Studies of the Oxygenated Compound of Cytochrome Oxidase

Results of rapid reaction experiments indicate that the first observable product formed after the reaction of oxygen with purified reduced cytochrome oxidase is a spectral form which corresponds to that of the oxidized enzyme. latter is then slowly converted to The Compound, or so-called oxygenated form. These observations suggest that Compound is not an intermediate in the cytochrome oxidase-oxygen reaction. Results of spectrophotometric experiments show that what corresponds to Compound can be generated after aeration of the enzyme subsequent to reduction with formamidinesulfinic acid, or after aeration of dithionite-reduced oxidase, even when the reduction has been carried out by anaerobic titration to eliminate excess dithionite. Possible explanations for Compound are (a) a mixture of ferrous and cupric ions, (b) a mixture of ferrous, ferric, and cupric ions, (c) a higher oxidation state of the heme iron, (d) a change in the oxidation-reduction state of groups on the protein other than iron or copper which affect its absorption spectrum, and (e) a configurational change of the oxidase protein that affects the environment of the heme.