Characteristics of the proteins of the tubers of winged bean (Psophocarpus tetragonolobus (L.) DC)

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Abstract
The crude protein content (amino acid Nx6.25) of six varieties of Psophocarpus tetragonolobus tuber varied from 12.7 to 16.9%. Free amino acids and low molecular weight peptides account for about 40% of this crude protein value. The non‐dialysable protein content of winged bean tuber is therefore less than previously assumed, but is still relatively high for a tuber crop. The amino acid contents of the tuber varieties were similar and nutritionally acceptable, except for the sulphur containing amino acids. Fresh tubers showed trypsin and chymotrypsin inhibitory activity and haemagglutinin activity. The inhibitor levels showed little variation but differences in the levels of haemagglutinin activity were found. On SDS‐polyacrylamide gels the tuber proteins revealed a simple subunit pattern of two major polypeptides of Mr 30000 and 20000. Fractionation of the tuber proteins showed that the inhibitors and haemagglutinins comprise about 35% of the tuber protein. In addition, three acidic protein (about 12% of tuber protein), three basic proteins (ca. 34% of tuber protein) and a minor component (Mr∼10000) with a high cystine content (11 residue %) were identified.