Seed proteins of cowpea, vigna unguiculata (L.) walp.

Abstract

A number of experiments were designed to extract, separate and characterise the major seed proteins of cowpea, Vigna ungiculata (L.) Walp. cv. Prima and to determine their nutritional status "by- carrying out Sulphur-amino acid analyses. Attempts to isolate legumin by various methods were unsuccessful and legumin is either absent or it occurs in small amounts in this cultivar. Three protein subunits made up more than two-thirds of the protein extracted; these had apparent molecular weights 56,200, 53,000 and 40,500. Major subunits and other smaller molecular weight subunits of the total globulins were partially separated by urea-ion-exchange chromatography and characterised. The major subunits are glycopolypeptides and low in sulphur-amino acids. However, some of the smaller molecular weight subunits contain relatively higher levels of these essential amino acids. The time and rate at which various molecular components change during fruit development was also investigated. Seed fresh weight was found to be the best parameter to follow the course of fruit development in cowpea. There was a differential rate of synthesis between globulin subunits and the rate of synthesis of the individual major subunits also varied during seed development. The greatest rate of total globulin synthesis was during the drying-out stage just before maturity. Analyses of the nitrogenous components in the developing pod at different stages indicated that the pod acted as a nitrogen reservoir in the early stages of development. Differences were found in the protein profiles of one cultivar of V. Unguiculata and its wild relatives.