Electron transfer between cytochrome c and porphyrins

Abstract

The electron transfer between cytochrome c and several water-soluble porphyrins (ZnTPPS, ZnTMPyP, ZnTPPC, H2TPPS, and H2TMPyP where TPPS is tetrakis(sulfonatophenyl)porphyrin, TMPyP is tetrakis(N-methylpyridyl)porphyrin, and TPPC is tetrakis(carboxyphenyl)porphyrin) has been studied by the method of photoexcitation. For each porphyrin, two rates corresponding to electron transfer from porphyrin triplet to ferricytochrome c and from ferrocytochrome c to porphyrin cation radical are determined. The second-order rate constant increases from 3.5 × 108 to 11 × 108 M-1 s-1 (25°C, 0.5 M ionic strength, pH 7.0) as the driving force ΔE for the reaction increases from 0.54 to 1.06 V. A reorganization energy of 1.0 eV was deduced for the above electron-transfer reactions, when the rates (at infinite ionic strength) are analyzed according to the theories of Marcus and Hopfield. © 1986 American Chemical Society.