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Reactivity of photoreduced cytochrome aa3 complexes with molecular oxygen.

ABSTRACT: Cytochrome c oxidase (ox heart cytochrome aa3) is reduced on illumination in the presence of a photocatalyst system containing deazaflavin and EDTA. The photo-reduced enzyme reacts with oxygen at neutral pH to give a form of ferric enzyme, whereas a corresponding sample partially reduced by light in the absence of any photocatalyst reacts with oxygen to give an oxyferri species ('oxygenated' enzyme). Reduction by the photocatalyst system at an alkaline pH value (9.0) also gives rise to fully reduced oxidase (both haem groups ferrous). At these pH values the immediate product after oxygen addition is a species with a 605-606 nm absorption band, not identical with ferrous cytochrome a, but capable of oxidizing added cytochrome c. This intermediate, which is unstable at neutral pH, may be analogous to the 'compound B' obtained by Chance and co-workers [Chance, Saronio & Leigh (1975) J. Biol. Chem. 250, 9226-9237; Chance, Saronio & Leigh (1979) Biochem. J. 177, 931-941] at low temperatures.

SUBMITTER: Nicholls P

PROVIDER: S-EPMC1162806 | biostudies-other | 1981 Mar

REPOSITORIES: biostudies-other

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Project description:Our continuing efforts into developing copper coordination chemistry relevant to dioxygen-processing copper proteins has led us to design and synthesize a cyclotriveratrylene (CTV)-based trinucleating ligand, CTV-TMPA, which employs tetradentate tris(2-pyridylmethyl)-amine chelates (TMPA) for their copper ion binding sites. Binding of three copper ions per CTV-TMPA unit was established by various chemical and spectroscopic methods such as UV-vis and resonance Raman (rR) spectroscopies. The following complexes were observed: A tricopper(I) complex [(CTV-TMPA)Cu(I)(3)](3+) (1), a CO adduct [(CTV-TMPA)Cu(I)(3)(CO)(3)](3+) (1-CO; nu(C=O) = 2094 cm(-1)), a triphenylphosphine adduct [(CTV-TMPA)Cu(I)(3)(PPh(3))(3)](3+) (1-PPh(3)), a tricopper(II) complex [(CTV-TMPA)Cu(II)(3)](3+) (1-Ox), and its tris-monochloride or tris-monobromide adducts. Also, introduction of dioxygen to the -80 degrees C solutions of 1 leads to O(2)-adducts, the first example of a synthetic copper complex which can stabilize a mononuclear Cu(II)-superoxo and dinuclear peroxo species simultaneously within one complex {[Cu] = 1.53 mM in THF: (mu-1,2-peroxo complex, lambda(max) = 543 (epsilon 9650) nm): nu(O-O) = 825 ((Delta(18)O(2)) = -47) cm(-1); nu(Cu-O) = 506 ((Delta(18)O(2)) = -26) cm(-1): (superoxo complex, lambda(max) = 427 (epsilon 3150) nm): nu(O-O) = 1129 ((Delta(18)O(2)) = -60) cm(-1); nu(Cu-O) = 463 ((Delta(18)O(2)) = -27) cm(-1)}. Elemental sulfur reacts reversibly with 1 leading to a (proposed) hexanuclear species [{(CTV-TMPA)Cu(II)(3)}(2)(mu-1,2-S(2)(2-))(3)](6+) (1-S) {lambda(max) = 544 (epsilon 7270) nm}, possessing one dicopper(II)-disulfide structural type: {THF solvent) nu(S-S) = 489 ((Delta(34)S) = -10) cm(-1); nu(Cu-S) = 307 ((Delta(34)S) = -5) cm(-1)}. Derivation of spectroscopic, structural, and chemical conclusions were aided by the study of a close mononuclear analogue with one pyridyl group of the TMPA parent possessing a 6-CH(2)OCH(3) substituent, this being part of the CTV-TMPA architecture.

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Reactivity of photoreduced cytochrome aa3 complexes with molecular oxygen.

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