 D-Mannopyranose | |
 Fischer projections | |
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| Names | |
|---|---|
| IUPAC names Mannose manno-Hexose[1] | |
| Systematic IUPAC name (3S,4S,5S,6R)-6-(hydroxymethyl)oxane-2,3,4,5-tetrol | |
| Identifiers | |
| ChEMBL | |
| ChemSpider |
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| KEGG | |
| MeSH | Mannose |
| UNII | |
| Properties | |
| C6H12O6 | |
| Molar mass | 180.156 g·mol−1 |
| Appearance | white solid |
| Density | 1.554 g/cm3 |
| Melting point | 132 °C (270 °F; 405 K) |
| -102.90·10−6 cm3/mol | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Mannose is asugar with the formulaHOCH2(CHOH)4CHO, which sometimes is abbreviatedMan. It is one of themonomers of thealdohexose series ofcarbohydrates. It is a C-2epimer ofglucose. Mannose is important in humanmetabolism, especially in theglycosylation of certainproteins. Severalcongenital disorders of glycosylation are associated with mutations inenzymes involved in mannose metabolism.[2]
Mannose is not anessential nutrient; it can be produced in the human body from glucose, or converted into glucose. Mannose provides 2–5 kcal/g. It is partially excreted in theurine.
The root of both "mannose" and "mannitol" ismanna, which theBible describes as the food supplied to the Israelites during their journey in the region ofSinai. Several trees and shrubs can produce a substance called manna, such as the "manna tree" (Fraxinus ornus) from whose secretions mannitol was originally isolated.[citation needed]
Mannose commonly exists as two different-sized rings, thepyranose (six-membered) form and thefuranose (five-membered) form. Each ring closure can have either an alpha or beta configuration at theanomeric position. The chemical rapidly undergoesisomerization among these four forms.[citation needed]
 α-D-Mannofuranose 0.6% |  β-D-Mannofuranose 0.2% |
 α-D-Mannopyranose 63.7% |  β-D-Mannopyranose 35.5% |
While much of the mannose used in glycosylation is believed to be derived from glucose, inculturedhepatoma cells (cancerous cells from the liver), most of the mannose for glycoprotein biosynthesis comes from extracellular mannose, not glucose.[4] Many of the glycoproteins produced in the liver are secreted into the bloodstream, so dietary mannose is distributed throughout the body.[5]
Mannose is present in numerous glycoconjugates includingN-linked glycosylation of proteins.C-Mannosylation is also abundant and can be found in collagen-like regions.[citation needed]
The digestion of manypolysaccharides and glycoproteins yields mannose, which is phosphorylated byhexokinase to generatemannose-6-phosphate. Mannose-6-phosphate is converted tofructose-6-phosphate, by the enzymephosphomannose isomerase, and then enters theglycolytic pathway or is converted toglucose-6-phosphate by thegluconeogenic pathway ofhepatocytes.[citation needed]
Mannose is a dominant monosaccharide inN-linked glycosylation, which is apost-translational modification of proteins. It is initiated by theen bloc transfer on Glc3Man9GlcNAc2 to nascent glycoproteins in theendoplasmic reticulum (ER) in a co-translational manner as the protein entered through the transport system. Glucose ishydrolyzed on fully folded protein and the mannose moieties are hydrolyzed by ER andGolgi-residentmannosidases. Typically, mature human glycoproteins only contain three mannose residues buried under sequential modification by GlcNAc,galactose, andsialic acid. This is important, as theinnate immune system in mammals is geared to recognise exposed mannose residues. This activity is due to the prevalence of mannose residues, in the form of mannans, on the surfaces of yeasts. Thehuman immunodeficiency virus displays considerable amount of mannose residues due to the tight clustering of glycans in itsviral spike.[6][7] These mannose residues are the target forbroadly neutralizing antibodies.[8]
Recombinant proteins produced in yeast may be subject to mannose addition in patterns different from those used by mammalian cells.[9] This difference in recombinant proteins from those normally produced in mammalian organisms may influence the effectiveness of vaccines.[citation needed]
Mannose can be formed by the oxidation ofmannitol.[citation needed]
It can also be formed from glucose in theLobry de Bruyn–van Ekenstein transformation.[citation needed]
Mannose (D-mannose) is used as adietary supplement to prevent recurrenturinary tract infections (UTIs).[10][11] As of 2022[update], one review found that taking mannose was as effective asantibiotics to prevent UTIs,[10] while another review found thatclinical trial quality was too low to allow any conclusion about usingD‐mannose to prevent or treat UTIs.[11] In 2024, a randomized clinical trial among 598 women with recurrent UTI recruited from primary care settings found the proportion experiencing a medically attended UTI was 51.0% in those taking dailyD-mannose over 6 months and 55.7% in those taking placebo, concluding thatD-mannose should not be recommended to prevent future episodes of medically attended UTI in women with recurrent UTI in primary care.[12][13]
Mannose differs from glucose by inversion of the C-2chiral center. Mannose displays a pucker in the solution ring form. This simple change leads to the drastically different biochemistry of the twohexoses. This change has the same effect on the otheraldohexoses, as well.[citation needed]
The PEP-dependent sugar transporting phosphotransferase system transports and simultaneously phosphorylates its sugar substrates. Mannose XYZ permease is a member of the family, with this distinct method being used by bacteria for sugar uptake particularly exogenous hexoses in the case of mannose XYZ to release the phosphate esters into the cell cytoplasm in preparation for metabolism primarily through the route of glycolysis.[14] The MANXYZ transporter complex is also involved in infection ofE. coli bybacteriophage lambda, with subunit ManY and ManZ being sufficient for proper lambda phage infection.[15]MANXYZ possesses four domains in three polypeptide chains; ManX, ManY, and ManZ. The ManX subunit forms ahomodimer that is localized to the cytoplasmic side of the membrane. ManX contains two domains IIA and IIB linked by a hinge peptide with each domain containing a phosphorylation site and phosphoryl transfer occurs between both subunits.[16] ManX can be membrane bound or not.[15] The ManY and ManNZ subunits are hydrophobic integral membrane proteins with six and one transmembrane alpha helical spanner(s).[17][18][19] The phosphoryl group of PEP is transferred to the imported sugar via Enzyme 1, histidine protein phosphate carrier, and then to the ManX, ManY, and ManZ subunits of the ManXYZ transportation complex, which phosphorylates the entering hexose sugar, creating a hexose-6-phosphate.[citation needed]
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