bcm_1056.qxd

Abstract-Mitochondrial cytochrome c oxidase is able to oxidize various aromatic compounds like o-dianisidine, benzidine and its derivatives (diaminobenzidine, etc.), p-phenylenediamine, as well as amidopyrine, melatonin, and some other pharmacologically and physiologically active substances via the peroxidase, but not the oxidase mechanism. Although specific peroxidase activity of cytochrome c oxidase is low compared with classical peroxidases, its activity may be of physiological or pathophysiological significance due to the presence of rather high concentrations of this enzyme in all tissues, as well as specific localization of the enzyme in the mitochondrial membrane favoring accumulation of hydrophobic aromatic substances

Time-resolved generation of a membrane potential by ba(3) cytochrome c oxidase from Thermus thermophilus - Evidence for reduction-induced opening of the binuclear center

Abstractba3-type cytochrome c oxidase purified from the thermophilic bacterium Thermus thermophilus has been reconstituted in phospholipid vesicles and laser flash-induced generation of a membrane potential by the enzyme has been studied in a μs/ms time scale with Ru(II)-tris-bipyridyl complex (RuBpy) as a photoreductant. Flash-induced single electron reduction of the aerobically oxidized ba3 by RuBpy results in two phases of membrane potential generation by the enzyme with τ values of about 20 and 300 μs at pH 8 and 23°C. Spectrophotometric experiments show that oxidized ba3 reacts very poorly with hydrogen peroxide or any of the other exogenous heme iron ligands studied like cyanide, sulfide and azide. At the same time, photoreduction of the enzyme by RuBpy triggers the electrogenic reaction with H2O2 with a second order rate constant of ∼2×103 M−1 s−1. The data indicate that single electron reduction of ba3 oxidase opens the binuclear center of the enzyme for exogenous ligands. The fractional contribution of the protonic electrogenic phases induced by peroxide in cytochrome ba3 is much less than in bovine oxidase, pointing to a possibility of a different electrogenic mechanism of the ba3 oxidase as compared to the oxidases of the aa3-type

Redox-linked protolytic reactions in soluble cytochrome-c oxidase from beef-heart mitochondria: Redox Bohr effects

A study is presented of co-operative redox-linked protolytic reactions (redox Bohr effects) in soluble cytochrome-c oxidase purified from bovine-heart mitochondria. Bohr effects were analyzed by direct measurement, with accurate spectrophotometric and potentiometric methods, of H+ uptake and release by the oxidase associated with reduction and oxidation of hemes a and a3, Cu(A) and Cu(B) in the unliganded and in the CN- or CO-liganded enzyme. The results show that there are in the bovine oxidase four protolytic groups undergoing reversible pK shifts upon oxide-reduction of the electron transfer metals. Two groups with pK(ox) and pK(red) values around 7 and >12 respectively appear to be linked to redox transitions of heme a3. One group with pK(ox) and pK(red) around 6 and 7 is apparently linked to Cu(B), a fourth one with pK(ox) and pK(red) of 6 and 9 appears to be linked to heme a. The possible nature of the amino acids involved in the redox Bohr effects and their role in H+ translocation is discussed