Electron Transfer in Natural Proteins Theory and Design

Moser, Christopher C.; Page, Christopher; Chen, Xiaoxi; Dutton, P. Leslie

doi:10.1007/0-306-46828-x_1

Cited by 21 publications

(20 citation statements)

References 75 publications

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“…This is in good agreement with the value that is commonly found for electron transfer in proteins (44,45), indicating that the pyranopterin cofactor confers no particularly effective electron transfer pathway between the molybdenum center and Fe/S I. Indeed, recent magnetic circular dichroism studies of xanthine oxidase have led to the proposal that electron transfer out of the molybdenum center is mediated by rather than interactions with the redox-active d xy orbital of the molybdenum center (46).…”

supporting

confidence: 73%

“…The high potential Fe/S II, however, intervenes between Fe/S I and the flavin. This situation is not an uncommon one in biological systems, and as has been pointed out by Dutton and co-workers (44,45), need not necessarily constitute a significant kinetic barrier to catalysis. It is important to recognize, however, how this arrangement influences the equilibrium distribution of reducing equivalents within the system, assuming (as is known to be the case for xanthine oxidase; Refs.…”

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confidence: 98%

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Coupled Electron/Proton Transfer in Complex Flavoproteins

Hille

Anderson

2001

Journal of Biological Chemistry

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A solvent kinetic isotope effect study of electron transfer in two complex flavoproteins, xanthine oxidase and trimethylamine dehydrogenase, has been undertaken. With xanthine oxidase, electron transfer from the molybdenum center to the proximal iron-sulfur center of the enzyme occurs with a modest solvent kinetic isotope effect of 2.2, indicating that electron transfer out of the molybdenum center is at least partially coupled to deprotonation of the Mo(V) donor. A Marcus-type analysis yields a decay factor, ␤, of 1.4 Å ؊1, indicating that, although the pyranopterin cofactor of the molybdenum center forms a nearly contiguous covalent bridge from the molybdenum atom to the proximal iron-sulfur center of the enzyme, it affords no exceptionally effective mode of electron transfer between the two centers. For trimethylamine dehydrogenase, rates of electron equilibration between the flavin and iron-sulfur center of the oneelectron reduced enzyme have been determined, complementing previous studies of electron transfer in the twoelectron reduced form. The results indicate a substantial solvent kinetic isotope effect of 10 ؎ 4, consistent with a model for electron transfer that involves discrete protonation/deprotonation and electron transfer steps. This contrasts to the behavior seen with xanthine oxidase, and the basis for this difference is discussed in the context of the structures for the two proteins and the ionization properties of their flavin sites. With xanthine oxidase, a rationale is presented as to why it is desirable in certain cases that the physical layout of redox-active sites not be uniformly increasing in reduction potential in the direction of physiological electron transfer.Electron transfer in biological systems is often linked either directly or indirectly to protonation/deprotonation events, and the overall process may involve either discrete or concerted electron and proton transfer (1, 2). Coupled electron/proton transfer may occur in systems consisting of either organic species (e.g. quinones and flavins) or metal centers (as a result of protonation of ligands to the metal upon reduction). These effects are manifested in the pH dependence of the reduction potential(s) and may also influence the kinetics of electron transfer (1, 2). The uptake of protons with reduction of a metal center is an example of the principle of charge neutrality in biological systems, in which the protein environment of a redox-active center is thought to stabilize a given overall charge for a redox-active center, regardless of the specific oxidation state of the center.We have previously examined electron transfer in complex redox-active enzymes using both pH jump and pulse radiolysis methodologies (3-9). Using the pH jump protocol, enzyme is placed in dilute buffer at a given pH and partially reduced by titration with a reagent such as sodium dithionite. The partially reduced enzyme is then mixed in a stopped-flow apparatus with more concentrated buffer at another pH, and the redistribution of reducing equivalents ...

