Cotyledonary Storage Proteins in Pisum sativum. I. Molecular Heterogeneity

Abstract

The two storage-protein fractions of pea seeds, legumin and vicilin, have each been resolved electrophoretically on a cellulose acetate gel matrix into multiple molecular species distinguished by electrophoretic mobility and by quantitative or qualitative differences in subunit composition or both. Electrophoretograms of these apparent holoproteins from a range of lines and cultivars were found to be genotype-specific, generally showing three strong bands, together with up to three additional minor bands, assignable to a vicilin series of components. A further three or four bands could be assigned to a legumin series, although the slowest of these showed apparent admixture of certain polypeptides typical of the vicilin fractions. Each putative holoprotein band in both the legumin and vicilin series behaved additively in the electrophoretograms of F1 offspring from reciprocal crosses between lines showing distinct patterns. For comparison with the proteins distinguished electrophoretically on cellulose acetate gels, storage proteins from lyophilized protein bodies were fractionated on the basis of differential solubility at various ionic strengths and pH values. The single legumin and three vicilin fractions obtained by this method showed sedimentation velocities typical of the respective holoproteins. No overlap in the polypeptide composition of legumin with that of vicilin fractions was observed. The components represented in the four fractions accounted for all the major polypeptides in total storage-protein extracts and in the bands eluted from cellulose acetate gels. The distinctive polypeptide pattern and electrophoretic mobility of vicilin fraction 4 identified this protein as a contaminant of slow legumin bands in cellulose acetate gels, and as an additional vicilin species not recognized directly from the electrophoretic analysis.