Bifunctional inhibitor of α-amylase/trypsin from wheat grain

A trypsin inhibitor, isolated from whole-wheat grain (Triticum aestivum L.) by the method of biospecific chromatography on trypsin-Sepharose, was potent in inhibiting human salivary alpha -amylase. The bifunctional alpha -amylase/trypsin inhibitor was characterized by a narrow specificity for other alpha -amylases and proteinases. The high thermostability of the inhibitor was lost in the presence of SH group-reducing agents. The inhibitor-trypsin complex retained its activity against alpha -amylase. The inhibitor- alpha -amylase complex was active against trypsin. Studies of the enzyme kinetics demonstrated that the inhibition of alpha -amylase and trypsin was noncompetitive. Our results suggest the existence of two independent active sites responsible for the interaction with the enzymes.