Charge recombination from the P+Q−A state in reaction centers from Rhodopseudomonas viridis

Shopes, Robert J.; Wraight, Colin A.

doi:10.1016/0005-2728(87)90093-4

Cited by 92 publications

(87 citation statements)

References 40 publications

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“…[12]), which is not modified by replacement of L162Y. The rate of the S phase, which has been attributed to 3 P in WT RC [3], is also nearly the same and it shows a similar temperature dependence.…”

Section: Effect Of Temperature On the Kinetics Of Cytochrome Oxidationmentioning

confidence: 50%

“…Absorption spectra of RC of the L162T mutant recorded at 8 K before and after a short illumination show that heme c-559 of the cytochrome is partly and irreversibly photooxidized (data not shown). At this temperature, the cytochrome does not work in about 60% of RC and P + decays presumably by back-reaction with Q^, a reaction which has a i 1/2 of a few ms at low temperature [12]. These centers function identically at the first and subsequent flashes (Figs.…”

Section: Effect Of Temperature On the Extent Of Cytochrome Oxidationmentioning

confidence: 97%

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Very fast electron transfer from cytochrome to the bacterial photosynthetic reaction center at low temperature

et al. 1997

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Electron transfer from the proximal heme c-559 to the primary donor P has been studied in reaction centers of the photosynthetic bacterium Rhodopseudomonas viridis in which the tyrosine residue L162 was replaced by threonine. In the wild type, when the two high-potential hemes of the tetraheme cytochrome are reduced before flash excitation, a rapid electron transfer (t V2 = 190 ns) observed at ambient temperature disappears below 190 K. In the mutant, the reaction is partly maintained down to 8 K, leading to irreversible charge separation. The reaction rate is nearly temperature-independent between 294 K and 8 K (t\a ~ 450 ns). The different behavior of wild type and mutant reaction centers is attributed to differences in a network of water molecules, the freezing of which may block structural reorganizations associated with cytochrome oxidation, in the wild type but not in the mutant.

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Section: Effect Of Temperature On the Kinetics Of Cytochrome Oxidationmentioning

confidence: 50%

Section: Effect Of Temperature On the Extent Of Cytochrome Oxidationmentioning

confidence: 97%

Very fast electron transfer from cytochrome to the bacterial photosynthetic reaction center at low temperature

et al. 1997

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“…Both processes are somewhat biphasic, although the difference in rates is larger for the electron transfer from Q B -to P + than from Q A - (14,(54)(55)(56). In RCs frozen in the light in the absence of Q B , Q A -to P + electron transfer is better analyzed by a distribution of exponentials than by one or two exponentials (12,13).…”

Section: The Charge Recombination Rate In the Light Conformation Is Cmentioning

confidence: 98%

Trapping Conformational Intermediate States in the Reaction Center Protein from Photosynthetic Bacteria

Gunner

2001

Biochemistry

108

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In protein, conformational changes are often crucial for function but not easy to observe. Two functionally relevant conformational intermediate states of photosynthetic reaction center protein (RCs) are trapped and characterized at low temperature. RCs frozen in the dark do not allow electron transfer from the reduced primary quinone, Q A -, to the secondary quinone, Q B . In contrast, RCs frozen under illumination in the product (P + Q A Q B -) state, with the oxidized electron donor, P + , and reduced Q B -, return to the ground state at cryogenic temperature in a conformation that allows a high yield of Q B reduction. Thus, RCs frozen under illumination are found to be trapped above the ground state in a conformation that allows product formation. When the temperature is raised above 120 K, the protein relaxes to an inactive conformation which is different from the RCs frozen in the dark. The activation energy for this change is 87 ( 8 meV, and the active and inactive states differ in energy by only 16 ( 3 meV. Thus, there are several conformational substates along the reaction coordinate with different transition temperatures. The ground state spectra of the RCs in active and inactive conformations report differences in the intraprotein electrostatic field, demonstrating that the dipole or charge distribution has changed. In addition, the electrochromic shift associated with the Q A -to Q B electron transfer at low temperature was characterized. The electron-transfer rate from Q B -to P + was measured at cryogenic temperature and is similar to the rate at room temperature, as expected for an exothermic, electron tunneling reaction in RCs.Conformational flexibility is important for the function of proteins (1, 2). At room temperature, proteins fluctuate among many conformational states. At low temperature, proteins will become trapped in harmonic motions near the conformation it was frozen into (3-9). Intraprotein reactions are inhibited if this conformation cannot access the transition state. When the temperature is raised, relaxation between conformational substates becomes possible. Elastic incoherent neutron scattering and X-ray crystallography measurements of bacteriorhodopsin (10) and myoglobin (4) show that different parts of the protein relax at different temperatures (11).Bacterial photosynthetic reaction center protein (RCs) 1 has a number of physiological electron tunneling reactions that occur even at cryogenic temperatures. This system can therefore be used to characterize conformational substates of physiologically important reactions. Previous studies of RCs have characterized the protein at cryogenic temperatures. RCs can be trapped in a distribution of substates which exhibit a wider distribution of reaction rates (12,13). Other studies have characterized unrelaxed product states (14). In addition, reactions that normally do not occur at low temperatures have been observed when the protein is frozen into appropriate conformational states (12).The bacterial photosynthetic reaction c...

