Studies on electron transport and energy-linked reactions in beef heart mitochondria and Escherischia coli

The work described in this thesis was concerned primarily with the possible role of quinones in mitochondrial and bacterial reactions. In this respect electron transport and energy-linked reactions were both examined and the major sources of material used for this purpose were beef heart and Escherichia coli. Various approaches were utilized namely, studies with inhibitors, extraction-reactivation experiments, ultraviolet irradiation techniques and quinone deficient mutants. \n \nAn extensive study was made of the effect of piericidin A, which had been proposed as a ubiquinone analogue, on various bacterial and mitochondrial reactions. It was shown that piericidin was acting at the same site as rotenone in the NADH dehydrogenase region of the respiratory chain of beef heart mitochondria. The possible nature, concentration and specificity of this site was examined. At high concentrations piericidin also inhibited succinate oxidation, possibly due to damage of the mitochondrial membrane system. The effect of piericidin on various other mitochondrial and bacterial reactions was also described. Of particular interest was the inhibition by piericidin of the energy-dependant reduction of NADP+ by NADH in both beef heart submitochondrial particles and small particles derived from E. coli. \n \nThe ATP-dependant reduction of NADP+ by NADH and the ATP-dependant reduction of NAD+ by succinate catalysed by E. coli small particles were both fully characterised. \n \nExtraction techniques were used for studying electron transport and energy-linked reactions in beef heart submitochondrial particles. Reactivation of NADH oxidation, succinate oxidation and the energy-linked reduction of NADP+ by NADH to pentane extracted particles was achieved by the addition of ubiquinone homologues at concentrations equal to those originally present in the particles. The reactions had the same sensitivity to inhibitors of electron transport and oxidative phosphorylation as the normal reactions in unextracted particles. \n \nExtraction techniques, ultraviolet irradiation and ubiquinone deficient mutants were used to study the role of quinones in electron ,transport and energy-linked reactions in E. coli. The results obtained were discussed fully in Chapter VI. \n