Interpretation of the reactivity of peroxidase compounds I and II with phenols by the Marcus equation.
The catalytic cycle of heme peroxidases involves two reactive states, compound I and compound II. Although their reduction potentials at pH 7 are similar, compound I is in general more reactive towards organic substrates than compound II. The different reactivities have until now remained unexplained. In this study, the reactions of compounds I and II of peroxidase from horseradish with phenols were analyzed using the Marcus equation of electron-transfer. Both reactions exhibit similar reorganization energies, and the different reactivities of the two enzyme states can be ascribed to a higher apparent rate of activationless electron-transfer in the compound I reactions. This can be attributed to the shorter electron-tunneling distance on electron-transfer to the porphyrin radical cation in compound I, compared to electron-transfer to the iron ion in compound II.
Folkes
L K
LK
Gray Laboratory Cancer Research Trust, Mount Vernon Hospital, Northwood, Middlesex, UK.
Candeias
L P
LP
D002384:Catalysis; D006418:Heme / Q000737:chemistry; D007700:Kinetics; D010544:Peroxidases / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*; D013379:Substrate Specificity; D013816:Thermodynamics
D010636:Phenols; D006418:Heme; D010544:Peroxidases