PHOTOINDUCED REDUCTION OF CYTOCHROME c IN THE PRESENCE OF HYDROPEROXIDE DERIVATIVE OF BIPHENYL

Abstract The photosensitive hydroperoxide derivative of biphenyl (BPP) was synthesized by the ozonolysis of phenanthrene in methanol. When cytochrome c (cyt c ) was illuminated by UVB light in the presence of BPP (BPPUV), it was reduced both under aerobic and anaerobic conditions. The action spectrum of the reduction was consistent with that of photolytic decomposition of BPP. Both gave maximum reactions at wavelengths around 300–310 nm. Electron spin resonance studies, using 5,5-dimethyl-1-pyrroline N -oxide as a spin-trapping reagent, revealed the generation of hydroxyl radicals in the BPPUV system. Product analysis of adamantane oxidation by BPPW also suggested the generation of hydroxyl radicals rather than singlet oxygen. However, the effects of scavengers were complicated. Singlet oxygen scavengers significantly inhibit the reaction while none of the hydroxyl radical scavengers tested was effective in inhibiting the BPPUV-mediated cyt c reduction. Deuterium oxide, which extends the lifetime of singlet oxygen, inhibited rather than enhanced the reaction. Reduction of cyt c was inhibited by salts, and their activities were correlated to the electron-donating nature of the anions. These results suggest that reduction of cyt c is mediated by electron transfer from a light-induced product of BPP, rather than by free hydroxyl radicals or singlet oxygen.