Cytochrome c peroxidase activity of bovine heart cytochrome oxidase incorporated in liposomes and generation of membrane potential.

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 X 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 72 mV was registered transiently; this may be physiologically significant in relation to the energy transduction mechanism.