Amino Acid Sequences of Two Trypsin Inhibitors from Winged Bean Seeds (Psophocarpus tetragonolobus (L)DC.)

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Abstract
The trypsin inhibitor (WTI-1) purified from winged bean seeds is a Kunitz type protease inhibitor having a molecular weight of 19,200. WTI-1 inhibits bovine trypsin stoichiometncally, but not bovine a-chymotrypsin. The approximate Ki value for the trypsin-inhibitor complex is 2.5 × 10−9M. The complete amino acid sequence of WTI-1 was determined by conventional methods. Comparison of the sequence with that of soybean trypsin inhibitor (ST1) indicated that the sequence of WTI-1 had 50% homology with that of STI. WTI-1 was separated into 2 homologous inhibitors, WTI-1A and WTI-1B, by isoelectric focusing. The isoelectric points of WTI-1A and WTI-1B were 8.5 and 9.4, respectively, and their sequences were presumed from their amino acid compositions.