Charge recombination at low temperature in photosynthetic bacteria reaction centers: Evidence for two conformation states

Parot, Pierre; Thiéry, J.M.; Vermeglio, André

doi:10.1016/0005-2728(87)90105-8

Cited by 53 publications

(46 citation statements)

References 23 publications

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“…In Rb. sphaeroides, on the other hand, the opposite findings have been reported: nonexponential (4,26,30) and/or wavelength-dependent (26) P+Q-charge recombination kinetics at 77 K but exponential kinetics at 295 K. This has led to the proposal that the RC is trapped at low temperature in two conformations (26,30) or a distribution of conformations (4). The same conclusion has been reached from studies on RCs with prereduced BPhL (27) and from extensive low-temperature optically detected magnetic resonance studies (18,28).…”

Section: Methodsmentioning

confidence: 75%

Evidence that a distribution of bacterial reaction centers underlies the temperature and detection-wavelength dependence of the rates of the primary electron-transfer reactions.

Kirmaier

Holten

1990

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

194

113

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The rates of the primary electron-transfer processes in Rhodobacter sphaeroides reaction centers have been examined in detail by using 150-fs excitation flashes at 870 nm. At room temperature the apparent time constants for both initial charge separation (P* -> P+BPhj) and subsequent electron transfer (P+BPhj -+ P+QA) are found to encompass a range of values ('1.3-4 ps and "100-320 ps, respectively), depending on the wavelength at which the kinetics are followed.We suggest this reflects a distribution of reaction centers (or a few conformers), having differences in factors such as distances or orientations between the cofactors, hydrogen bonding, or other pigment-protein interactions. We also suggest that the time constants observed at cryogenic temperatures (""1.3 and "100 ps, respectively, with much smaller or negble variation with detection wavelength) do not reflect an actual increase in the rates with decreasing temperature but rather derive from a shift in the distribution of reaction centers toward those in which electron transfer inherently occurs with the faster rates.The temperature dependence of the rates of electron transfer in bacterial reaction centers (RCs) has received considerable experimental and theoretical attention. For the most part the temperature dependence of the initial charge separation step (observed to occur in ""3 ps at 295 K and 1 ps at 10 K) has been followed via the decay of the broad stimulated emission band of P*, which has a maximum near 920 nm in Rhodobacter sphaeroides (6, 7). The temperature dependence of electron transfer from BPhj to QA in Rb.sphaeroides (r 200 ps at 295 K and 100 ps at 77 K and below) similarly has been followed primarily in a single region, namely via decay of the broad BPhL anion band centered near 665 nm (5). Kinetics also have been measured at a few wavelengths near 800 nm in the recent studies of the P*-P+BPh-process, with the primary focus being a search for evidence for the possible transient reduction of the monomeric pigment BChlL (6,7,11,12). During the course of our previous investigations of electron transfer from BPhjL to QA, we examined the near-infrared (730-830 nm) region also, with the expectation of finding time constants that agreed with those measured via decay of the BPhL anion band. This proved not to be uniformly the case, however. At room temperature, for example, we found that at certain wavelengths the observed time constant was somewhat less than 200 ps, and at other wavelengths it was somewhat greater than 200 ps (5). A major limitation of these measurements was that the signal-to-noise ratio prevented a complete study in the near-infrared region in that accurate time constants at room temperature could be measured only within two narrow (-5 nm) wavelength regions centered near the peak ground state absorptions of the BPhs and the monomeric BChls.We have reexamined these findings by using instrumentation that gives a significantly better signal-to-noise ratio in AA and, in addition, utilizes 150-fs flashes (compared to...

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Section: Methodsmentioning

confidence: 75%

Evidence that a distribution of bacterial reaction centers underlies the temperature and detection-wavelength dependence of the rates of the primary electron-transfer reactions.

Kirmaier

Holten

1990

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

194

113

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“…The two possible contributions that we have considered to explain these earlier observations, and those of the present study, are supported by the results of other measurements. Namely, there may be structural changes in response to the new charge distribution resulting from electron transfer [44][45][46], and/or that there may be a distribution of protein conformations [47,48]. Both concepts are physically reasonable, and both may be manifest in various ways in the observed photochemistry.…”

Section: Lettersmentioning

confidence: 99%

Subpicosecond characterization of the optical properties of the primary electron donor and the mechanism of the initial electron transfer in Rhodobacter capsulatus reaction centers

Kirmaier

Holten

1988

FEBS Letters

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The optical difference spectrum of the excited primary electron donor, P*, in Rb. capsulatus reaction centers has been measured 600 fs after a 350‐fs flash at 870 nm. The spectrum is characterized by bleaching in the ground state absorption bands at 855 and 600 nm, and a weak featureless transient absorption in between. The lack of significant (if any) bleaching at 800 nm indicates that P does not contribute appreciable oscillator strength to the 800‐nm ground state absorption band. The conversion of P* to P+BPH− L is accompanied by isosbestic points in the transient difference spectra at 765 and 798 nm. The existence of the longer‐wavelength isosbestic point, occurring essentially at the near‐infrared absorbance maximum of the accessory BChls, provides compelling evidence that if state P*BChl− L forms, its transient concentration is exceedingly small. At certain wavelengths in the near‐infrared the absorption changes develop somewhat more slowly than the rate at which P* decays, a finding that may reflect a contribution from readjustments in the pigment‐protein complex in response to electron transfer.

