The inhibition of certain mitochondrial enzymes by fatty acids oxidized by ultraviolet light or ascorbic acid

Abstract

1. 1. The relation between lipide oxidation and the activity of succinoxidase, choline oxidase, and aminoxidase of rat liver mitochondria has been examined following ultraviolet irradiation, incubation of mitochondria with ultraviolet-irradiated methyl linolenate and methyl linoleate, and incubation with ascorbic acid. 2. 2. Ultraviolet irradiation of mitochondria produced an oxidation of lipide which was directly proportional to the period of irradiation. Succinoxidase and choline oxidase were inhibited in direct proportion to the extent of lipide oxidation. Incubation of irradiated mitochondria with reduced glutathione gave a partial (< 33 %) restoration of succinoxidase activity. 3. 3. Incubation of mitochondria with ascorbic acid resulted in an inhibition of succinoxidase, choline oxidase, and aminoxidase which was directly proportional to lipide oxidation, as in the case of ultraviolet irradiation. Liver slices incubated with ascorbic acid also showed an increased lipide oxidation and decreased succinoxidase activity. 4. 4. Succinoxidase was inhibited by ultraviolet-irradiated methyl linolenate and its water-soluble oxidation products. The unoxidized ester had little or no effect. Methyl linolenate and methyl linoleate oxidized to the same degree by ultraviolet irradiation had equal inhibitory action on succinoxidase. 5. 5. The results indicate that the effects of ultraviolet light on cells may be mediated in part by the oxidation products of lipide constituents.