THE OXIDATION OF EXOGENOUS AND ENDOGENOUS CYTOCHROME C IN MITOCHONDRIA : A Biochemical and Ultrastructural Study

The effect of the nonionic detergent Lubrol on the oxidation of endogenous and exogenous cytochrome c by cytochrome oxidase in intact and fragmented mitochondria was studied. Mitochondria and mitochondrial fragments from liver, kidney, heart, and skeletal muscle have been used. Negatively stained preparations of intact mitochondria showed the particles of Fernández-Morán on the matrix side of their inner membrane system: under these conditions, the oxidation rate of externally added cytochrome c was very high, and it was stimulated very poorly by Lubrol. Mechanical fragmentation of liver mitochondria yielded vesicles with a smooth external profile: also under these conditions, the oxidation of externally added cytochrome c was very high, and poorly stimulated by Lubrol. The oxidation of endogenous cytochrome c was also unaffected by Lubrol. On the other hand, fragmentation of heart and skeletal muscle mitochondria yielded vesicles having numerous particles of Fernández-Morán on their external profiles. Under these conditions, the oxidation of exogenous cytochrome c was low and was markedly stimulated by Lubrol. On the contrary, no activation of the oxidation of endogenous cytochrome c was induced by the detergent. The results indicate a difference in the permeability properties of the two faces of the inner mitochondrial membrane: a permeability barrier for cytochrome c is suggested to exist at the inner face.