Sugar composition of the nephritogenic glycopeptide, nephritogenoside, isolated from rat glomerular basement membrane

Water-soluble and non-dialyzable glycopeptide, nephritogenoside, was isolated from the glomerular basement membrane of normal rats. The yield of the purified nephritogenic glycopeptide from the glomerular basement membrane of 1200 rats was only 17.2 mg. Hexose amounted to 24.3% by weight, and consisted only of glucose. Paper chromatographic studies on the number and length of the carbohydrate chain deduced from strong alkaline cleavage in the presence of sodium borohydride strongly suggested that the carbohydrate chain of the nephritogenic glycopeptide is composed of three glucose residues. This conclusion was supported by the 13C-NMR spectroscopic results. In the paper chromatographic studies on the monosaccharides produced from 3H-labeled oligosaccharide by alkaline degradation and then acid hydrolysis and studies on the 13C-NMR spectrum, it was demonstrated that the saccharide at the reducing terminus is glucose. Thus, the glucose residue at the reducing terminus of the nephritogenoside may be linked directly (probably N-glycosidically) to amino acid, without the intervention of N-acetylglucosamine. The proposed structure of the carbohydrate portion of the nephritogenic glycopeptide, nephritogenoside, is as follows: (formula in text)