Kinetics and thermodynamics of the P870+Q−A → P870+Q−B reaction in isolated reaction centers from the photosynthetic bacterium Rhodopseudomonas sphaeroides

Mancino, Lisa; Dean, David P.; Blankenship, Robert E.

doi:10.1016/0005-2728(84)90139-7

Cited by 86 publications

(73 citation statements)

References 18 publications

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“…k that depends on the light intensity of the measuring beam. This result was already obtained by Mancino et al (1984) in the only (to our best knowledge) previous paper discussing some aspects of the intensity of the measuring beam.…”

Section: Dabssupporting

confidence: 75%

“…Accordingly, the formal description of the actinic effects of the measuring light beam has been disregarded and only its influence on the observed rate of charge recombination from the secondary quinone was detailed by Mancino et al (1984) and Paddock et al (2006). In recent years, the investigation of RC light-induced conformational transitions has elicited experimental protocols involving non-negligible intensity measuring beams (Goushcha et al 2003) or the use of additional high intensity continuous light .…”

Section: Introductionmentioning

confidence: 99%

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Effects of the measuring light on the photochemistry of the bacterial photosynthetic reaction center from Rhodobacter sphaeroides

et al. 2011

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The bacterial reaction center (RC) has become a reference model in the study of the diverse interactions of quinones with electron transfer complexes. In these studies, the RC functionality was probed through flash-induced absorption changes where the state of the primary donor is probed by means of a continuous measuring beam and the electron transfer is triggered by a short intense light pulse. The single-beam set-up implies the use as reference of the transmittance measured before the light pulse. Implicit in the analysis of these data is the assumption that the measuring beam does not elicit the protein photochemistry. At variance, measuring beam is actinic in nature at almost all the suitable wavelengths. In this contribution, the analytical modelling of the time evolution of neutral and charge-separated RCs has been performed. The ability of measuring light to elicit RC photochemistry induces a first order growth of the charge-separated state up to a steady state that depends on the light intensity and on the occupation of the secondary quinone (Q(B)) site. Then the laser pulse pumps all the RCs in the charge-separated state. The following charge recombination is still affected by the measuring beam. Actually, the kinetics of charge recombination measured in RC preparation with the Q(B) site partially occupied are two-exponential. The rate constant of both fast and slow phases depends linearly on the intensity of the measuring beam while their relative weights depend not only on the fractions of RC with the Q(B) site occupied but also on the measuring light intensity itself.

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Section: Dabssupporting

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Effects of the measuring light on the photochemistry of the bacterial photosynthetic reaction center from Rhodobacter sphaeroides

et al. 2011

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“…In principle, the independence of k AB (1) on ⌬G ET 0 could be caused by the reaction being activationless (Ϫ⌬G ET 0 ϭ ). However, this is not the case for k AB (1) , for which a large activation energy is observed (9,19,29,30). Values for and ⌬G ET 0 have been determined to be Ϸ1.1 eV and ϷϪ0.1 eV, respectively (13,19,31,32).…”

Section: Discussionmentioning

confidence: 95%

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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“…More recent studies of proton uptake of the RC going along with Q A reduction that are based on delayed fluorescence measurements clearly demonstrated the pH dependence of the redox potential of Q A also in isolated RC (46). Reaction energies of the electron transfer from Q A to Q B estimated by the charge recombination rate in different labs vary from -52 to -78 meV (4,(47)(48)(49). Combining these values with the range of measured in situ redox potentials for E m (Q A ), we can conclude that the value of E m (Q B ) is in the range from 0 to +30 mV or -130 to -100 mV for the in situ redox potential E m (Q A ) of -50 and -180 mV, respectively.…”

Section: Methodsmentioning

confidence: 99%

Redox Potential of Quinones in Photosynthetic Reaction Centers fromRhodobacter sphaeroides: Dependence on Protonation of Glu-L212 and Asp-L213

2003

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The absolute values of the one-electron redox potentials of the two quinones (Q(A) and Q(B)) in bacterial photosynthetic reaction centers from Rhodobacter sphaeroides were calculated by evaluating the electrostatic energies from the solution of the linearized Poisson-Boltzmann equation at pH 7.0. The redox potential for Q(A) was calculated to be between -173 and -160 mV, which is close to the lowest measured values that are assumed to refer to nonequilibrated protonation patterns in the redox state Q(A)(-). The redox potential of quinone Q(B) is found to be about 160-220 mV larger for the light-exposed than for the dark-adapted structure. These values of the redox potentials are obtained if Asp-L213 is nearly protonated (probability 0.75-1.0) before and after electron transfer from Q(A) to Q(B), while Glu-L212 is partially protonated (probability 0.6) in the initial state Q(A)(-)Q(B)(0) and fully protonated in the final state Q(A)(0)Q(B)(-). Conversely, if the charge state of the quinones is varied from Q(A)(-)Q(B)(0) to Q(A)(0)Q(B)(-) corresponding to the electron transfer from Q(A) to Q(B), Asp-L213 remains protonated, while Glu-L212 changes its protonation state from 0.15 H(+) to fully protonated. In agreement with results from FTIR spectra, there is proton uptake at Glu-L212 going along with the electron transfer, whereas Asp-L213 does not change its protonation state. However, in our simulations Asp-L213 is considered to be protonated rather than ionized as deduced from FTIR spectra. The calculated redox potential of Q(A) shows little dependence on the charge state of Asp-L213, which is due to a strong coupling with the protonation state of Asp-M17 but increases by 50 mV if Glu-L212 changes from the ionized to the protonated charge state. Both are in agreement with fluorescence measurements observing the decay of SP(+)Q(A)(-) in a wide pH regime. The computed difference in redox potential of Q(B) in the light-exposed and dark-adapted structure was traced back to the hydrogen bond of Q(B) with His-L190 that is lost in the dark-adapted structure and the charge of the non-heme iron atom, which is closer to Q(B) in the light-exposed than in the dark-adapted structure.

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Kinetics and thermodynamics of the P870+Q−A → P870+Q−B reaction in isolated reaction centers from the photosynthetic bacterium Rhodopseudomonas sphaeroides

Cited by 86 publications

References 18 publications

Effects of the measuring light on the photochemistry of the bacterial photosynthetic reaction center from Rhodobacter sphaeroides

Effects of the measuring light on the photochemistry of the bacterial photosynthetic reaction center from Rhodobacter sphaeroides

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

Redox Potential of Quinones in Photosynthetic Reaction Centers fromRhodobacter sphaeroides: Dependence on Protonation of Glu-L212 and Asp-L213

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Kinetics and thermodynamics of the P870+Q−A → P870+Q−B reaction in isolated reaction centers from the photosynthetic bacterium Rhodopseudomonas sphaeroides

Cited by 86 publications

References 18 publications

Effects of the measuring light on the photochemistry of the bacterial photosynthetic reaction center from Rhodobacter sphaeroides

Effects of the measuring light on the photochemistry of the bacterial photosynthetic reaction center from Rhodobacter sphaeroides

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

Redox Potential of Quinones in Photosynthetic Reaction Centers fromRhodobacter sphaeroides: Dependence on Protonation of Glu-L212 and Asp-L213

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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