HIGH-MOLECULAR-MASS BOWMAN-BIRK SOYBEAN ISOINHIBITORS - ISOLATION, CHARACTERIZATION AND KINETICS OF THEIR INTERACTION WITH PROTEINASES

Multiple forms of Bowman - Birk soyabean inhibitor have for the first time been isolated from commercial soya flour and purified to homogeneity. Amino acid compositions and isoelectric points of the inhibitors were determined. The isolated inhibitors are shown to be related to classic (M 8000 Da, 2-II) and high molecular mass glycine-rich (M 17 000 Da, 3-II, 5-II) Bowman - Birk inhibitors. The inhibitor (2-II) was found to have two reactive sites and bind trypsin at one centre and alpha-chymotrypsin, cathepsin G and human leukocyte elastase at the other. Rate constants of the complex formation (k(a)) and complex dissociation (k(d)) were determined by following the kinetics of approaching to the steady state in a system including the enzyme, the substrate and various concentrations of the inhibitor.