Oxygenation of carbon monoxide by bovine heart cytochrome c oxidase

Cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1), as the terminal enzyme of the mammalian mitochondrial electron transport chain, has long been known to catalyze the reduction of dioxygen to water. We have found that when reductively activated in the presence of dioxygen, the enzyme will also catalyze the oxidation of carbon monoxide to its dioxide. Two moles of carbon dioxide is produced per mole of dioxygen, and similar rates of production are observed for 1- and 2-electron-reduced enzyme. If 13CO and O2 are used to initiate the reaction, then only 13CO2 is detected as a product. With 18O2 and 12CO, only unlabeled and singly labeled carbon dioxide are found. No direct evidence was obtained for a water-gas reaction (CO + H2O----CO2 + H2) of the oxidase with CO. The CO oxygenase activity is inhibited by cyanide, azide, and formate and is not due to the presence of bacteria. Studies with scavengers of partially reduced dioxygen show that catalase decreases the rate of CO oxygenation.