The oxygen dependency of the redox state of heme and copper in cytochrome oxidase in vitro.

The oxidation-reduction state of cytochrome oxidase in isolated mitochondria at low oxygen concentrations was measured by the use of leghemoglobin as an oxygen indicator. P50 a + a3 varied with energy state as well as the respiratory rate. In contrast to heme a + a3, copper was slower to reduce than heme a + a3. The P50Cu of 8 x 10(-8)M in State 4 and 7.4 x 10(-8)M in State 3 was independent of both the energy state and the respiratory rate.