STEADY-STATE KINETICS OF PLASMIN-CATALYZED AND TRYPSIN-CATALYZED HYDROLYSIS OF A NUMBER OF TRIPEPTIDE-PARA-NITROANILIDES

The steady-state kinetics of plasmin- (EC 3.4.21.7) and trypsin-catalysed (EC 3.4.21.4) hydrolysis of Bz-l-Phe-Val-Arg-pNA, Bz-d-Phe-Val-Arg-pNA, l-Phe-Val-Arg-pNA, d-Phe-Val-Arg-pNA and d-Val-Leu-Lys-pNA were investigated in the pH range 6-9. The pH dependences of the kinetic parameters correspond with the effects of catalytically essential ionizations in the enzymes, except for reactions with l- and d-Phe-Val-Arg-pNA, in which protonation of the NH2-terminal α-amino groups (pK = 7.0) shows some inhibitory effect. The reactions of plasmin and trypsin with the p-nitroanilides kc values similar to those normally found with specific ester substrates, indicating that the deacylation steps of the reactions are rate determining. © 1979.