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confidence: 73%

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confidence: 98%

Coupled Electron/Proton Transfer in Complex Flavoproteins

Hille

Anderson

2001

Journal of Biological Chemistry

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“…The first is an electronic term arising from the strength of the coupling of electron donor/acceptor wave functions that decreases exponentially upon increasing the distance between donor and acceptor. The second term depends on both the driving force (⌬G, proportional to the difference in redox midpoint potentials between donor and acceptor) and the reorgani- zation energy required to change the nuclear coordinates upon electron transfer (14,170,184,185,203).…”

Section: Principles Of Electron Transfer Between Cofactors In Promentioning

confidence: 99%

Electronic Connection Between the Quinone and CytochromecRedox Pools and Its Role in Regulation of Mitochondrial Electron Transport and Redox Signaling

Sarewicz

Osyczka

2015

Physiological Reviews

140

141

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Physiol Rev 95: 219 -243, 2015; doi:10.1152/physrev.00006.2014.-Mitochondrial respiration, an important bioenergetic process, relies on operation of four membranous enzymatic complexes linked functionally by mobile, freely diffusible elements: quinone molecules in the membrane and water-soluble cytochromes c in the intermembrane space. One of the mitochondrial complexes, complex III (cytochrome bc 1 or ubiquinol: cytochrome c oxidoreductase), provides an electronic connection between these two diffusible redox pools linking in a fully reversible manner two-electron quinone oxidation/reduction with one-electron cytochrome c reduction/oxidation. Several features of this homodimeric enzyme implicate that in addition to its well-defined function of contributing to generation of proton-motive force, cytochrome bc 1 may be a physiologically important point of regulation of electron flow acting as a sensor of the redox state of mitochondria that actively responds to changes in bioenergetic conditions. These features include the following: the opposing redox reactions at quinone catalytic sites located on the opposite sides of the membrane, the inter-monomer electronic connection that functionally links four quinone binding sites of a dimer into an H-shaped electron transfer system, as well as the potential to generate superoxide and release it to the intermembrane space where it can be engaged in redox signaling pathways. Here we highlight recent advances in understanding how cytochrome bc 1 may accomplish this regulatory physiological function, what is known and remains unknown about catalytic and side reactions within the quinone binding sites and electron transfers through the cofactor chains connecting those sites with the substrate redox pools. We also discuss the developed molecular mechanisms in the context of physiology of mitochondria.

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“…The equations allow us to isolate the relevant ratios of rate constants that control the yield and the lifetime. These conditions are used to set bounds on the physical distances and potentials that makeup the PCT using a standard semiclassical model which incorporates Marcus theory for the dependence and an exponential drop-off of the ET rate with distance [28] as parameterized in the Moser-Dutton ruler [29] , [30] . We report two major findings: first, that the highest yield occurs when the primary-donor cofactor is closest to the acceptor cofactor and second, that the highest yield and efficiency occurs when the absorption frequency of the primary-donor is more than twice the reorganization energy of the first electron transfer.…”

Section: Introductionmentioning

confidence: 99%

Fundamental Limits on Wavelength, Efficiency and Yield of the Charge Separation Triad

et al. 2012

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In an attempt to optimize a high yield, high efficiency artificial photosynthetic protein we have discovered unique energy and spatial architecture limits which apply to all light-activated photosynthetic systems. We have generated an analytical solution for the time behavior of the core three cofactor charge separation element in photosynthesis, the photosynthetic cofactor triad, and explored the functional consequences of its makeup including its architecture, the reduction potentials of its components, and the absorption energy of the light absorbing primary-donor cofactor. Our primary findings are two: First, that a high efficiency, high yield triad will have an absorption frequency more than twice the reorganization energy of the first electron transfer, and second, that the relative distance of the acceptor and the donor from the primary-donor plays an important role in determining the yields, with the highest efficiency, highest yield architecture having the light absorbing cofactor closest to the acceptor. Surprisingly, despite the increased complexity found in natural solar energy conversion proteins, we find that the construction of this central triad in natural systems matches these predictions. Our analysis thus not only suggests explanations for some aspects of the makeup of natural photosynthetic systems, it also provides specific design criteria necessary to create high efficiency, high yield artificial protein-based triads.

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Electron Transfer in Natural Proteins Theory and Design

Cited by 21 publications

References 75 publications

Coupled Electron/Proton Transfer in Complex Flavoproteins

Coupled Electron/Proton Transfer in Complex Flavoproteins

Electronic Connection Between the Quinone and CytochromecRedox Pools and Its Role in Regulation of Mitochondrial Electron Transport and Redox Signaling

Fundamental Limits on Wavelength, Efficiency and Yield of the Charge Separation Triad

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