Glycopeptides from bovine liver basement membrane and plasma membrane

Proteolytic digests of liver plasma-cell membranes from the cow were fractionated to yield two homogeneous glycopeptides and a third preparation about 92% pure. The composition of the two homogeneous glycopeptides made it clear that they were derived from basement membrane material rather than the plasma membrane. Ruminants are unusual in having large amounts of basement membrane in the liver while other animals generally have little or none. Both basement-membrane-derived glycopeptides contained a glucosyl galactosyl disaccharide linked to hydroxylysine, the smaller one contained no other sugar structure but the larger one contained in addition an acidic heterosaccharide, the two chains probably being linked separately to the same molecule. Smith degradation and beta-elimination operations show that this heterosaccharide has an inner structure containing mannose and hexosamine, with the sugars galactose, N-glycollyl-neuraminic acid and fucose situated more peripherally. The amino-acid-heterosaccharide linkage is alkali stable. The third glycopeptide, which may be plasma-membrane-derived, differs from the heterosaccharide described above in that it contains no glucose and contains some O-seryl and O-threonyl amino-acid--sugar linkage. It, too, has a periodate-resistant structure of hexosamine and mannose.