PHOTOINDUCED ELECTRON-TRANSFER FROM ZINC MYOGLOBIN TO BENZOQUINONE STUDIED BY FT-EPR

A Fourier transform (FT) EPR technique has been used to study the phot oinduced 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 transf er occurring between a porphyrin moiety (ZnPP) in myoglobin and BQ. El ectron transfer rate constants, spin-lattice relaxation times of tripl et porphyrin and BQ(-) and magnitudes of chemically induced dynamic el ectron 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 [5,10,1 ,20-tetrakis(4-sulfonatophenyl)porphinato]zinc(II) (ZnTPPS)-B Q system and discussed in terms of protein effects in ZnMb. We conclud ed that electron transfer occurs from the ZnPP moiety to BQ which is l ocated at the surface of myoglobin.