Intrinsic catalytic activity of procarboxypeptidase A. A kinetic study using fluorine analogues.
Bovine procarboxypeptidase A displays substantial catalytic activity toward halogenated acyl-amino acids, the most active of which is trifluoroacetyl-L-phenylalanine (TFAc-L-Phe). Though this activity is not as great as for the native enzyme, it is quite substantial and far beyond the range of adventitious activation. Both DL-benzylcuccinate and beta-phenylpropionate inhibit zymogen hydrolysis of TFAc-L-Phe, the former with a K1 of 4.1 micrometer and the latter, 900 micrometer (a value much higher than the corresponding enzyme). Apo procarboxypeptidase A will also hydrolyze TFAc-L-Phe, presumably the polarization of the carbonyl carbon being accomplished by the fluorine atoms in the absence of a specific metal ion. That this is not entirely the metal ion function is indicated by the fact that rate enhancements follow the order manganese procarboxypeptidase A approximately zinc procarboxypeptidase greater than apo-procarboxypeptidase. The results indicate considerable similarities for the zymogen-enzyme pair in terms of catalytic groups, pH dependence, specificity and the nature of their transition state binding sites. Some changes in the substrate or inhibitor binding sites are noted.
Intrinsic catalytic activity of procarboxypeptidase A. A kinetic study using fluorine analogues. Bovine procarboxypeptidase A displays substantial catalytic activity toward halogenated acyl-amino acids, the most active of which is trifluoroacetyl-L-phenylalanine (TFAc-L-Phe). Though this activity is not as great as for the native enzyme, it is quite substantial and far beyond the range of adventitious activation. Both DL-benzylcuccinate and beta-phenylpropionate inhibit zymogen hydrolysis of TFAc-L-Phe, the former with a K1 of 4.1 micrometer and the latter, 900 micrometer (a value much higher than the corresponding enzyme). Apo procarboxypeptidase A will also hydrolyze TFAc-L-Phe, presumably the polarization of the carbonyl carbon being accomplished by the fluorine atoms in the absence of a specific metal ion. That this is not entirely the metal ion function is indicated by the fact that rate enhancements follow the order manganese procarboxypeptidase A approximately zinc procarboxypeptidase greater than apo-procarboxypeptidase. The results indicate considerable similarities for the zymogen-enzyme pair in terms of catalytic groups, pH dependence, specificity and the nature of their transition state binding sites. Some changes in the substrate or inhibitor binding sites are noted.