Glycoprotein Biosynthesis in Cotyledons of Pisum sativum L

Abstract

Particulate preparations from developing cotyledons of P. sativum L. cv. Burpeeana catalyze glycosyl transfer from UDP-[14C]N-acetylglucosamine and GDP-[14C]mannose. Radioactivity is transferred to lipid components soluble in chloroform-methanol (2:1) and chloroform-methanol-water (1:1:0.3) and into a water-insoluble and lipid-free residue. The chloroform-methanol-soluble component formed from GDP-[14C]mannose appears to be a mannosyl lipid, whereas the chloroform-methanol-water-soluble fraction is probably a mixed oligosaccharide-lipid containing N-acetylglucosamine and mannose residues. The chloroform-methanol-soluble component formed from UDP-[14C]N-acetylglucosamine appears to be N,N''-diacetylchitobiosyl lipid, which may be incorporated with mannose to form the chloroform-methanol-water-soluble mixed oligosaccharide lipid. The oligosaccharide lipid appears to function as a precursor for the transfer of the oligosaccharide to the peptide moiety in the formation of the glycoproteins. The bulk of the radioactivity, arising from UDP-[14C]N-acetylglucosamine, incorporated into the insoluble residue, is associated with glycoprotein. In contrast only a small percentage of radioactivity in the insoluble residue, arising from GDP-[14C]mannose incorporation, appears to be associated with glycoprotein. The majority of the radioactivity found in the residue fraction labeled from GDP-[14C]mannose appears to be associated with oligomannosyl residues.