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“…k T is the limit value of the rate constant of P + Q A -recombination reached at low temperature. It has previously been measured for anthraquinone as 10 s -1 (40).…”

Section: Bacterial Strains and Growthmentioning

confidence: 99%

Evidence for Delocalized Anticooperative Flash Induced Proton Binding as Revealed by Mutants at the M266His Iron Ligand in Bacterial Reaction Centers

et al. 2007

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Bacterial reaction centers (RCs) convert light energy into chemical free energy Via the double reduction and protonation of the secondary quinone electron acceptor, Q B , to the dihydroquinone Q B H 2 . Two RC mutants (M266His f Leu and M266His f Ala) with a modified ligand of the non-heme iron have been studied by flash-induced absorbance change spectroscopy. No important changes were observed for the rate constants of the first and second electron transfers between the first quinone electron acceptor, Q A , and Q B . However, in the M266HL mutant a destabilization of ∼40 meV of the free energy level of Q A -was observed, at variance with the M266HA mutant. The superposition of the three-dimensional X-ray structures of the three proteins in the Q A region provides no obvious explanation for the energy modification in the M266HL mutant. The shift of the midpoint redox potential of Q A /Q A -in M266HL caused accelerated recombination of the charges in the P + Q A -state of the RCs where the native Q A was replaced by a low potential anthraquinone (AQ A ). As previously reported for the native RCs, in the M266HL we observed a biphasicity of the P + AQ A -f PAQ A charge recombination. Interestingly, both phases present a similar acceleration in the M266HL mutant with respect to the wild type. The pH dependencies of the proton uptake upon Q A -and Q B -formations are superimposable in both mutants but very different from those of native RCs. The data measured in mutants are similar to those that we previously obtained on strains modified at various sites of the cytoplasmic region. The similarity of the response to these different mutations is puzzling, and we propose that it arises from a collective behavior of multiple acidic residues resulting in strongly anticooperative proton binding. The unspecific disappearance of the high pH band of proton uptake observed in all these mutants appears as the natural consequence of removing any member of an interactive proton cluster. This long range interaction also accounts for the similar responses to mutations of the proton uptake pattern induced by either Q A -or Q B -. We surmise that the presence of an extended protonated water H-bond network providing protons to Q B is responsible for these effects.Bacterial reaction centers (RCs 1 ) convert light excitation energy into chemical free energy in a similar way as the photosystem II of oxygen evolving complexes (1). RCs are membrane proteins composed of three subunits, L, M, and H, with a total molecular weight of about 100 kDa. The initial electronic excitation of a dimer of bacteriochlorophylls, P, situated on the periplasmic side of the RCs produces its electronic excited singlet state of lowest energy P*. Within about 200 ps an electron is sent from P* Via intermediate carriers (a monomer of bacteriochlorophyll and a bacteriopheophytin, H) to a ubiquinone acceptor named Q A , located on the cytoplasmic side of the complex. The electron is then transferred, in the hundred microseconds time scale, to the seconda...

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Charge recombination from the P+Q−A state in reaction centers from Rhodopseudomonas viridis

Cited by 92 publications

References 40 publications

Very fast electron transfer from cytochrome to the bacterial photosynthetic reaction center at low temperature

Very fast electron transfer from cytochrome to the bacterial photosynthetic reaction center at low temperature

Trapping Conformational Intermediate States in the Reaction Center Protein from Photosynthetic Bacteria

Evidence for Delocalized Anticooperative Flash Induced Proton Binding as Revealed by Mutants at the M266His Iron Ligand in Bacterial Reaction Centers

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