Alkaline pH dependence of delta-chymotrypsin-catalyzed hydrolysis of specific substrates.

K(m) (app) and k(cat) for the deltachymotrypsin-catalyzed hydrolysis of N-acetyl-L-tryptophan methyl ester and N-furylacryloyl-L-tryptophanamide were measured as a function of pH and ionic strength. The K(m) (app) values do not increase considerably above pH 9 for delta-chymotrypsin, as is the case with alpha-chymotrypsin. The observed kinetic difference between both enzymes at high pH suggests that the reversible inactivation of alpha-chymotrypsin at alkaline pH may involve the participation of tyrosine 146 or alanine 149 since both residues are present as chain termini in alpha-chymotrypsin but not in delta-chymotrypsin.