Electrochemistry of ubiquinones

Prince, Roger C.; Dutton, P. Leslie; Bruce, J. Malcolm

doi:10.1016/0014-5793(83)80981-8

Cited by 176 publications

(110 citation statements)

References 6 publications

Supporting

Mentioning

103

Contrasting

Order By: Relevance

“…In order that, at 35"C, the contribution of the indirect recombination pathway to the rate constant does not exceed lo%, AG must be > 180 meV. This value seems reasonable when compared to the much smaller P'QLQB-P'QAQi energy gap evaluated in vivo [30] and in menaquinone-reconstituted RCs (see below) and is consistent with the more positive redox midpoint potential of UQ-3 as compared to menaquinone [48].…”

Section: A ) P+ Q I Recombination In Uq-reconstituted Reaction Centersmentioning

confidence: 61%

Temperature dependence of charge recombination from the P⁺Q_A⁻ and P⁺Q_B⁻ states in photosynthetic reaction centers isolated from the thermophilic bacterium Chloroflexus aurantiacus

Venturoli

Trotta²,

Feick

et al. 1991

European Journal of Biochemistry

View full text Add to dashboard Cite

The temperature dependence of charge recombination from the P'QA and from the P'QS states produced by a flash was studied in reaction centers isolated from the photosynthetic thermophilic bacterium Chlorojlexus aurantiacus. P designates the primary electron donor; QA and Qe the primary and secondary quinone electron acceptors respectively. In QB-depleted reaction centers the rate constant (kAp) for P'QA recombination was temperature independent between 0-50°C (17.6 & 0.7 s -l at pH 8 and pH 10). The same value was obtained in intact membranes in the presence of o-phenanthroline. Upon lowering the temperature from 250 K to 160 K, kAP increased by a factor of two and remained constant down to 80 K. The overall temperature dependence of kAP was consistent with an activationless process. Ubiquinone (UQ-3) and different types of menaquinone were used for QB reconstitution. In UQ-3-reconstituted reaction centers charge recombination was monoexponential (rate constant k = 0.18 0.03 s-') and temperature independent between 5-40°C. In contrast, in menaquinone-3-and menaquinone-4-reconstituted reaction centers P + rereduction following a flash was markedly biphasic and temperature dependent. In menaquinone-6-reconstituted reaction centers a minor contribution from a third kinetic phase corresponding to P'QA charge recombination was detected. Analysis of these kinetics and of the effects of the inhibitor o-phenanthroline at high temperature suggest that in detergent suspensions of menaquinone-reconstituted reaction centers a redox reaction removing electrons from the quinone acceptor complex competes with charge recombination. Instability of the semiquinone anions is more pronounced when QB is a short-chain menaquinone. From the temperature dependence of P + decay the activation parameters for the P' Q; recombination and for the competing side oxidation of the reduced menaquinone acceptor have been derived. For both reactions the activation enthalpies and entropies change markedly with menaquinone chain length but counterbalance each other, resulting in activation free energies at ambient temperature independent of the menaquinone tail. When reaction centers are incorporated into phospholipid vesicles containing menaquinone-8 a temperature-dependent, monophasic, o-phenanthroline-sensitive recombination from the P'Q; state is observed, which is consistent with the formation of stable semiquinone anions. This result seems to indicate a proper QB functioning in the two-subunit reaction center isolated from Chlorojlexus aurantiucus when the complex is inserted into a lipid bilayer.Reaction centers of photosynthetic organisms are membrane-bound pigment-protein complexes that convert the photon energy absorbed by the antenna system into electrochemical energy. In two species of purple photosynthetic bacteria (Rhodopseudomonas viridis and Rhodobacter sphaeroides) the three-dimensional structure of the reaction center (RC) has been determined to atomic resolution by X-ray diffraction. The RC is composed of two membrane-spanning po...

show abstract

Section: A ) P+ Q I Recombination In Uq-reconstituted Reaction Centersmentioning

confidence: 61%

Temperature dependence of charge recombination from the P⁺Q_A⁻ and P⁺Q_B⁻ states in photosynthetic reaction centers isolated from the thermophilic bacterium Chloroflexus aurantiacus

Venturoli

Trotta²,

Feick

et al. 1991

European Journal of Biochemistry

View full text Add to dashboard Cite

show abstract

“…sphaeroides (8). Methoxy-substituted quinones are notorious for the dependence of their electron affinity on the dihedral angle defining the position of the OOCH 3 bond relative to the quinone ring plane, and it has long been proposed that the protein at the binding sites can tune the redox potential of ubiquinones by modulating the conformation of the methoxy groups (36,37). The vibrational IR frequency of the carbonyls and the redox properties of ubiquinones in solution as a function of the conformation of the methoxy groups (in-plane or out-of-plane orientation of the OOCH 3 bond with respect to the quinone ring) have been recently investigated in detail (38).…”

