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 glycosylation ...

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 wa ...

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 molec ...

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, using ...

. 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 exclud ...

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

branches, forming

galactomannan Galactomannans are polysaccharides consisting of a mannose backbone with galactose side groups, more specifically, a (1-4)-linked beta-D-mannopyranose backbone with branchpoints from their 6-positions linked to alpha-D-galactose, (i.e. 1-6-linke ...

s. They are insoluble and a form of storage polysaccharide. Ivory nut is a source of mannans. An additional type is

galactoglucomannan Galactoglucomannan is a water-soluble hemicellulose, consisting of galactose, glucose and mannose. Many softwood species, e.g. Norway spruce are rich of galactoglucomannans and can contain it up to 10–20%. Structure Galactoglucomannan consists ...

found in soft wood with a mixed mannose/glucose β(1-4) backbone. Many mannans are

acetylated : In organic chemistry, acetylation is an organic esterification reaction with acetic acid. It introduces an acetyl group into a chemical compound. Such compounds are termed ''acetate esters'' or simply ''acetates''. Deacetylation is the opposit ...

and some from marine sources, have

sulfate ester Organosulfates are a class of organic compounds sharing a common functional group with the structure R-O-SO3−. The SO4 core is a sulfate group and the R group is any organic residue. All organosulfates are formally esters derived from alcohols ...

s 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 constitut ...

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, sn ...

and

salep Salep, also spelled sahlep or sahlab,( tr, salep, sahlep; fa, ثعلب, ; ar, سحلب, ; al, salep; az, səhləb; he, סַחְלָבּ, ; el, σαλέπι, ; Serbian language, Serbian, Macedonian language, Macedonian, Bulgarian language, Bu ...

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 walls of some plant species. Glucomannan is a food additive used as an emulsifier and thickener. It is a major source ...

". 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 The lectin pathway or lectin complement pathway is a type of cascade reaction in the complement system, similar in structure to the classical complement pathway, in that, after activation, it proceeds through the action of C4 and C2 to produce acti ...

Synthesis and degradation

GDP-mannose Guanosine diphosphate mannose or GDP-mannose is a nucleotide sugar that is a substrate for glycosyltransferase reactions in metabolism. This compound is a substrate for enzymes called mannosyltransferases. Known as donor of activated mannose in al ...

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 glycos ...

for enzymes called

mannosyltransferase A mannosyltransferase is a type of glycosyltransferase that acts upon 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 glyco ...

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 transp ...

by the enzyme

mannose-1-phosphate guanylyltransferase In enzymology, a mannose-1-phosphate guanylyltransferase () is an enzyme that catalyzes the chemical reaction :GTP + alpha-D-mannose 1-phosphate \rightleftharpoons diphosphate + GDP-mannose Thus, the two substrates of this enzyme are GTP and ...

. 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 Mannosidase is an enzyme which hydrolyses mannose. There are two types: * alpha-Mannosidase * beta-Mannosidase A deficiency is associated with mannosidosis Mannosidosis is a deficiency in mannosidase, an enzyme. There are two types: * Alpha-manno ...

, 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 t ...

, 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 sugar ...

(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 walls of some plant species. Glucomannan is a food additive used as an emulsifier and thickener. It is a major source ...

MOS is used as prebiotics in animal husbandry and nutritional supplements due to its bioactivity.

Etymology

From '

manna Manna ( he, מָן, mān, ; ar, اَلْمَنُّ; sometimes or archaically spelled mana) is, according to the Bible, an edible substance which God provided for the Israelites during their travels in the desert during the 40-year period follow ...

', 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 lower ...

was originally isolated.

References

Carbohydrates Polysaccharides {{chemistry-stub

Structural diversity

Synthesis and degradation

Biosynthesis

Etymology

Further reading

See also

References