Interaction of specific amino acid derivatives with dimeric alpha-chymotrypsin

Binding and catalytic activities of dimeric alpha-chymotrypsin from specific amino acid derivatives were investigated with special reference to the equilibrium between active and inactive monomeric forms of this enzyme occurring in a low pH range. The low catalytic activity of the dimeric enzyme towards these specific substrates was revealed to be due to the difficulty in binding of the dimer. However the free tryptophanates and N-acetyl-L-tryptophan, which are slightly smaller (in molecular size) than the above substrates and comparable to the nonspecific phenyl acetate substrates (towards which the dimeric alpha-chymotrypsin showed an distinct catalytic activity in our previous study [J. Biochem. 87, 871-880 (1980)]), were bound to the dimer more strongly than to the monomeric enzyme. Hence they enhanced dimer formation when added at low concentrations.