mucopolysaccharide

mucopolysaccharide

(myo͞o'kəpŏlēsăk`ərīd), class of polysaccharide molecules, also known as glycosaminoglycans, composed of amino-sugars chemically linked into repeating units that give a linear unbranched polymeric compound. The monomeric amino-sugar constituents are ordinary monosaccharides that contain a nitrogen atom covalently bound to one of the ring carbons of the sugar portion. The nitrogen is, in turn, either bonded to two atoms of hydrogen (termed a primary amino-group) or to another carbon atom (hence, a substituted amino-group). The mucopolysaccharides are quite similar structurally to the more well-known animal and plant polysaccharides such as glycogen and starch. Chitin is a particularly plentiful mucopolysaccharide and serves, like cellulose does in plants, as a structural polysaccharide for many phyla of lower plants and animals. The shells of lobsters, crayfish, crabs, insects, and many other invertebrate organisms contain mostly chitin complexed with inorganic salts. The copepods, a group of microscopic marine organisms of the subphylum Crustacea, alone are considered to synthesize about 10⁹ tons of chitin per year. Chitin is probably the second most abundant large organic compound on earth (the first being cellulose). Heparin, an anticoagulant used widely in the treatment of blood clotting disorders, such as pulmonary embolus, is a mucopolysaccharide. Another important compound of this class is hyaluronic acid, a molecule found universally in the connective tissues of animals and in the fluids of their eyes and joints. Hyaluronic acid in association with protein has been isolated from various organisms, and such complexes are thought to bind water in the cellular spaces, thus holding cells together in a jellylike matrix. In addition, such substances may provide the fluids of joints with lubricating and shock-absorbing qualities. Many other mucopolysaccharides are, like hyaluronic acid, associated with proteins; the separation between such proteoglycans and glycoproteins is somewhat arbitrary, but the latter compounds are distinguished by their relative paucity of sugars.

Mucopolysaccharide

 

a carbohydrate-protein polymer containing 70 to 80 percent carbohydrates. Most extensively studied have been the various types of acid mucopolysaccharides in connective tissue, in the synovia of the joints, and in the vitreous body of the eye.

The major types of mucopolysaccharides are hyaluronic acid, heparin, chondroitin sulfuric acids, and keratosulfate (found in cartilage and cornea). The carbohydrate portion of acid mucopolysaccharides is a linear polysaccharide consisting of periodically repeating units with N-sulfoaminosugar or N-acetylaminosugar residues (D-glucosamine or D-galactosamine) and uronic acid. The sulfuric acid residues in sulfate mucopolysaccharides are bound to the hydroxyl groups of monosaccharide components. Acid mucopolysaccharides differ widely in molecular weight, in binding energy of the components, and in functional properties.

Owing to their capacity to bind and hold water, acid mucopolysaccharides serve as a natural lubricant in the joints and impart elasticity to connective tissue. As a component of cartilage and ligaments, mucopolysaccharides are involved in support and motor functions. They also have bactericidal properties.

With aging, the composition of the mucopolysaccharides in connective tissue changes. Dysfunction in the mucopolysaccharide metabolism leads to a change in the composition of connective tissue and of the body fluids, resulting in diseases such as collagenosis, mucopolysaccharidosis, and rheumatism.

REFERENCES

Stacey, M., and S. Barker. Uglevody zhivykh tkanei. Moscow, 1965. (Translated from English.)
Stepanenko, B. N. Uglevody: Uspekhi v izuchenii stroeniia i metabolizma. Moscow, 1968.
Kasavina, B. S., T. A. Kol’chinskii, and G. D. Zenkevich. “Mukopolisakharidy kostnoi i khriashchevoi tkani v norme i patologii.” Uspekhi sovremennoi biologii, 1970, vol. 69, issue 3.

N. D. GABRIELIAN

mucopolysaccharide

[¦myü·kō‚päl·ē′sak·ə‚rīd]

(biochemistry)

Any of a group of polysaccharides containing an amino sugar and uronic acid; a constituent of mucoproteins, glycoproteins, and blood-group substances.