Biosynthesis of lipid-linked oligosaccharides and glycoprotein in aorta: stimulation by acceptor lipids isolated from liver.

Abstract

An acidic glycolipid fraction was isolated from porcine liver and partially purified on DEAE-cellulose. This material markedly stimulated the incorporation of mannose from GDP-[14C]mannose into lipid-linked oligosaccharides and into glycoprotein, but did not stimulate incorporation into the mannosyl-phosphoryl-polyprenol. The products formed from GDP-[14C]mannose in the presence of acceptor lipid were a series of lipid-linked oligosaccharides of mannose and N-acetylglucosamine (GlcNAc) which differ from each other in the size of the oligosaccharide moieties. The acceptor lipid fraction was partially characterized in terms of its carbohydrate composition by mild acid hydrolysis and reduction with NaB3H4. The [3H]sugars were then separated into a number of monosaccharides and oligosaccharides by paper chromatography. Strong acid hydrolysis of 2 of the larger oligosaccharides released from the acceptor lipid followed by reduction with NaB3H4 gave [3H]mannitol and [3H]GlcN-ol in ratios of 2.8:2 and 3.8:2, indicating that these compounds probably were penta- and hexasaccharides. In addition, GlcNAc was shown to be at the reducing terminus and .alpha.-linked mannose at the nonreducing ends of the molecules. The acceptor lipid fraction is probably composed of oligosaccharides of (Man)n .fwdarw. GlcNAc .fwdarw. GlcNAc, attached to a polyprenol through a pyrophosphoryl linkage.