Investigations on the influence of headgroup substitution and isoprene side-chain length in the function of primary and secondary quinones of bacterial reaction centers

McComb, James Craig; Stein, R.R.; Wraight, Colin A.

doi:10.1016/0005-2728(90)90227-u

Cited by 94 publications

(105 citation statements)

References 29 publications

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“…Analogous effects of strong entropyenthalpy compensation have been recently reported for the binding of ubiquinones of different tail length at the QA site of Rb. spharroidrs [37]. The suggestion that the counterbalance of enthalpic and entropic contributions is due to an antagonistic interaction between the headgroup and the side chain seems quite reasonable also in relation to our data.…”

Section: H ) P+ Qi Recombination In Menaquinone-reconstituted Reactiosupporting

confidence: 88%

“…The charge recombination between P' and Q< appears therefore to occur directly without involving a thermally activated intermediate state. The alternative possibility of an apparent temperature independence due to an opposing temperature dependence of QB binding and of the PfQA/PtQe equilibrium, discussed by McComb et al [37], seems unlikely here due to the large temperature range examined. When measurements were performed at temperatures higher than 50°C the decay of P + was progressively accelerated; the apparent rate constant for PtQ" charge recombination increased by approximately one order-of-magnitude over a 10 "C interval, reaching a value of 2 sC1 at 60°C (Fig.…”

Section: U ) Reaction Centers Reconstituted With Uhiquinonementioning

confidence: 70%

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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

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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...

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Section: H ) P+ Qi Recombination In Menaquinone-reconstituted Reactiosupporting

confidence: 88%

Section: U ) Reaction Centers Reconstituted With Uhiquinonementioning

confidence: 70%

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

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“…The result reported in this work and by McComb et al (44), that the rates of k AB (1) for RCs with Q 10 , Q 2 , or Q 0 in the Q B site are the same, excludes interactions associated with the isoprenoid tail as rate limiting. However, interactions of the quinone head group, for example, -stacking with Phe-L216 or hydrogen-bonding between the O-4 carbonyl of Q B and the amide hydrogen of Ile-L224, may limit the rate of movement between the D and P states.…”

Section: Discussionsupporting

confidence: 67%

Conformational gating of the electron transfer reaction Q _A ⁻ ^⋅ Q _B → Q _A Q _B ⁻ ^⋅ in bacterial reaction centers of Rhodobacter sphaeroides determined by a driving force assay

Graige

Fehér

Okamura

1998

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

211

235

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The mechanism of the electron transfer reaction, Q A ؊ ⅐ Q B 3 Q A Q B ؊ ⅐ , was studied in isolated reaction centers from the photosynthetic bacterium Rhodobacter sphaeroides by replacing the native Q 10 in the Q A binding site with quinones having different redox potentials. These substitutions are expected to change the intrinsic electron transfer rate by changing the redox free energy (i.e., driving force) for electron transfer without affecting other events that may be associated with the electron transfer (e.g., protein dynamics or protonation). The electron transfer from Q A ؊ ⅐ to Q B was measured by three independent methods: a functional assay involving cytochrome c 2 to measure the rate of Q A ؊ ⅐ oxidation, optical kinetic spectroscopy to measure changes in semiquinone absorption, and kinetic near-IR spectroscopy to measure electrochromic shifts that occur in response to electron transfer. The results show that the rate of the observed electron transfer from Q A ؊ ⅐ to Q B does not change as the redox free energy for electron transfer is varied over a range of 150 meV. The strong temperature dependence of the observed rate rules out the possibility that the reaction is activationless. We conclude, therefore, that the independence of the observed rate on the driving force for electron transfer is due to conformational gating, that is, the rate limiting step is a conformational change required before electron transfer. This change is proposed to be the movement, controlled kinetically either by protein dynamics or intermolecular interactions, of Q B by Ϸ5 Å as observed in the x-ray studies of Stowell et al.

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“…However, this is unlikely given the independence of the rate on the length of the isoprenoid chain of Q B (9,41,42) and the observation of the same rate constant k AB (1) measured in a mutant RC in which Q B was predominantly structurally located in the proximal site (29). Another possible gating mechanism involves a conformational change in the protein that is required to favor the Q A −• Q B → Q A Q B −• reaction.…”

mentioning

confidence: 99%

Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

et al. 2006

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The reaction center (RC) from Rhodobacter sphaeroides captures light energy by electron transfer between quinones Q A and Q B , involving a conformational gating step. In this work, conformational states of D +• Q B −• were trapped (80K) and studied using EPR spectroscopy in mutant RCs that lack Q A in which Q B was reduced by the bacteriopheophytin along the B-branch. In mutant RCs frozen in the dark, a light induced EPR signal due to D +• Q B −• formed in 30% of the sample with low quantum yield (0.2%-20%) and decayed in 6 s. A small signal with similar characteristics was also observed in native RCs. In contrast, the EPR signal due to D + Q B − in mutant RCs illuminated while freezing formed in ~ 95% of the sample that did not decay (τ >10 7 s) at 80K. In all samples, the observed gvalues were the same (g=2.0026) indicating that all active Q B −• was located in a proximal conformation coupled with the non-heme Fe 2+ . We propose that before electron transfer at 80K, the majority (~70%) of Q B , structurally located in the distal site, cannot be stably reduced, while the minor ( can be considered to be the initial and final states along the reaction coordinate for conformationallygated electron transfer.

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Investigations on the influence of headgroup substitution and isoprene side-chain length in the function of primary and secondary quinones of bacterial reaction centers

Cited by 94 publications

References 29 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

Conformational gating of the electron transfer reaction Q _A ⁻ ^⋅ Q _B → Q _A Q _B ⁻ ^⋅ in bacterial reaction centers of Rhodobacter sphaeroides determined by a driving force assay

Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

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Investigations on the influence of headgroup substitution and isoprene side-chain length in the function of primary and secondary quinones of bacterial reaction centers

Cited by 94 publications

References 29 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

Conformational gating of the electron transfer reaction Q A − ⋅ Q B → Q A Q B − ⋅ in bacterial reaction centers of Rhodobacter sphaeroides determined by a driving force assay

Trapped Conformational States of Semiquinone (D+•QB-•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers

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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

Conformational gating of the electron transfer reaction Q _A ⁻ ^⋅ Q _B → Q _A Q _B ⁻ ^⋅ in bacterial reaction centers of Rhodobacter sphaeroides determined by a driving force assay

Trapped Conformational States of Semiquinone (D⁺^•Q_B^-^•) Formed by B-Branch Electron Transfer at Low Temperature in Rhodobacter sphaeroides Reaction Centers