Studies on the interaction of the components of the mitochondrial electron transfer system

• Main Author: Whittaker, Peter A.
• Published: University of Leicester 1964
• Subjects: 572
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.737045

In this thesis a study has been made of the interaction of the components of the mitochondrial respiratory chain with particular reference to ubiquinone (Coenzyme Q). The results may be summarized as follows:- i) A potentiometric method of measuring the succinate ferricyanide reductase activity of a heart muscle preparation has been described. It has been used to define two sites of reaction of the electron acceptor, potassium ferricyanide with the succinate oxidase respiratory chain. Above 0.6 mM, the reaction of ferricyanide is mainly at the succinate dehydrogenase-non-haem iron level, below this concentration of ferricyanide the main activity is at the cytochrome c level. ii) Non-haem iron function as an electron carrier has been investigated using metal chelating agents as inhibitors of the enzymic reactions of the succinate oxidase system of heart muscle preparations. Three sites of involvement have been tentatively identified. These agree with those suggested by other workers approaching the problem from different angles. The formation of a metal chelate in heart muscle preparation treated with the chelating agent., 2-thenoyltrifluoroacetone has been demonstrated. iii) The function of the lipid cofactor, ubiquinone, in electron transfer processes has been investigated in tightly coupled rat liver mitochondria. Examination of the oxidation-reduction state of the quinone in different metabolic conditions, and in the presence of different uncoupling agents and electron transfer inhibitors by rapid chemical extraction of the intramito- chondrial ubiquinone has reinforced the idea that ubiquinone is an electron carrier. The possibility that ubiquinone is also involved in oxidative phosphorylation has not been eliminated. iv) A newly discovered stimulation of succinate oxidase by ubiquinone homologues in cytochrome c deficient heart muscle preparations is described. The results suggested two possible explanations (a) that the added quinone might by-pass the cytochrome c deficient site or (b) that the electron flux through residual cytochrome c might be increased by the boosting of an inter-chain conductor pathway by the added quinone.