A kinetic study on the suicide inactivation of peroxidase by hydrogen peroxide.
In the absence of reductant substrates, and with excess H2O2, peroxidase (donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7) shows the kinetic behaviour of a suicide inactivation, H2O2 being the suicide substrate. From the complex (compound I-H2O2), a competition is established between two catalytic pathways (the catalase pathway and the compound III-forming pathway), and the suicide inactivation pathway (formation of inactive enzyme). A kinetic analysis of this system allows us to obtain a value for the inactivation constant, ki = (3.92 +/- 0.06) x 10(-3) x s-1. Two partition ratios (r), defined as the number of turnovers given by one mol of enzyme before its inactivation, can be calculated: (a) one for the catalase pathway, rc = 449 +/- 47; (b) the other for the compound III-forming pathway, rCoIII = 2.00 +/- 0.07. Thus, the catalase activity of the enzyme and, also, the protective role of compound III against an H2O2-dependent peroxidase inactivation are both shown to be important.
Arnao
M B
MB
Departamento de Biología Vegetal (Fisología Vegetal), Universidad de Murcia, Spain.
Acosta
M
M
del Río
J A
JA
Varón
R
R
García-Cánovas
F
F
D006735:Horseradish Peroxidase / Q000037:antagonists & inhibitors*; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007700:Kinetics; D008433:Mathematics; D008962:Models, Theoretical; D011485:Protein Binding; D013053:Spectrophotometry
D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase