The oxidized forms of cytochrome oxidase

Abstract

Ferric cytochrome oxidase (Soret max. 418 mμ) and "oxygenated" cytochrome oxidase (Soret max. 428 mμ) carry the same number of oxidizing equivalents (two per heme a) available for the oxidation of ferrous cytochrome c. "Oxygenated" oxidase can be formed by the aerobic oxidation of a3+ + a32+CO and therefore the difference from ferric cytochrome oxidase resides in the a3 moiety of the enzyme. When reductant is added to ferric oxidase aerobically, a transient formation of a2+a33+ occurs but at later times the dominant species in the steady state is "oxygenated" oxidase. It is suggested that the reason for the inhibition of electron flow between a2+ and a33+ may be either in conformational restraints or in the redox state of the associated copper. No such block is apparent in the reduction of "oxygenated" oxidase.