Section: Discussionmentioning

confidence: 99%

Efficient exchange of the primary quinone acceptor Q _A in isolated reaction centers of Rhodopseudomonas viridis

Breton

1997

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

View full text Add to dashboard Cite

USA 88, 3491-3495], who were able to extract with detergents the firmly bound ubiquinone Q A from the RC of Rhodobacter sphaeroides and reconstitute the site with extraneous quinones. Up to now a comparable protocol was lacking for the RC of Rhodopseudomonas viridis despite the fact that its Q A site, which contains 2-methyl-3-nonaprenyl-1,4-naphthoquinone (menaquinone-9), has provided the best x-ray structure available. Fourier transform infrared difference spectroscopy, together with the use of isotopically labeled quinones, can probe the interaction of Q A with the RC protein. We establish that a simple incubation procedure of isolated RCs of Rp. viridis with an excess of extraneous quinone allows the menaquinone-9 in the Q A site to be almost quantitatively replaced either by vitamin K 1 , a close analogue of menaquinone-9, or by ubiquinone. To our knowledge, this is the first report of quinone exchange in bacterial photosynthesis. The Fourier transform infrared data on the quinone and semiquinone vibrations show a close similarity in the bonding interactions of vitamin K 1 with the protein at the Q A site of Rp. viridis and Rb. sphaeroides, whereas for ubiquinone these interactions are significantly different. The results are interpreted in terms of slightly inequivalent quinone-protein interactions by comparison with the crystallographic data available for the Q A site of the two RCs.In the reaction center (RC) of photosynthetic purple bacteria, two quinone molecules (Q A and Q B ) play an essential role in coupling the electron-and proton-transfer reactions leading to the conversion of light energy into chemical energy (for a review, see ref. 1). Following absorption of a photon, transmembrane electron transfer occurs between a dimer of bacteriochlorophyll molecules and Q A in Ϸ200 ps and then to Q B in 20-100 s. Q A acts as a one-electron acceptor only, whereas Q B plays the role of a two-electron gate and can accept two protons before leaving the RC.The crystal structure of the RCs of the two species of photosynthetic bacteria that have been investigated the most, namely Rhodobacter sphaeroides and Rhodopseudomonas viridis, has been solved in several laboratories (2-9). The best atomic resolution for which structural data on the Q A binding sites are presently available is 2.65 Å for the former species and 2.3 Å for the latter. For these two highly homologous proteins, the structural models reveal that the bonding interactions of Q A , which are 2-methyl-3-nonaprenyl-1,4-naphthoquinone (menaquinone-9) in Rp. viridis and 2,3-dimethoxy-5-methyl-6-decaprenyl-1,4-benzoquinone (ubiquinone-10) in Rb. sphaeroides, are relatively well defined (within the Ϯ0.25-to 0.5-Å precision on the position of the nonhydrogen atoms in the x-ray data), although the details vary among the various structures. Notably, the identity of some of the residues involved in hydrogen bonding and the relative strength of the hydrogen bonds to the two carbonyls of Q A are still not totally clear (2-9).The precise knowledge of the interac...

show abstract

“…In vitro electrochemical measurements indicate that a methoxy group attached to the quinone ring can lower the reduction potential through delocalization of the lone pair electrons from the methoxy oxygen to the system of the ring, and the effect is largest for a methoxy group in a conformation coplanar to the ring (12). Based on molecular orbital calculations, the influence of the methoxy torsional angle on the reduction potentials of the UQ can be as significant as 0.4 eV, and it has been proposed that electron transfer reactions can be controlled allosterically through specific orientations of the methoxy groups of the UQ imposed by * This work was supported, in whole or in part, by National Institutes of Health the protein environments (10).…”

mentioning

confidence: 99%

Exploring by Pulsed EPR the Electronic Structure of Ubisemiquinone Bound at the QH Site of Cytochrome bo3 from Escherichia coli with in Vivo 13C-Labeled Methyl and Methoxy Substituents

