Seed reserve-protein glycosylation in an in vitro preparation from developing cotyledons of Phaseolus vulgaris.

A particulate preparation from developing cotyledons of Phaseolus vulgaris L. was incubated with uridine-5'-diphospho-N-acetyl-D-glucosamine (UDP-GlcNAc; [6-(3)H]glucosamine), and by polyacrylamide gel electrophoretic analysis it was shown that the labeled (N-acetyl)glucosamine (GlcNAc) was incorporated into the principal reserve protein of the cotyledons, vicilin, and also into phytohemagglutinin. Some of the labeled product also reacted with antiserum to vicilin from mature seeds. In contrast it was not possible to detect the incorporation of labeled mannose from guanosine-5'-diphospho-D-mannose (GDP-mannose; [U-(14)C]mannose) into either of these proteins by gel-electrophoretic analysis of the mannose-labeled products, but we did observe a low incorporation of mannose into material which reacted with antiserum to vicillin. The predominant glycosylation reaction in vitro was therefore probably a transfer of GlcNAc alone, rather than in combination with mannose as preformed oligosaccharide.