Membranes of Protein Bodies. II. Detection and Partial Characterization of Membrane Glycoproteins

The synthesis of organelle proteins was studied in cotyledons of Cucumis sativus. Protein constituents of protein-body membranes were shown to be synthesized and assembled, at a stage characterized by mobilization of the storage globulin. Besides L-[35S]methionine various labelled hexoses were incorporated into protein bodies of cucumber cotyledons. While D-[U-14C] glucose functioned as precursor of a broad spectrum of glycoproteins, D-[6-3H]glucosamine was selectively incorporated into four glycoproteins of the protein-body membrane. Labelled galactose and mannose, respectively, were preferentially transferred into another set of membrane glycoproteins. The four glycoproteins revealed by labelling with glucosamine were solubilized and purified by chromatography on concanavalin-A-Sepharose.