Biochemical investigations on the seed proteins of a Brazilian variety and mutant of Phaseolus vulgaris

The proteins of the Brazilian beans (Phaseolus vulgaris) cvs Goiano precoce and Carioca and a mutant C-32 (Carioca precoce), obtained after exposure of the parent variety to 60Co gamma irradiation (32 krad), were compared. The storage proteins (globulins) were extracted from mature seeds of Carioca and fractionated by isoelectric precipitation. The two fractions obtained together accounted for most of the alkaline salt soluble proteins separated in polyacrylamide gels by electrophoresis. The predominant protein accounted for about 85% of the total storage protein in the extracts and was vicilin-like protein. This vicilin fraction contained at least two glycoproteins. One of these, the major protein in the seeds, was a cryoprotein and it has been equated with glycoprotein II. The second protein fraction, prepared by zonal isoelectric precipitation, was a legumin-like protein which could be stained only lightly by the PAS reagent. The proportion of the vicilin-like protein to legumin-like protein in seed extracts was about 8:1, as judged by dye binding. The vicilin-like fraction had four subunits with the following molecular weights: 52000, 47000, 32500 and 24000. The legumin-like fraction was dissociated to three subunits: 62500, 37000 and 22500. The content of sulphur amino acids (methionine plus 1/2 cystine) in legumin was greater than in vicilin. The Tris-soluble protein contents of Carioca and of the C-32 (M6) mutant seeds were similar and were lower than that of cv. Goiano precoce seeds. The protein pattern showed in all cases about 14 bands when examined by electrophoresis in a basic gel column system and small differences in at least six bands were detected between the mutant and the Carioca control; they differed from the pattern of the Goiano cultivar. (author)