Ligand binding reveals protonation events at the active site of cytochrome c oxidase; is the K-pathway used for the transfer of H+ or OH−?

Sigurdson, Håkan; Brändén, Magnus; Namslauer, Andreas; Brzezinski, Peter

doi:10.1016/s0162-0134(01)00348-8

Cited by 10 publications

(12 citation statements)

References 29 publications

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“…At high pH (>7.5), the rapid electron transfer between the hemes is followed by an absorbance change and a net proton release to the bulk solution on a millisecond time scale (termed the “millisecond phase”) ( − ).…”

Section: Resultsmentioning

confidence: 99%

“…At high pH (>7.5), the 3 μs electron transfer from heme a 3 to heme a is followed by proton release to the bulk solution through the K-pathway. Several different possible proton donors were suggested for release of the proton, where one likely candidate is a water molecule that releases a proton, followed by hydroxide binding to the oxidized heme a 3 ( , ). On the basis of the pH dependence of the rate and extent of the reaction, a p K a of ∼9 ( , ) was estimated for the protonatable group from which the proton is released.…”

Section: Discussionmentioning

confidence: 99%

“…Several different possible proton donors were suggested for release of the proton, where one likely candidate is a water molecule that releases a proton, followed by hydroxide binding to the oxidized heme a 3 ( , ). On the basis of the pH dependence of the rate and extent of the reaction, a p K a of ∼9 ( , ) was estimated for the protonatable group from which the proton is released. In the previous studies using the bovine heart enzyme, the spectral changes associated with the millisecond phase were interpreted in terms of electron transfer from heme a 3 to heme a .…”

Section: Discussionmentioning

confidence: 99%

“…The kinetics of proton uptake and release in the absence of O 2 , coupled to internal electron transfer within the enzyme, can be investigated directly after flash photolysis of CO from the mixed-valence state (two-electron-reduced enzyme). In this state, heme a and Cu A are oxidized and heme a 3 and Cu B are reduced with CO bound to heme a 3 ( − ). The CO ligand stabilizes the reduced state of the binuclear center.…”

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confidence: 99%

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Water−Hydroxide Exchange Reactions at the Catalytic Site of Heme−Copper Oxidases

et al. 2003

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Membrane-bound heme-copper oxidases catalyze the reduction of O(2) to water. Part of the free energy associated with this process is used to pump protons across the membrane. The O(2) reduction reaction results in formation of high-pK(a) protonatable groups at the catalytic site. The free energy associated with protonation of these groups is used for proton pumping. One of these protonatable groups is OH(-), coordinated to the heme and Cu(B) at the catalytic site. Here we present results from EPR experiments on the Rhodobacter sphaeroides cytochrome c oxidase, which show that at high pH (9) approximately 50% of oxidized heme a(3) is hydroxide-ligated, while at low pH (6.5), no hydroxide is bound to heme a(3). The kinetics of hydroxide binding to heme a(3) were investigated after dissociation of CO from heme a(3) in the enzyme in which the heme a(3)-Cu(B) center was reduced while the remaining redox sites were oxidized. The dissociation of CO results in a decrease of the midpoint potential of heme a(3), which results in electron transfer (tau approximately equal 3 micros) from heme a(3) to heme a in approximately 100% of the enzyme population. At pH >7.5, the electron transfer is followed by proton release from a H(2)O molecule to the bulk solution (tau approximately equal 2 ms at pH 9). This reaction is also associated with absorbance changes of heme a(3), which on the basis of the results from the EPR experiments are attributed to formation of hydroxide-ligated heme a(3). The OH(-) bound to heme a(3) under equilibrium conditions at high pH is also formed transiently after O(2) reduction at low pH. It is proposed that the free energy associated with electron transfer to the binuclear center and protonation of this OH(-) upon reduction of the recently oxidized enzyme provides the driving force for the pumping of one proton.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Water−Hydroxide Exchange Reactions at the Catalytic Site of Heme−Copper Oxidases

et al. 2003

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“…A channel for hydroxide ions is difficult to distinguish empirically from one for protons. It has been argued that a pH dependency of the high pH component of CO recombination to mixed valence CcO supports its being a proton channel [69]. However, this pH dependency is rather weaker than should be expected and so does not provide a definitive resolution.…”

Section: The K Channelmentioning

confidence: 98%

Functions of the hydrophilic channels in protonmotive cytochrome c oxidase

Rich

Maréchal

2013

J. R. Soc. Interface.

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The structures and functions of hydrophilic channels in electron-transferring membrane proteins are discussed. A distinction is made between proton channels that can conduct protons and dielectric channels that are nonconducting but can dielectrically polarize in response to the introduction of charge changes in buried functional centres. Functions of the K, D and H channels found in A1-type cytochrome c oxidases are reviewed in relation to these ideas. Possible control of function by dielectric channels and their evolutionary relation to proton channels is explored.

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Et tu, Grotthuss! and other unfinished stories

Cukierman

2006

Biochimica et Biophysica Acta (BBA) - Bioenergetics

561

452

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This review article is divided into three sections. In Section 1, a short biographical note on Freiherr von Grotthuss is followed by a detailed summary of the main findings and ideas present in his 1806 paper. Attempts to place Grotthuss contribution in the context of the science done at his time were also made. In Section 2, the modern version of the Grotthuss mechanism is reviewed. The classical Grotthuss model has been recently questioned and new mechanisms and ideas regarding proton transfer are briefly discussed. The last section discusses the significance of a classical Grotthuss mechanism for proton transfer in water chains inside protein cavities. This has been an interesting new twist in the ongoing history of the Grotthuss mechanism. A summary and discussion of what was learned from probably the simplest currently available experimental models of proton transfer in water wires in semi-synthetic ion channels are critically presented. This review ends discussing some of the questions that need to be addressed in the near future.

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Ligand binding reveals protonation events at the active site of cytochrome c oxidase; is the K-pathway used for the transfer of H+ or OH−?

Cited by 10 publications

References 29 publications

Water−Hydroxide Exchange Reactions at the Catalytic Site of Heme−Copper Oxidases

Water−Hydroxide Exchange Reactions at the Catalytic Site of Heme−Copper Oxidases

Functions of the hydrophilic channels in protonmotive cytochrome c oxidase

Et tu, Grotthuss! and other unfinished stories

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