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Abstract
The role of copper of cytochrome oxidase in the electron transfer sequence proposed in vitro was investigated by spectroscopically monitoring the steady-state redox changes of cytochrome c, copper and heme a + a3 of cytochrome oxidase in the perfused rat head. The percent oxidation of copper and cytochrome c in the aerobic-anaerobic transition did not show a straight-line relationship. As compared with copper, cytochrome c was most reduced, followed by heme a + a3. These results suggested that copper first accepted an electron from heme a rather than cytochrome c in the mitochondrial membrane, unlike the electron transfer sequence proposed for purified enzymes. The orientation between cytochrome c and cytochrome oxidase would appear to be controlled primarily by the membrane structure.