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Lorena G. Fenoll, Francisco García-Molina, María A. Gilabert, Ramón Varón, Pedro A. García-Ruiz, José Tudela, Francisco García-Cánovas, José N. Rodríguez-López
Interpretation of the reactivity of peroxidase compound II with phenols and anilines using the Marcus equation
Keywords: Anilines, ascorbic acid, Marcus equation, peroxidase, Phenols, Reaction mechanism
The catalytic cycle of heme peroxidases involves three processes: the formation of compound I, its conversion to compound II and regeneration of the native enzyme. Each of the processes consists of a reversible binding stage followed by an irreversible transformation stage. Our group has proposed a continuous, sensitive and reliable chronometric method for measuring the steady-state rate of peroxidase activity. Furthermore, we have derived an analytical expression for the steady-state rate and simplified it, taking into consideration the experimental values of the rate constants of some stages previously determined by other authors in stopped-flow assays. We determined the value of the constant for the transformation of a series of phenols and anilines by compound II, and found that it involves a deprotonation step and an electron transfer step. Study of the solvent deuterium isotope effect on the oxidation of phenol revealed the non-rate-limiting character of the deprotonation step in a proton inventory study. Usage of the Marcus equation showed that the electronic transfer step is rate-limiting in both cases, while phenols and anilines were oxidised at different rates for the same potentials. This can be attributed to the shorter electron-tunnelling distance for electron transfer to the iron ion in the phenols than in the anilines.
Biological Chemistry, Walter de Gruyter
Print ISSN: 1431-6730
Volume: 386, 04/2005
Pages: 351 - 360