Steady-state kinetics of plasmin- and trypsin-catalysed hydrolysis of a number of tripeptide- p-nitroanilides

Abstract

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 NH 2-terminal α-amino groups (p K = 7.0) shows some inhibitory effect. The reactions of plasmin and trypsin with the p-nitroanilides k c values similar to those normally found with specific ester substrates, indicating that the deacylation steps of the reactions are rate determining.