THE INVOLVEMENT OF1O2 IN THE INACTIVATION OF MIXED FUNCTION OXIDASE AND PEROXIDATION OF MEMBRANE LIPIDS DURING THE PHOTOSENSITIZED OXIDATION OF LIVER MICROSOMES

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Abstract
Abstract— Dye sensitized photooxidation of rat liver microsomes results in inactivation of mixed function oxidase and peroxidation of the membrane lipids. Both the flavoenzyme NADPH: cytochrome P450 reductase and cytochrome P450 components of the mixed function oxidase were inactivated. Singlet oxygen was responsible for these effects as the inactivation was markedly enhanced if the microsomes were in D2O buffer during the irradiation. Singlet oxygen quenchers or traps also protected the microsomes against enzyme inactivation and lipid peroxidation. Antioxidants, whilst preventing the lipid peroxidation, did not protect cytochrome P450 from inactivation which suggests that lipid peroxidation was not responsible for cytochrome P450 inactivation.