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Interpretation of the reactivity of peroxidase compounds I and II with phenols by the Marcus equation
Author(s) -
Folkes Lisa K,
Candeias Luis P
Publication year - 1997
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(97)00792-8
Subject(s) - chemistry , electron transfer , marcus theory , peroxidase , horseradish peroxidase , reactivity (psychology) , phenols , porphyrin , photochemistry , hammett equation , catalysis , electron transport chain , medicinal chemistry , proton coupled electron transfer , catalytic cycle , reaction rate constant , computational chemistry , organic chemistry , kinetics , enzyme , medicine , biochemistry , physics , alternative medicine , pathology , quantum mechanics
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.