Interpretation of the reactivity of peroxidase compound II with phenols and anilines using the Marcus equation

• Published in: Biological chemistry Vol. 386; no. 4; pp. 351 - 360
• Main Authors: Fenoll, Lorena G., García-Molina, Francisco, Gilabert, María A., Varón, Ramón, García-Ruiz, Pedro A., Tudela, José, García-Cánovas, Francisco, Rodríguez-López, José N.
• Format: Journal Article
• Language: English
• Published: Germany Walter de Gruyter 01.04.2005
• Subjects: Aniline Compounds - metabolism; anilines; ascorbic acid; Kinetics; Marcus equation; Models, Chemical; peroxidase; Peroxidase - chemistry; Peroxidase - metabolism; phenols; Phenols - chemistry; Phenols - metabolism; reaction mechanism
• ISSN: 1431-6730; 1437-4315
• DOI: 10.1515/BC.2005.042

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.