Responses of the a3 component of cytochrome c oxidase to substrate and ligand addition

Shaw, Robert W.; Hansen, Raymond E.; Beinert, Helmut

doi:10.1016/0005-2728(78)90017-8

Cited by 34 publications

(30 citation statements)

References 20 publications

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“…Also, when the fully reduced enzyme is reoxidized anaerobically, cytochrome a3 is oxidized before Cu,,. These differences in reduction potentials between the two metal centers have allowed cytochrome a3 to be observed by EPR as a high-spin heme in a state where cytochrome a3 is oxidized while Cu,, is reduced (Shaw et al, 1978). However, it is clear from this work that in the presence of NO, the reduction potential of cytochrome a3 becomes higher than that of Cu,,.…”

Section: Discussionmentioning

confidence: 84%

Reactions of nitric oxide with cytochrome c oxidase

Brudvig¹,

Stevens²,

Chan³

1980

Biochemistry

243

166

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The reactions of nitric oxide (NO) with both oxidized and reduced cytochrome c oxidase are reported. NMR and mass spectroscopy were utilized to determine the products of the reactions; EPR and optical spectroscopy were employed to determine the states of the enzyme produced in each of these reactions. It was found that the enzyme catalyzes the consecutive oxidation and reduction of NO. A different cycle was observed when NO was added to the reduced enzyme, to the oxidized enzyme, or to the oxidized enzyme in the presence of azide. It was possible to observe the state of the enzyme at several points in each of these three cycles by varying the concentration of NO. The reactions of NO all involved a one- or two-electron redox step and could be accounted for by the involvement of only cytochrome a3 and Cua3. On the basis of these results, a mechanism for the reduction of dioxygen by the enzyme is proposed in which cytochrome a3 functions to anchor dioxygen and intermediates while remaining in the ferrous state, whereas Cua3 functions to accept electroins from cytochrome a/Cua and transfer them to dioxygen.

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Section: Discussionmentioning

confidence: 84%

Reactions of nitric oxide with cytochrome c oxidase

Brudvig¹,

Stevens²,

Chan³

1980

Biochemistry

243

166

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“…AA..l, is the corresponding change in the presence of ferricyanide (3 mM) alone. gument for ferrous a3, because this band is also absent under some conditions in which a3 is unambiguously in the ferric state (28). The possibility that compound C is a A-peroxo species with ferric a3 and Cu" (ref.…”

Section: Resultsmentioning

confidence: 99%

Energy-dependent reversal of the cytochrome oxidase reaction.

Wikström¹

1981

Proc. Natl. Acad. Sci. U.S.A.

149

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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.

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“…This is supported by a higher a band intensity and a deeper trough at -580 nm in the experimental spectrum of intermediate 4 ( Figure SD), and the absence of a significant absorption at 655 nm in the spectra of intermediates 3 and 4 (RosCn et Brunori et al, 1979;Armstrong et al, 1983). The pulsed cytochrome oxidase is formed following reduction by dithionite and subsequent oxidation by dioxygen (Antonini et al, 1977;Brunori et al, 1979), but can also be obtained by oxidizing the reduced enzyme by ferricyanide or porphyrexide (Beinert et al, 1976;Beinert & Shaw, 1977;Shaw et al, 1978;Brunori et al, 1981;Armstrong et al, 1983). The form produced by the anaerobic oxidation is also characterized by the generation of the g = 6 signal (Beinert et al, 1976;Shaw et al, 1978), suggesting that CUB is reduced in the pulsed enzyme.…”

mentioning

confidence: 94%

Intramolecular Electron Transfer and Conformational Changes in Cytochrome c Oxidase

Einarsdóttir¹,

Georgiadis²,

Sucheta³

1995

Biochemistry

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The photolysis intermediates of partially and fully reduced CO-bound cytochrome oxidase derivatives were investigated. A gated optical spectrometric multichannel analyzer was used to collect visible and near-infrared transient difference spectra on time scales from nanoseconds to milliseconds. The spectra were analyzed by a singular value decomposition method combined with a global exponential fitting procedure. Global analysis of the mixed-valence CO complex transient difference spectra shows that five intermediates are present with apparent lifetimes of 1.4 microseconds, 4.8 microseconds, 76.7 microseconds, 10.6 ms, and 21.6 ms. The data were fitted to a kinetic model involving a sequential pathway with accompanying equilibria. On the basis of this mechanism, the absorption spectra of the intermediates were determined. The first step, also present in the fully reduced enzyme, is attributed to a conformational change at cytochrome a3. The spectral changes associated with the second step are similar to those expected for 1:1 electron transfer from cytochrome a3 to cytochrome a, except for a higher absorbance between 480 and 550 nm. A comparison of the experimental spectral change associated with this step, (a2+ minus a3+) minus (a3(2+) minus a3(3+), and the calculated spectral change, (a2+ CuA+ minus a3+ CuA2+) minus a3(2+) CuB+ minus a3(3+) CuB2+), allowed extraction of the absorbance spectrum of CuA2+ in the 480-550 nm region. The spectral change associated with the third step is consistent with the oxidation of cytochrome a. A decrease in the 830 nm band on the same time scale indicates that the electron acceptor is CuA. The data also suggest that the redox state of CuB significantly affects the absorption spectrum of oxidized cytochrome a3 in the visible region. The two processes on a millisecond time scale are attributed to CO recombination and intramolecular electron transfer.

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Responses of the a3 component of cytochrome c oxidase to substrate and ligand addition

Cited by 34 publications

References 20 publications

Reactions of nitric oxide with cytochrome c oxidase

Reactions of nitric oxide with cytochrome c oxidase

Energy-dependent reversal of the cytochrome oxidase reaction.

Intramolecular Electron Transfer and Conformational Changes in Cytochrome c Oxidase

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