PROTEIN BODY MEMBRANES OF PHASEOLUS VULGARIS L. COTYLEDONS: ISOLATION AND PRELIMINARY CHARACTERIZATION OF CONSTITUENT PROTEINS

Abstract

Membrane preparations (1·16 g ml−1 average density) produced by osmotic shock from cotyledonary protein bodies of Phaseolus vulgaris were isolated and purified by sucrose density centrifugation. The constituent polypeptides of these membranes were characteristic and different from those of storage proteins and were shown by SDS gel electrophoresis to consist of, in addition to low mol. wt glycolipid‐type material, polypeptides of 16000, 20000, 25000, 30000 and 78000. Of these, the 25000 and the 78000 components appeared to be more tightly associated with the membrane structure than other polypeptides. The 20000, 25000 and 30000 polypeptidea were separated by preparative SDS gel electrophoresis, freed from SDS and extraneous carbohydrates by phenol‐borate (pH 8) partitioning and further purified by chromatography on Bio Gel A 5 m in 5 M guanidine HC1. The 30000 polypeptide was identified by chemical, physical and immunochemical methods as a haemagglutinating globulin lectin. The 25000 polypeptide component bore a superficial resemblance to the so‐called structural protein generally distributed in a great variety of plants and animal membranes. The 20000 polypeptide has not yet been identified with any known Phaseolus vulgaris protein. Copyright © 1979, Wiley Blackwell. All rights reserved