Studies on the Renal Glomerular Basement Membrane

Abstract Digestion of bovine glomerular basement membranes with purified collagenase resulted in the solubilization of over 90% of the carbohydrate and peptide portions. After further digestion of the solubilized material with Pronase, the carbohydrate units, with only a few amino acid residues attached, were isolated by gel filtration and ion exchange chromatography. Characterization of the glycopeptides separated by these fractionation procedures indicated the presence in the basement membrane of two distinct types of carbohydrate units. One type is a disaccharide unit containing glucose and galactose, while the second type is a heteropolysaccharide consisting of galactose, mannose, hexosamines, sialic acids, and fucose, with an average molecular weight of 3500. The carbohydrate of the basement membrane appears to be equally distributed between these two types of units. There are approximately 10 disaccharide units for every heteropolysaccharide unit in the membrane. The carbohydrate-peptide linkage of the disaccharide unit was shown to be a glycosidic linkage involving the hydroxyl group of hydroxylysine, whereas the attachment of the heteropolysaccharide unit to the peptide most likely involves asparagine. Periodate oxidation studies indicated that approximately 70% of the hydroxylysine residues of the basement membrane are involved in the linkage of the disaccharide unit.