Die Grundstruktur der Glykoproteine und ihr enzymatischer Abbau

Abstract

Covalent carbohydrate-protein compounds are widely distributed in animals, both in vertebrates and invertebrates. Recently their occurrence in plants has been shown. The fundamental structure of all members of this group is the same. They have as a core a polypeptide chain or chains; to the functional groups of the side-chains of constituent amino acids are linked covalently carbohydrate chains. According to the composition and structure of the carbohydrate chain two classes of carbohydrate-protein compounds may be distinguished: Firstly, proteoglycans; their carbohydrate moiety consists of small repeating units, usually a disaccharide residue, arranged in a linear structure of mol.wt. about 20,000 to 35,000. Secondly, glycoproteins; their carbohydrate moiety contains in most cases an amino sugar (glucosamine and/or galactosamine) and one or more of the following monosaccharides: D-galactose, D-mannose, L-fucose, D-glucose, sialic acid. The carbohydrate chain is nearly always branched, of low mol. weight and so far the presence of a repeating unit has not been reported.
One of the simplest, and for this reason best understood, glycoproteins is ovine submaxillary mucoprotein (OSM). The chemistry and structure of its carbohydrate moiety, the type of linkage between carbohydrate and the polypeptide chain, its physico-chemical properties and the enzymes involved in its degradation are described.