The conformational states of cytochrome oxidase in the mitochondrion.

THE Soret spectrum of "resting" cytochrome oxidase in cytochrome-c depleted mitochondria has been determined. The spectrum obtained is dependent on the rate at which the oxidase is turning over. In the least active preparations, the spectrum is almost pure "oxidized" oxidase. With increasing activity the spectrum is converted to a mixture of "oxidized" and "oxygenated" oxidases. It is concluded that the same conformational differences between the two non-reduced forms that are found in the purified enzyme also occur in these cytochrome-c depleted mitochondria.