Mannans are

polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

s containing the sugar

mannose Mannose is a sugar monomer of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylation of certain proteins. Several congenital disorders of glycosylat ...

as a principal component. They are a type of

polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with w ...

comprise hemicellulose, a major source of biomass found in higher plants such as softwoods. These polymers also typically contain two other sugars,

galactose Galactose (, '' galacto-'' + ''-ose'', "milk sugar"), sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweet as glucose, and about 65% as sweet as sucrose. It is an aldohexose and a C-4 epimer of glucose. A galactose molecu ...

and

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...

. They are often branched (unlike cellulose).

Structural diversity

Plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...

mannans have β(1-4) linkages, occasionally with α(1-6)

branches, forming galactomannans. They are insoluble and a form of storage polysaccharide. Ivory nut is a source of mannans. An additional type is galactoglucomannan found in soft wood with a mixed mannose/glucose β(1-4) backbone. Many mannans are acetylated and some from marine sources, have sulfate esters side chains.

Yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...

and some plants such as

conjac Konjac (or konjak, ) is a common name of the East and Southeast Asian plant ''Amorphophallus konjac'' (syn. ''A. rivieri''), which has an edible corm (bulbo-tuber). It is also known as konjaku, konnyaku potato, devil's tongue, voodoo lily, s ...

and

salep Salep, also spelled sahlep or sahlab,( tr, salep, sahlep; fa, ثعلب, ; ar, سحلب, ; al, salep; az, səhləb; he, סַחְלָבּ, ; el, σαλέπι, ; Serbian, Macedonian, Bulgarian and Bosnian: салеп, ''salep'') is a flour ma ...

have a different type of mannans in their cell wall, with a α(1-6) linked backbone and α(1-2) and α(1-3) linked

branches, hence " glucomannan". It is water soluble. It is serologically similar to structures found on mammalian glycoproteins. Detection of mannan leads to lysis in the mannan-binding lectin pathway.

Synthesis and degradation

GDP-mannose is a substrate for

glycosyltransferase Glycosyltransferases (GTFs, Gtfs) are enzymes (EC 2.4) that establish natural glycosidic linkages. They catalyze the transfer of saccharide moieties from an activated nucleotide sugar (also known as the "glycosyl donor") to a nucleophilic glyco ...

for enzymes called mannosyltransferases.

Biosynthesis

GDP-mannose is produced from GTP and

mannose-6-phosphate Mannose-6-phosphate (M6P) is a molecule bound by lectin in the immune system. M6P is converted to fructose 6-phosphate by mannose phosphate isomerase. M6P is a key targeting signal for acid hydrolase precursor proteins that are destined for tran ...

by the enzyme mannose-1-phosphate guanylyltransferase. The degradation of mannans (and many related forms of hemicellulose) has been well studied. The hydrolysis of the main mannan backbone is catalyzed by various enzymes including β- mannosidase, β- glucosidase, and β-

mannase Beta-mannosidase (, ''mannanase'', ''mannase'', ''beta-D-mannosidase'', ''beta-mannoside mannohydrolase'', ''exo-beta-D-mannanase'', ''lysosomal beta A mannosidase'') is an enzyme with systematic name ''beta-D-mannoside mannohydrolase'', which ...

. The side chains are degraded by

esterase An esterase is a hydrolase enzyme that splits esters into an acid and an alcohol in a chemical reaction with water called hydrolysis. A wide range of different esterases exist that differ in their substrate specificity, their protein structure ...

s and α-galactosidase. When a long chain of mannan is

hydrolyzed Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis ...

into shorter chains, these smaller molecules are known as mannan

oligosaccharide An oligosaccharide (/ˌɑlɪgoʊˈsækəˌɹaɪd/; from the Greek ὀλίγος ''olígos'', "a few", and σάκχαρ ''sácchar'', "sugar") is a saccharide polymer containing a small number (typically two to ten) of monosaccharides (simple sug ...

(MOS). MOS by definition can be produced from either insoluble galactomannan or soluble glucomannan, although the latter type is more widely marketed. Glucomannan MOS is used as prebiotics in animal husbandry and nutritional supplements due to its bioactivity.

Etymology

From ' manna', produced by several species of tree and shrub e.g. ''

Fraxinus ornus ''Fraxinus'' (), commonly called ash, is a genus of flowering plants in the olive and lilac family, Oleaceae. It contains 45–65 species of usually medium to large trees, mostly deciduous, though a number of subtropical species are evergr ...

'' from whose secretions

mannitol Mannitol is a type of sugar alcohol used as a sweetener and medication. It is used as a low calorie sweetener as it is poorly absorbed by the intestines. As a medication, it is used to decrease pressure in the eyes, as in glaucoma, and to lo ...

was originally isolated.

References

Carbohydrates Polysaccharides {{chemistry-stub

Structural diversity

Synthesis and degradation

Biosynthesis

Etymology

Further reading

See also

References