Lin

Shubin

Samoilova

et al. 2011

Journal of Biological Chemistry

View full text Add to dashboard Cite

The cytochrome bo 3 ubiquinol oxidase from Escherichia coli resides in the bacterial cytoplasmic membrane and catalyzes the two-electron oxidation of ubiquinol-8 and four-electron reduction of O 2 to water. The one-electron reduced semiquinone forms transiently during the reaction, and the enzyme has been demonstrated to stabilize the semiquinone. The semiquinone is also formed in the D75E mutant, where the mutation has little influence on the catalytic activity, and in the D75H mutant, which is virtually inactive. In this work, wild-type cytochrome bo 3 as well as the D75E and D75H mutant proteins were prepared with ubiquinone-8 13 C-labeled selectively at the methyl and two methoxy groups. This was accomplished by expressing the proteins in a methionine auxotroph in the presence of L-methionine with the side chain methyl group 13 C-labeled. The 13 Clabeled quinone isolated from cytochrome bo 3 was also used for the generation of model anion radicals in alcohol. Two-dimensional pulsed EPR and ENDOR were used for the study of the 13 C methyl and methoxy hyperfine couplings in the semiquinone generated in the three proteins indicated above and in the model system. The data were used to characterize the transferred unpaired spin densities on the methyl and methoxy substituents and the conformations of the methoxy groups. In the wild type and D75E mutant, the constraints on the configurations of the methoxy side chains are similar, but the D75H mutant appears to have altered methoxy configurations, which could be related to the perturbed electron distribution in the semiquinone and the loss of enzymatic activity. Ubiquinone (UQ)3 functions as a membrane-soluble twoelectron carrier. It is often found as a cofactor in many respiratory and photosynthetic complexes and plays an important role in biological oxidation-reduction reactions. Many of these reactions consist of one-electron transfer steps and involve the one-electron reduced ubisemiquinone species as the intermediates. Knowledge of how the semiquinone (SQ) radicals are stabilized in these complexes is critical to understand their reaction mechanisms. The quinone binding sites located in the respiratory and photosynthetic enzymes are significantly different (1), and each protein fine tunes the properties of the bound quinone cofactor by providing a unique environment in order to accomplish its own electron transfer process (2). The well characterized quinone binding sites include those from bacterial photosynthetic reaction centers (3), cytochrome bo 3 ubiquinol oxidase (cyt bo 3 ) from Escherichia coli (4), cytochrome bc 1 complexes (5), photosystems I and II, and some others (6 -9).A SQ can bind within a protein site in a manner that favors either the neutral (QH ⅐ ) or anionic (Q . ) form or intermediate states with partial charge remaining on the SQ. The proton locations along the hydrogen bonds to the quinone carbonyls determine the net charge on the SQ. The formation of hydrogen bonds of different strengths to the quinone oxygens usually leads to an asym...

show abstract

Electrochemistry of ubiquinones

Cited by 176 publications

References 6 publications

Temperature dependence of charge recombination from the P⁺Q_A⁻ and P⁺Q_B⁻ states in photosynthetic reaction centers isolated from the thermophilic bacterium Chloroflexus aurantiacus

Temperature dependence of charge recombination from the P⁺Q_A⁻ and P⁺Q_B⁻ states in photosynthetic reaction centers isolated from the thermophilic bacterium Chloroflexus aurantiacus

Efficient exchange of the primary quinone acceptor Q _A in isolated reaction centers of Rhodopseudomonas viridis

Exploring by Pulsed EPR the Electronic Structure of Ubisemiquinone Bound at the QH Site of Cytochrome bo3 from Escherichia coli with in Vivo 13C-Labeled Methyl and Methoxy Substituents

Contact Info

Product

Resources

About

Electrochemistry of ubiquinones

Cited by 176 publications

References 6 publications

Temperature dependence of charge recombination from the P+QA− and P+QB− states in photosynthetic reaction centers isolated from the thermophilic bacterium Chloroflexus aurantiacus

Temperature dependence of charge recombination from the P+QA− and P+QB− states in photosynthetic reaction centers isolated from the thermophilic bacterium Chloroflexus aurantiacus

Efficient exchange of the primary quinone acceptor Q A in isolated reaction centers of Rhodopseudomonas viridis

Exploring by Pulsed EPR the Electronic Structure of Ubisemiquinone Bound at the QH Site of Cytochrome bo3 from Escherichia coli with in Vivo 13C-Labeled Methyl and Methoxy Substituents

Contact Info

Product

Resources

About

Temperature dependence of charge recombination from the P⁺Q_A⁻ and P⁺Q_B⁻ states in photosynthetic reaction centers isolated from the thermophilic bacterium Chloroflexus aurantiacus

Temperature dependence of charge recombination from the P⁺Q_A⁻ and P⁺Q_B⁻ states in photosynthetic reaction centers isolated from the thermophilic bacterium Chloroflexus aurantiacus

Efficient exchange of the primary quinone acceptor Q _A in isolated reaction centers of Rhodopseudomonas viridis