REDOX TRANSITIONS BETWEEN OXYGEN INTERMEDIATES IN CYTOCHROME-C-OXIDASE

Some intermediates in the reduction of O-2 to water by cytochrome-c ox idase have been characterized by optical, Raman, and magnetic circular dichroism spectroscopy. The so-called ''peroxy'' (P) and ''ferryl'' ( F) forms of the enzyme, which have been considered to be intermediates of the oxygen reaction, can be generated when the oxidized enzyme rea cts with H2O2, or when the two-electron reduced (''CO mixed-valence'') enzyme reacts with O-2. The structures as well as the overall redox s tates of P and F have recently been controversial, We show here, using tris(2,2'-bipyridyl) ruthenium(LI) as a photoinducible reductant, tha t one-electron reduction of P yields F, and that one-electron reductio n of F yields the oxidized enzyme. This confirms that the overall redo x states of P and F differ from the oxidized enzyme by two and one ele ctron equivalents, respectively. The structures of the P and F states are discussed.