Proteins of developing, mature and germinating seeds of phaseolus vulgaris

Abstract

A number of methods have been used to extract, purify and characterise the major storage proteins of dry seeds of Phaseolus vulgaris L. cv. 'Seafarer'. Four fractions, which together account for the majority of the proteins solubilised by alkaline salt extractants and separated by pulyacrylamide gel electrophoresis, ' are described. The predominant protein, accounting for about 60% of the total protein content of the seed, is a vicilin-like protein, and is composed of two subunits, with molecular weights 50,000 and 47,000. A second protein fraction, prepared by zonal isoelectric precipitation, is a legumin-like protein; a third fraction was found to agglutinate erythrocytes. Amino acid compositions are presented for these protein fractions and their identity with storage proteins prepared in previous studies is discussed. The fourth fraction was not characterised. The protein content of protein bodies prepared by two methods was compared; the method of preparation was found to have a significant effect on the apparent distribution of both storage proteins and trypsin inhibitor activity. Variations in the distribution of storage proteins within the cotyledon are also described. The formation of storage protein during seed development and its subsequent mobilisation during seed germination was followed by SDS gel electrophoresis. Changes in proteolytic activity during germination were determined and attempts were made to identify the in vivo location of storage protein hydrolysis and the possible effect of endogenous inhibitors on this process.