of glycosylation (CDG), can lead to developmental and metabolic complications.
  • Excessive intake may cause digestive discomfort or alter blood sugar levels.

5. Conclusion

Mannose is a vital monosaccharide involved in energy metabolism, glycoprotein synthesis, and immune defense. Its metabolism is interconnected with glycolysis and glycosylation pathways, making it essential for various physiological processes. Understanding mannose metabolism contributes to advancements in medical research and therapeutic applications.


1- National Center for Biotechnology Information. (2022). PubChem Compound Summary for CID 18950, D-Mannose. Retrieved from 
2- Alton, G., Hasilik, M., Niehues, R., Panneerselvam, K., Etchison, D., Fana, F., ... & Freeze, H. H. (1997). Direct utilization of mannose for mammalian glycoprotein biosynthesis. Glycobiology, 7(3), 285-295.
3- Freeze, H. H. (2002). Human disorders in N-glycosylation and animal models. Biochimica et Biophysica Acta (BBA) - General Subjects, 1573(3), 388-393.
4- Klein, A. (2002). Glycoprotein Mannosylation: Structural Aspects and Functional Implications. Acta Biochimica Polonica, 49(2), 323-330.
5- Panin, V. M., Wells, L., Panin, A., & Lennarz, W. J. (2002). Metabolic pathways for N-linked glycosylation and processing of glycoproteins. Biochimica et Biophysica Acta (BBA) - General Subjects, 1573(3), 325-336.

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