Mechanism of proton translocation by the respiratory oxidases. The histidine cycle

Wikström, Mårten; Bogachev, Alexander V.; Finel, Moshe; Morgan, Joel E.; Puustinen, Anne; Raitio, Mirja; Verkhovskaya, Marina; Verkhovsky, Michael I.

doi:10.1016/0005-2728(94)90093-0

Cited by 133 publications

(95 citation statements)

References 25 publications

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“…4A illustrates how protons could be taken up and released in the wild-type oxidase to accomplish oxygen reduction and proton pumping in a manner consistent with mutagenesis results and theoretical considerations suggesting separate pumping and substrate proton pathways [3,17]. The mutation of D132 is depicted in Fig.…”

Section: Fatty Acid Stimulation Of Activity and Restoration Ofsupporting

confidence: 60%

Fatty acids stimulate activity and restore respiratory control in a proton channel mutant of cytochrome c oxidase

Fetter¹,

Sharpe²,

Qian³

et al. 1996

FEBS Letters

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either an alanine (DI32A) or an asparagine (D132N) strongly diminishes oxygen reduction activity and abolishes proton pumping. D132 is a substantial distance from the oxygen-reactive site and mutation of the residue does not perturb the spectral properties of the metal centers [4]. Similar effects are seen when the corresponding residue in Escherichia coli cytochrome bo3 is mutated [5,6]).Another effect of the D132N/A mutations is that the reconstituted enzymes show anomalous responses to uncouplers and ionophores [4]. Valinomycin and CCCP, both singly and in combination, inhibit instead of stimulating turnover in reconstituted enzyme. The ionophores do not inhibit the purified enzyme directly and the oxygen reduction activity shows a similar decrease with increasing pH as wild-type, indicating that the inhibition is likely caused by changes in membrane potential (A~) and/or pH gradient (ApH) [4]. An understanding of these responses might clarify the pumping process itself. The present paper will show that (i) a normal membrane potential is formed by COV containing mutant enzyme and (ii) the defect of the D132A/N mutations can partially be overcome by addition of free fatty acids. The fatty acids also rectify the anomolous responses to uncouplers and ionophores, but repair of proton pumping has not been demonstrated. Materials and methods

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Section: Fatty Acid Stimulation Of Activity and Restoration Ofsupporting

confidence: 60%

Fatty acids stimulate activity and restore respiratory control in a proton channel mutant of cytochrome c oxidase

Fetter¹,

Sharpe²,

Qian³

et al. 1996

FEBS Letters

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“…His I-334, a Cu B ligand, has also been proposed to act as a residue whose protonation state is coupled to the BNC redox state. Earlier work by Wikström suggested that this His might break its bond to Cu B and be doubly protonated in a His shuttle (38). More recently, Stuchebrukhov proposed that the His becomes a fully deprotonated imidazolate, coexisting with a hydroxyl group on Cu B in the fully oxidized state (39).…”

Section: Resultsmentioning

confidence: 99%

Calculated Proton Uptake on Anaerobic Reduction of CytochromecOxidase: Is the Reaction Electroneutral?

