Glycoprotein Biosynthesis in Cotyledons of Pisum sativum L: Involvement of Lipid-linked Intermediates

Abstract

Particulate preparations from developing cotyledons of Pisum sativum L. cv. Burpeeana catalyze glycosyl transfer from UDP-[(14)C]N-acetylglucosamine and GDP-[(14)C]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-[(14)C]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-[(14)C]N-acetylglucosamine appears to be N,N'-diacetylchitibiosyl 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-[(14)C]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-[(14)C]mannose incorporation, appears to be associated with glycoprotein. The majority of the radioactivity found in the residue fraction labeled from GDP-[(14)C]mannose appears to be associated with oligomannosyl residues.