Photoinduced electron transfer from zinc myoglobin to benzoquinone studied by FT-EPR

Abstract

A Fourier transform (FT) EPR technique has been used to study the photoinduced electron transfer from zinc-substituted myoglobin (ZnMb) to 1,4-benzoquinone (BQ). Both porphyrin cation and BQ anion radicals (BQ^-) were observed, which provide direct evidence of an electron transfer occurring between a porphyrin moiety (ZnPP) in myoglobin and BQ. Electron transfer rate constants, spin–lattice relaxation times of triplet porphyrin and BQ^- and magnitudes of chemically induced dynamic electron polarization (CIDEP) due to the triplet mechanism (TM) and the radical pair mechanism (RPM) were evaluated from decay analyses of the FT-EPR signals of BQ^-. These results were compared with those for a [5,10,15,20-tetrakis(4-sulfonatophenyl)porphinato]zinc(II) (ZnTPPS)–BQ system and discussed in terms of protein effects in ZnMb. We concluded that electron transfer occurs from the ZnPP moiety to BQ which is located at the surface of myoglobin.