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a complex biopolymer consisting of protein and carbohydrate components bonded covalently. Mucoproteins are widely distributed in nature. They are components of such secretions in animals and man as saliva, gastric juice, and cerebrospinal fluid, as well as of blood plasma, erythrocytes, urine, chicken egg albumin, the eggs of amphibians and invertebrates, and the cell wall of microorganisms. A number of enzymes and hormones are classified as mucoproteins.
Mucoproteins differ in protein content and in the structure and size of the carbohydrate fraction. They usually contain up to 85 percent protein. Blood elements, however, are the exception, containing up to 80 percent carbohydrates. The carbohydrate fraction of mucoproteins includes the following monosaccharides: N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, D-mannose, fucose, N-acetyl(glycolyl)neuraminic acid, and D-galactose. The peptide chains contain the common amino acids. The biosynthesis of the peptide chains takes place in the ribosomes, while the synthesis of the carbohydrate chains occurs in the Golgi complex with the help of specific enzymes —glycosyltransferases.
The biological functions of mucoproteins are highly varied. They determine the immune properties of the body, the blood-group affiliation, and the elasticity and permeability of tissues. They also participate in intercellular interactions. These functions are primarily determined by the structure of the carbohydrate chains of the mucoproteins. The term “glycoprotein” is more frequently used than “mucoprotein.”
REFERENCESDerevitskaia, V. A. “Khimiia glikoproteinov.” Uspekhi biologicheskoi khimii, 1967, vol. 8.
Khimiia uglevodov. Moscow, 1967.
Glikoproteiny, vols. 1–2. Moscow, 1969. (Translated from English.)
N. D. GABRIELIAN