pH-dependence of photo-induced electron transfer in zinc-substituted sperm whale myoglobin

The electron transfer between the excited triplet state of zinc-substituted sperm whale myoglobin and Cu2+ has been studied by following the decay rate of delayed fluorescence. The Cu2+ bound on the surface of the myoglobin molecule are efficient quenchers of the excited electron state of Zn-myoglobin. Two bimolecular rate constants of quenching (KQ) for every pH investigated have been calculated. The pH-dependence of KQ1 indicates that the protonation of one amino acid residue (His-GH1 (119] is important for the process. Our results support the idea of the common nature of the mechanism of quenching by Cu2+ and oxidation of oxymyoglobin by Cu2+.