Electron Transfer between Cytochrome c and Porphyrins

Article abstract of DOI:10.1021/ja00271a005

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 3.5E8 to 11E8 M^1- s^1- (25 deg C, 0.5M 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.