Interpretation of the reactivity of peroxidase compound II with phenols and anilines using the Marcus equation.
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.
Fenoll
Lorena G
LG
Grupo de Investigación Enzimología (GENZ), Departamento de Bioquímica y Biología Molecular-A, Facultad de Veterinaria, Universidad de Murcia, A. Correos 4021, E-30080 Murcia, Spain.
García-Molina
Francisco
F
Gilabert
María A
MA
Varón
Ramón
R
García-Ruiz
Pedro A
PA
Tudela
José
J
García-Cánovas
Francisco
F
Rodríguez-López
José N
JN
D000814:Aniline Compounds / Q000378:metabolism*; D007700:Kinetics; D008956:Models, Chemical; D009195:Peroxidase / Q000737:chemistry* / Q000378:metabolism*; D010636:Phenols / Q000737:chemistry* / Q000378:metabolism*
D000814:Aniline Compounds; D010636:Phenols; D009195:Peroxidase