Wheat Germ Trypsin Inhibitors. Isolation and Structural Characterization of Single-Headed and Double-Headed Inhibitors of the Bowman-Birk Type1

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Abstract
A number of trypsin inhibitors were isolated from wheat germs by affinity chromatography on immobilized trypsin, gel-filtration, and ion-exchange and reversephase chromatography. These inhibitors were classified into two groups, inhibitors I (Mr= 14,500) and II (Mr = 7,000), based on their molecular sizes. Inhibitors I and II inhibited bovine trypsin stoichiometorically at an enzyme to inhibitor ratio of 2 and 1, respectively. Sequence analysis of these inhibitors indicated a high degree of homology and that inhibitors I had a duplicated structure of inhibitors II. They are highly homologous to double-headed proteinase inhibitors (Bowman-Birk inhibitors) of Leguminosae plants. Inhibitors II are the first example of single-headed inhibitor corresponding to one inhibitory domain of the Bowman-Birk type double-headed inhibitors, which suggests that inhibitors II are relic of an ancestral single-headed inhibitor before the gene-duplication that led to the formation of present-day Bowman-Birk type inhibitors.

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