The Resistance of Glycoproteins to Proteolytic Inactivation.

Abstract

The carbohydrate constituents of globular glycoproteins are probably located at the surface and may thus be expected to act as local shields and enhance the protection of the polypeptide towards degradation by proteolytic enzymes. Previous studies using carbohydrates covalently bound to polypeptides indicated that a considerable increase in stability towards inactivation by heat and by proteolytic enzymes may be imparted to proteins in this way. In the present study, the proteolysis of different fractions of a lysozyme-dextran T10 preparation as well as the inactivation by autolysis of chymotrypsin, trypsin and their dextran conjugates, was examined. The lysozyme fraction with the highest content of carbohydrate was most resistant to inactivation by chymotrypsin. Assays of the proteolytic activity in the different incubation mixtures with lysozyme and its conjugates indicate that the results can not be due to variations in the activity of chymotrypsin. The protective influence of carbohydrate constituents attached by the CNBr method is consistent with the results obtained with natural glycoproteins. To what extent the type of carbohydrate and the size of the polysaccharide groups affect the protective influence is not known, but experiments to clarify this point should be relatively simple in view of the convenient method available for preparation of glycosylated proteins.