Can ferricyanide oxidize carbon monoxide-liganded cytochrome a3?

Evidence for the oxidation of CO-liganded cytochrome a3 by ferricyanide has been published recently. These observations conflict with the long-held belief that ferricyanide is thermodynamically incapable of oxidizing the CO complex. The present paper examines the facts on which the earlier idea was based. It is concluded that the earlier evidence did not establish that ferricyanide was incompetent as an oxidant for CO-liganded cytochrome a3.