Cytochrome c Peroxidase Activity of Bovine Heart Cytochrome Oxidase Incorporated in Liposomes and Generation of Membrane Potential1

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Abstract
Cytochrome oxidase vesicles catalyzed the peroxidatic oxidation of ferrocytochrome c . The maximal peroxidase activity in the absence of an uncoupling agent was 9.8 mol ferrocytochrome c oxidized/(s·mol heme a ), indicating a 5-fold activation compared with the soluble enzyme system. The peroxidase activity was further enhanced 1.2 to 2.1 times upon addition of an uncoupler, carbonyl cyanide p -trifluoromethoxyphenyl hydrazone. The stoichiometry of the reduction of hydrogen peroxide by ferrocytochrome c was established to be 1:2, indicating water formation. Potassium cyanide (0.14 mM) completely inhibited the peroxidase activity. The inhibition by 1 mM CO was 40–77% depending on the energized state of cytochrome oxidase vesicles, but in contrast, 85% inhibition was observed with the soluble enzyme. In the energized state the enzyme showed a slightly lower affinity for CO than in the deenergized state. Coupled with the peroxidase activity, a membrane potential of 72mV was registered transiently; this may be physiologically significant in relation to the energy transduction mechanism.