Metabolism of N-Acetylglucosamine and Glucose in Membranes from Lactating Bovine Mammary Tissue

Lactating bovine mammary membranes incorporate N-acetyl- [hydrogen-3] glucosamine from uridine 5’-diphospho-N-acetyl-[hydrogen-3] glucosamine into two glycolipids soluble in chloroform-methanol, 2:1. These glycolipids have been characterized as N-acetylgluco-saminylpyrophosphoryldolichol (I) and N, N’-diacetyl chitobiosylpyrophosphoryldolichol (II); further, I is a precursor of II. Incubation of the membrane preparation with II in the presence of guanosine 5’-diphospho-mannose gives rise to oligosaccharide-lipids with saccharide moieties of 6 to 10 units. Incubation of the membrane preparation with uridine 5’-diphospho-[hydrogen-3] glucose gives rise to the formation of glucosylphosphoryldolichol, a glucosyl-tridecasaccharide-lipid and labeled glycoproteins. The kinetics of glycosyl transfer indicate that at least one or more glucose units of the oligosaccharide-lipid may be derived directly from uridine 5’-diphospho-[hydrogen-3] glucose even though glycosylphosphoryldolichol is an effective donor for its synthesis. The membrane bound glucosyl protein(s) range from 14 to 16,000 daltons, a size distribution that includes the glycosylated form of α-lactalbumin.