Carbohydrate structure of glycopeptides isolated from an hepatic membrane-binding protein specific for asialoglycoproteins.

Two variant glycopeptide constituents of an hepatic membrane protein responsible for the clearance of circulating asialoglycoproteins have been isolated and characterized. Their relative abundance has been estimated to be 14 and 2 mol, respectively, per mol of intact protein. The larger component, glycopeptide I, is comprised of sialic acid, galactose, mannose, glucosamine, and aspartic acid in a molar ratio of 3:3:2:5:1. The smaller neutral fraction contains only two sugars and the molar relationship of mannose, glucosamine, and aspartic acid is 8:2:1. Based on the results of sequential digestion with specific glycosidases and periodate degradation, a carbohydrate sequence for both glycopeptides is proposed.