The role of glycosylation in storage-protein synthesis in developing pea seeds

Intact pea (Pisum sativum L.) cotyledons were incubated with [(14)C]glucosamine at several stages of seed development and the resultant radioactive proteins were analysed by gel electrophoresis combined with immunoaffinity chromatography and sucrose gradient fractionation. Glucosamine was incorporated into at least five vicilin polypeptides (approx. molecular weight 70,000; 50,000, two components; 14,000, two components). No incorporation was detected into the subunits of legumin. Tunicamycin at 50 μg/ml largely inhibited glucosamine incorporation but had little effect on the incorporation of (14)C-labelled amino acids into cotyledon proteins, including vicilin. The assembly of vicilin polypeptides into full-sized protein oligomers (7-9 S) was also unaffected by tunicamycin. Chromatography on concanavalin A confirmed that glycosylation of cotyledon proteins was inhibited by tunicamycin. It is concluded that glycosylation of most cotyledonary proteins involves lipid-linked sugar intermediates, but that glycosylation itself is not an essential step in the synthesis of vicilin polypeptides nor in their assembly into oligomers.