Isolation and partial characterization of a trypsin inhibitor from wheat endosperm

Trypsin inhibitors were isolated from wheat endosperm, and a major inhibitor (wheat endosperm trypsin inhibitor-I, WETI-I) was purified by ion-exchange chromatographies on CM-Sephadex and SP-Sephadex, gel filtration on Sephadex G-75 and chromatofocusing on Polybuffer exchanger PBE 94. This inhibitor was a polypeptide composed solely of amino acids, and its pI value was 9.35. It was found to be homogeneous in gel electrophoresis and velocity sedimentation. It showed strong inhibition on bovine trypsin but weak inhibition on bovine alpha-chymotrypsin. The molecular weight of the inhibitor was approximately 7,800 as judged from SDS-gel electrophoresis. This finding, along with the trypsin inhibition data, suggested that the inhibitor bound trypsin in the molar ratio of 1:1. Certain other properties of the inhibitor, including amino acid composition and UV spectral characteristics are presented.