Energy-dependent reversal of the cytochrome oxidase reaction.

Abstract

Energization of isolated rat liver mitochondria with ATP under conditions in which cytochrome c is poised in a highly oxidized state shifts the state of cytochrome oxidase (cytochrome c oxidase; ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) from fully oxidized to two new spectroscopically distinguishable states depending on the applied phosphorylation potential and redox potential at cytochrome c. Both new states are spectrally similar or identical to two previously described intermediates in the reaction between reduced enzyme and O2. The data suggest that the energy-dependent transitions are due to reversed electron transfer from water to ferricytochrome c linked to accumulation of intermediates of O2 reduction at the catalytic heme a3/copper center. Titrations with redox potential indicate that each transition is a one-electron step, a finding that would identify the second observed compound as enzyme-bound peroxide or its equivalent. This is consistent with this compound being spectrally identical to "Compound C," previously described as the reaction product between half-reduced oxidase (two electrons) and O2. On the basis of these data a catalytic scheme of O2 reduction is proposed for the heme a3/copper center of cytochrome oxidase.

Structures and Proton-Pumping Strategies of Mitochondrial Respiratory Enzymes

“…Addition of a third electron from ferrocytochrome c yields species F, the ferryl form of the enzyme. This species has a band in the optical absorption difference spectrum at 580 nm (134,139,140) and shows an Fe(IV)-oxo stretch in the resonance Raman spectrum at 785 cm −1 (51,89,125). Given the participation of the tyrosyl radical at Y244, the electron used to form the F intermediate likely reduces the tyrosyl radical back to tyrosine.…”

“…Species A then reacts further to yield intermediate P (Compound C, peroxo form), originally assumed to be a peroxo species. This form has also been generated independently from the addition of hydrogen peroxide to oxidized or reduced enzyme (12,140,141), or by the partial reversal of dioxygen chemistry under conditions of high thermodynamic driving force in the reverse direction SCHULTZ CHAN (134,136). It is characterized by an absorption maximum at 607 nm in the optical difference spectrum of the enzyme.…”

Computational study of the activated O H state in the catalytic mechanism of cytochrome c oxidase

“…1C). Low-temperature work by Chance et al (13) identified the O 2 adduct of heme a 3 (compound A), and partial reversal of the catalytic reaction in mitochondria (14) helped to establish the subsequent intermediates P and F, both of which turned out to have heme a 3 in the ferryl state (1,2,15,16). A conserved tyrosine in the BNC is covalently bonded to one of the three histidine ligands of Cu B , and forms a neutral tyrosine radical in state P M (Fig.…”

How I became a biochemist

“…(Tony) Crofts helped me to realize that this could mean that the oxidase reaction might, in fact, be coupled to proton translocation across the mitochondrial membrane, which was the prelude to the discovery of the oxidase as a proton pump. This work also led to the later discovery in 1981 that the oxidase reaction is reversible, which identified some of the key intermediates of the reaction with O 2 (14). Moreover, data by Martin Brand (in 1976 a postoc with Albert Lehninger in Baltimore) indicated that the H 1 /e 2 stoichiometry of proton translocation by the respiratory chain might be higher than anticipated from Mitchell's original notion of chemiosmotic redox loops (15), and as reported by Moyle and Mitchell.…”