Interaction of Asp. melleus Semi-alkaline protease with benzeneboronic acid

Benzeneboronic acid (BBA), a possible transition-state analog for serine proteases, was found to inhibit Asp. melleus semi-alkaline protease [EC 3.4.21.15]. The pH dependence of inhibitor constants was studied by the pH-stat method using N-acetyl-L-tyrosine ethyl ester as a substrate at 25 degrees C. From the pH dependence of the association constant (reciprocal inhibitor constant), a pK value of 6.6, which may be attributable to the catalytic histidine residue of the enzyme, was estimated. The BBA-enzyme interaction was studied kinetically by the temperature-jump method. Apparent association and dissociation rate constants were determined at pH 6.5.