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Seed Proteins of Common Bean¹

Fractionation of bean (Phaseolus vulgaris L.) cotyledon storage proteins using an improved separation procedure revealed a protein profile in which globulin-I was the major fraction (about 40% of the total cotyledon protein), followed in importance by an alkali-soluble fraction (about 25%) containing glutelin and albumin, free amino acids, ginbulin-2, prolamine, and residue fractions. SDS-acrylamideg el electrophoresis was performed to determine banding patterns of total cotyledon polypeptides and the purity of the fractions. Amino acid analyses using an autoanalyzer were performed on total protein and protein fractions. The alkali-soluble fraction had the highest concentration of methionine (2% of the protein by weight), while the methionine percentage of globulin-1 (0.88%) and albumin (1.0%) was less than that of the respective cotyledons (1.10%). The alkali-soluble and globulin-1 fractions comprised three-fourths of the total cotyledon methionine. Total cotyledon protein was positively correlated with globulin-1, free amino acids, alkali-soluble, and globulin-2 fractions. Significant positive correlations between amount of methionine in the cotyledons and that in the alkalisoluble fraction were also found. This finding suggests that selection for high protein genotypes in which the alkali-soluble fraction is increased should result in improved methionine content. Since quantitative estimation of this fracion is time-consuminga, simplified procedure for determining the amount of protein insoluble in ascorbate-NaCl solution is suitable for identifying strains with large amountos f the alkali-soluble fraction.

Key Words: Protein fractionation • Amino acid composition • Albumin • Globulin-1 • Gloubulin-2 • Prolamine • Alkali-soluble fraction • Free amino acids • SDS-acrylamide gel electrophoresis

² Former graduate research assistant (now research associate) and professor, Dep. of Horticulture, Univ. of Wisconsin, Madison, WI 53706.

Received for publication July 27, 1977.