2006

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Cytochrome c oxidase is a transmembrane proton pump that builds an electrochemical gradient using chemical energy from the reduction of O 2 . Ionization states of all residues were calculated with Multi-Conformation Continuum Electrostatics (MCCE) in seven anaerobic oxidase redox states ranging from fully oxidized to fully reduced. One long-standing problem is how proton uptake is coupled to the reduction of the active site binuclear center (BNC). The BNC has two cofactors: heme a 3 and Cu B . If the protein needs to maintain electroneutrality, then 2 protons will be bound when the BNC is reduced by 2 electrons in the reductive half of the reaction cycle. The effective pK a s of ionizable residues around the BNC are evaluated in Rhodobacter sphaeroides cytochrome c oxidase. At pH 7, only a hydroxide coordinated to Cu B shifts its pK a from below 7 to above 7 and so picks up a proton when heme a 3 and Cu B are reduced. Glu I-286, Tyr I-288, His I-334, and a second hydroxide on heme a 3 all have pK a s above 7 in all redox states, although they have only 1.6-3.5 ∆pK units energy cost for deprotonation. Thus, at equilibrium, they are protonated and cannot serve as proton acceptors. The propionic acids near the BNC are deprotonated with pK a s well below 7. They are well stabilized in their anionic state and do not bind a proton upon BNC reduction. This suggests that electroneutrality in the BNC is not maintained during the anaerobic reduction. Proton uptake on reduction of Cu A , heme a, heme a 3 , and Cu B shows ≈2.5 protons bound per 4 electrons, in agreement with prior experiments. One proton is bound by a hydroxyl group in the BNC and the rest to groups far from the BNC. The electrochemical midpoint potential (E m ) of heme a is calculated in the fully oxidized protein and with 1 or 2 electrons in the BNC. The E m of heme a shifts down when the BNC is reduced, which agrees with prior experiments. If the BNC reduction is electroneutral, then the heme a E m is independent of the BNC redox state.Heme-copper oxidases are the terminal electron acceptors in anaerobic organisms. These transmembrane proteins reduce dioxygen and convert the released chemical energy into an electrochemical gradient, across the eukaryotic mitochondrial membrane or the bacterial cell membrane (1-4). Cytochrome c oxidases are the most prevalent hemecopper oxidases. In this protein 4 electrons, provided by 4 cytochromes c, are used to reduce dioxygen to water. The 4 protons needed to make water are taken from the negative cytoplasmic side of the membrane, adding to the electrochemical gradient. Four additional protons are pumped across the membrane (5). Thus, each dioxygen molecule reduced by cytochrome c oxidase is coupled to the transfer of 8 charges across the membrane.The first step of electron transfer is from cytochrome c to Cu A , a dicopper center in subunit II which extends beyond the membrane on the proton release side of the protein (Figure 1). After receiving the electron, Cu A reduces the 6-coordinate, low-spin, bis-Hi...

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“…3). O P reduction to H P O at the binuclear heme a Q -Cu f center is considered by di¡erent groups to be directly coupled to proton pumping [4,12,22,23]. The crystallographic structures of Paracoccus denitri¢cans [23] and bovine heart cytochrome c oxidase [24] show a hydrogen-bond network of residues in subunits I and II which can provide an e¤cient electron transfer pathway from Cu e to heme a (see Fig.…”

Section: A Cooperative Proton Pump and Role Of Heme A In Cytochrome Cmentioning

confidence: 99%

“…For other details see text. step in the model of proton pumping denominated the`histidine cycle' [22,23,34].…”

Section: A Cooperative Proton Pump and Role Of Heme A In Cytochrome Cmentioning

confidence: 99%

A cooperative model for protonmotive heme‐copper oxidases. The role of heme a in the proton pump of cytochrome c oxidase

Papa¹,

Capitanio²,

Villani³

1998

FEBS Letters

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Oxido-reductions of metal centers in cytochrome c oxidase are linked to pK shifts of acidic groups in the enzyme (redox Bohr effects). The linkage at heme a results in proton uptake from the inner space upon reduction and proton release in the external space upon oxidation of the metal. The relationship of this process to the features of the proton pump in cytochrome c oxidase and its atomic structure revealed by X-ray crystallography to 2.8^2.3 A î resolution is examined. A mechanism for the proton pump of cytochrome c oxidase, based on cooperative coupling at heme a, is proposed.z 1998 Federation of European Biochemical Societies.

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Mechanism of proton translocation by the respiratory oxidases. The histidine cycle

Cited by 133 publications

References 25 publications

Fatty acids stimulate activity and restore respiratory control in a proton channel mutant of cytochrome c oxidase

Fatty acids stimulate activity and restore respiratory control in a proton channel mutant of cytochrome c oxidase

Calculated Proton Uptake on Anaerobic Reduction of CytochromecOxidase: Is the Reaction Electroneutral?

A cooperative model for protonmotive heme‐copper oxidases. The role of heme a in the proton pump of cytochrome c oxidase

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