| Abstract: | Bovine procarboxypeptidase A exhibits intrinsic hydrolytic activity toward haloacyl amino acids (Behnke and Vallee, 1972), as well as toward conventional peptide and ester substrates for carboxypeptidase A (Bezzone, 1974; Uren and Neurath, 1974). The kinetics of hydrolysis of a series of such substrates by native procarboxypeptidase has now been examined in detail in order to ascertain the extent to which the binding and catalytic sites of carboxypeptidase preexist inthe zymogen. Distinct differences in the substrate binding sites of the zymogen compared with the enzyme are apparent from their respective kinetic profiles as well as from the effects of modifiers on their activities. Substrate activation with the dipeptides BzGly-L-Phe and CbzGly-L-Phe, well known for carboxypeptidase, is exhibited also by the zymogen, but the corresponding substrate inhibition by CbzGly-L-Phe and BzGly-Ophe is absent. Moreover, the substrate inhibition of carboxypeptidase by CbzGlyGly-L-Phe and BzGly-Ophe is replaced by substrate activation in the zymogen... |
