Mannans are

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

s containing the sugar

mannose Mannose is a sugar with the formula , which sometimes is abbreviated Man. It is one of the monomers of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylatio ...

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 wat ...

found in

hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant cell walls. Cellulose is crystalline, strong, an ...

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

galactose Galactose (, ''wikt:galacto-, galacto-'' + ''wikt:-ose#Suffix 2, -ose'', ), sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweetness, sweet as glucose, and about 65% as sweet as sucrose. It is an aldohexose and a C-4 epime ...

and

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

. They are often branched (unlike cellulose).

Structural diversity

Plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

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 ester In organosulfur chemistry, organosulfates are a class of organic compounds sharing a common functional group with the structure . The core is a sulfate group and the R group is any Organyl group, organic residue. All organosulfates are formally ...

s side chains.

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

and some plants such as conjac and

salep Salep, also spelled sahlep salepi or sahlab,; ; ; ; ; ; ; ; ; ; is a flour made from the tubers of the orchid genus ''Orchis'' (including species '' Orchis mascula'' and ''Orchis militaris''). These tubers contain a nutritious, starchy polysacc ...

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 Glucomannan is a water-soluble polysaccharide that is considered a dietary fiber. It is a hemicellulose component in the Cell wall#Plant cell walls, cell walls of some plant species. Glucomannan is a food additive used as an emulsifier and thick ...

". 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 gl ...

for enzymes called mannosyltransferases.

Biosynthesis

GDP-mannose is produced from GTP and mannose-6-phosphate 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 Glucosidases are the glycoside hydrolase enzymes categorized under the EC number 3.2.1. Function Alpha-glucosidases are enzymes involved in breaking down complex carbohydrates such as starch and glycogen into their monomers. They catalyze the ...

, and β- mannase. The side chains are degraded by

esterase In biochemistry, an esterase is a class of enzyme that splits esters into an acid and an alcohol in a chemical reaction with water called hydrolysis (and as such, it is a type of hydrolase). A wide range of different esterases exist that differ ...

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 hydrolysi ...

into shorter chains, these smaller molecules are known as mannan

oligosaccharide An oligosaccharide (; ) is a carbohydrate, saccharide polymer containing a small number (typically three to ten) of monosaccharides (simple sugars). Oligosaccharides can have many functions including Cell–cell recognition, cell recognition and ce ...

(MOS). MOS by definition can be produced from either insoluble galactomannan or soluble glucomannan, although the latter type is more widely marketed.

Glucomannan Glucomannan is a water-soluble polysaccharide that is considered a dietary fiber. It is a hemicellulose component in the Cell wall#Plant cell walls, cell walls of some plant species. Glucomannan is a food additive used as an emulsifier and thick ...

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 ornus'', the manna ash or South European flowering ash, is a species of ''Fraxinus'' native to Southern Europe and Southwestern Asia, from Spain and Italy north to Austria and the Czech Republic, and east through the Balkans, Turkey, a ...

'' 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 l ...

was originally isolated.

Structural diversity

Synthesis and degradation

Biosynthesis

Etymology

See also

References

Further reading