Glycosylation and Deglycosylation of Storage Proteins in Developing Agrostemma githago L. Seeds

Abstract

Summary A 23 kD protein is the major glycoprotein in embryos of Agrostemma githago seeds. This glycoprotein is synthesized by cleavage of a 88 kD protein which is also glycosylated. Because cycloheximide inhibited leucine incorporation considerably more than glucosamine incorporation, glycosylation occurs to some extent post-translationally. Tunicamycin inhibited glycosylation only to a small extent. Since after tunicamycin treatment a small amount of the nonglycosylated form of the 23 kD glycoprotein was present, glycosylation is not necessary for processing and transport of this protein. A small decrease in the relative molecular weight which occurs as a final processing step in the synthesis of two storage proteins of 17 kD and 38 kD, very probably represents a deglycosylation event as was shown by the disappearance of [ 3 H]mannose and [ 3 H]glucosamine label at the appropriate positions on the gel during a chase. By analogy, a small decrease of the relative molecular weight in the synthesis of the 23 kD glycoprotein may be attributed to a partial deglycosylation.