AMINO-ACID-COMPOSITION AND SUBUNIT CONSTITUTION OF PROTEIN-FRACTIONS FROM COWPEA (VIGNA-UNGUICULATA L WALP) SEEDS

The protein fractions-albumins, globulins, glutelins, and prolamins-of cowpea (Vigna unguiculata cv. California Blackeye No. 5) seeds were characterized far their subunit constitutions by SDS-PAGE and by amino acid compositions. The abundance of protein fractions was in the following order: globulins, albumins, glutelins, and prolamins. Four major polypeptides with molecular masses of 65, 60, 59, and 50 kDa were separated by SDS-PAGE for globulins. Three of these polypeptides were found to be covalently bound with carbohydrate by the periodic acid-Schiff reagent test. Albumins contained four major polypeptides with molecular masses of 99, 91, 32, and 30 kDa. The alkali-soluble glutelin was mainly composed of polypeptides in the molecular mass range 62-44 kDa. Polypeptides of molecular mass 105, 62, 59, and 54 kDa were found in the prolamin fraction. The cowpea seeds with 24% protein were found to be rich in lysine and leucine but deficient in the sulfur amino acids. Each of the fractions was distinct with respect to its amino acid composition. The glutelin and prolamin fractions were high in essential amino acids compared with the other two fractions.