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“…sphaeroides and R. rubrum, organisms that show monophasic kinetics at room temperature. This temperature-induced heterogeneity in the decay kinetics is thought to be due to the existence of 'fast' and 'slow' conformational RC states, possessing different rates of charge recombination and slightly distinct light-induced difference spectra [27,37]. At room temperature a fast equilibrium (compared to the recombination) occurs between these two conformational states, and the two states thus tend to follow a common monophasic recombination reaction [28].…”

Section: P +Q~ Charge Recombination Kinetics At Room Temperaturementioning

confidence: 99%

“…Besides the biphasic nature of P+QA charge recombination kinetics observed in Rps. viridis at room temperature, it has been reported [27,37] that lowering the temperature induces biphasicity of the P+QA charge recombination kinetics in Rb. sphaeroides and R. rubrum, organisms that show monophasic kinetics at room temperature.…”

Section: P +Q~ Charge Recombination Kinetics At Room Temperaturementioning

confidence: 99%

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Properties of the primary and secondary quinone electron acceptors in RC/LH1 complexes from the purple sulfur bacterium Ectothiorhodospira mobilis

Leguijt

Parot

Vermeglio

et al. 1993

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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Properties of the primary and secondary quinone electron acceptors in RC/LH1 complexes from the purple sulfur bacterium Ectothiorhodospira mobilis. Leguijt, T.; Parot, P.; Vermeglio, A.; Crielaard, W.; Hellingwerf, K.J. Published in:Biochimica et Biophysica Acta G General Subjects Link to publication Citation for published version (APA):Leguijt, T., Parot, P., Vermeglio, A., Crielaard, W., & Hellingwerf, K. J. (1994). Properties of the primary and secondary quinone electron acceptors in RC/LH1 complexes from the purple sulfur bacterium Ectothiorhodospira mobilis. Biochimica et Biophysica Acta G General Subjects, 1183, 292-300. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Reaction centers (RCs)with one antenna complex attached (RC/LH~ complexes)were isolated from the alkaliphilic and moderately halophilic, phototrophic purple sulfur bacterium Ectothiorhodospira (E.) mobilis and analyzed with respect to quinone composition and charge recombination kinetics, using time-resolved (low-and room-temperature) spectroscopy and thin-layer chromatography. The RCs contain menaquinone as primary and ubiquinone as secondary quinone electron acceptor, QA and Q a, respectively. Q B is lost during isolation of the RC/LH I complexes. P+ QA charge recombination kinetics, which were shown to be pH independent, were only slightly temperature dependent, indicating that this recombination proceeds via the direct (electron tunnelling) route. At room temperature, its average lifetime was 34.5 ms. These decay kinetics were shown to be monophasic at room temperature and biphasic at low temperature. Addition of an excess of UQ 6 to RC/LH I complexes resulted in retardation of the P+ recovery, due to charge recombination of the state P+QAQa. Functional reconstitution of QB was also evident from flash-induced binary oscillations at 450 nm, which could be observed in RC/LH I complexes in the presence of an excess of UQ 6. This reconstitution of QB activity was, however, incomplete and decreased with increasing pH. The P+QAQB decay kinetics were pH independent; the average lifetime was about 6 s at room temperature. The apparent equilibrium constant g 2 between the states QAQB and QAQB, and consequently the free energy difference between these states, were relatively large and pH independent...

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Charge recombination at low temperature in photosynthetic bacteria reaction centers: Evidence for two conformation states

Cited by 53 publications

References 23 publications

Evidence that a distribution of bacterial reaction centers underlies the temperature and detection-wavelength dependence of the rates of the primary electron-transfer reactions.

Evidence that a distribution of bacterial reaction centers underlies the temperature and detection-wavelength dependence of the rates of the primary electron-transfer reactions.

Subpicosecond characterization of the optical properties of the primary electron donor and the mechanism of the initial electron transfer in Rhodobacter capsulatus reaction centers

Properties of the primary and secondary quinone electron acceptors in RC/LH1 complexes from the purple sulfur bacterium Ectothiorhodospira mobilis

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