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Wraight CA. Roderick K. Clayton: a life, and some personal recollections. PHOTOSYNTHESIS RESEARCH 2014; 120:9-26. [PMID: 24254320 DOI: 10.1007/s11120-013-9948-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2013] [Accepted: 10/21/2013] [Indexed: 06/02/2023]
Abstract
Roderick K. Clayton passed away on October 23, 2011, at the age of 89, shortly after the plan for this dedicatory issue of Photosynthesis Research had been hatched. I had just written a lengthy letter to him to re-establish contact after a hiatus of 2 or 3 years, and to suggest that I visit him to talk about his life. It isn't clear whether he saw the letter or not, but it was found at his home in Santa Rosa, California. Fortunately, Rod has written two memoirs for Photosynthesis Research that not only cover much of his research on reaction centers (Photosynth Res 73:63-71, 2002) but also provide a humorous and honest look at his personal life (Photosynth Res 19:207-224, 1988). I cannot hope to improve on these and will try, instead, to fill in some of the gaps that Rod's own writing has left, and offer some of my own personal recollections over the more recent years.
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Affiliation(s)
- Colin A Wraight
- Department of Biochemistry and Center for Biophysics & Computational Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA,
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Zhang X, Gunner MR. Affinity and activity of non-native quinones at the Q(B) site of bacterial photosynthetic reaction centers. PHOTOSYNTHESIS RESEARCH 2014; 120:181-96. [PMID: 23715773 PMCID: PMC4442677 DOI: 10.1007/s11120-013-9850-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Accepted: 05/08/2013] [Indexed: 05/11/2023]
Abstract
Purple, photosynthetic reaction centers from Rhodobacter sphaeroides bacteria use ubiquinone (UQ10) as both primary (Q(A)) and secondary (Q(B)) electron acceptors. Many quinones reconstitute Q(A) function, while a few will act as Q(B). Nine quinones were tested for their ability to bind and reconstitute Q(A) and Q(B) functions. Only ubiquinone (UQ) reconstitutes both functions in the same protein. The affinities of the non-native quinones for the Q(B) site were determined by a competitive inhibition assay. The affinities of benzoquinones, naphthoquinone (NQ), and 2-methyl-NQ for the Q(B) site are 7 ± 3 times weaker than that at Q(A) site. However, di-ortho-substituted NQs and anthraquinone bind tightly to the Q(A) site (K d ≤ 200 nM), and ≥1,000 times more weakly to the Q(B) site, perhaps setting a limit on the size of the site. With a low-potential electron donor, 2-methyl, 3-dimethylamino-1,4-NQ, (Me-diMeAm-NQ) at Q(A), Q(B) reduction is 260 meV, more favorable than with UQ as Q(A). Electron transfer from Me-diMeAm-NQ at the Q(A) site to NQ at the Q(B) site can be detected. In the Q(B) site, the NQ semiquinone is estimated to be ≈60-100 meV higher in energy than the UQ semiquinone, while in the Q(A) site, the semiquinone energy level is similar or lower with NQ than with UQ. Thus, the NQ semiquinone is more stable in the Q(A) than in the Q(B) site. In contrast, the native UQ semiquinone is ≈60 meV lower in energy in the Q(B) than in the Q(A) site, stabilizing forward electron transfer from Q(A) to Q(B).
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Affiliation(s)
| | - M. R. Gunner
- To whom correspondence should be addressed. Telephone: 212-650-5557. Fax: 212-650-6940
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Effects of dehydration on light-induced conformational changes in bacterial photosynthetic reaction centers probed by optical and differential FTIR spectroscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1827:328-39. [PMID: 23103449 DOI: 10.1016/j.bbabio.2012.10.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Revised: 10/16/2012] [Accepted: 10/19/2012] [Indexed: 11/22/2022]
Abstract
Following light-induced electron transfer between the primary donor (P) and quinone acceptor (Q(A)) the bacterial photosynthetic reaction center (RC) undergoes conformational relaxations which stabilize the primary charge separated state P(+)Q(A)(-). Dehydration of RCs from Rhodobacter sphaeroides hinders these conformational dynamics, leading to acceleration of P(+)Q(A)(-) recombination kinetics [Malferrari et al., J. Phys. Chem. B 115 (2011) 14732-14750]. To clarify the structural basis of the conformational relaxations and the involvement of bound water molecules, we analyzed light-induced P(+)Q(A)(-)/PQ(A) difference FTIR spectra of RC films at two hydration levels (relative humidity r=76% and r=11%). Dehydration reduced the amplitude of bands in the 3700-3550cm(-1) region, attributed to water molecules hydrogen bonded to the RC, previously proposed to stabilize the charge separation by dielectric screening [Iwata et al., Biochemistry 48 (2009) 1220-1229]. Other features of the FTIR difference spectrum were affected by partial depletion of the hydration shell (r=11%), including contributions from modes of P (9-keto groups), and from NH or OH stretching modes of amino acidic residues, absorbing in the 3550-3150cm(-1) range, a region so far not examined in detail for bacterial RCs. To probe in parallel the effects of dehydration on the RC conformational relaxations, we analyzed by optical absorption spectroscopy the kinetics of P(+)Q(A)(-) recombination following the same photoexcitation used in FTIR measurements (20s continuous illumination). The results suggest a correlation between the observed FTIR spectral changes and the conformational rearrangements which, in the hydrated system, strongly stabilize the P(+)Q(A)(-) charge separated state over the second time scale.
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Malferrari M, Francia F, Venturoli G. Coupling between Electron Transfer and Protein–Solvent Dynamics: FTIR and Laser-Flash Spectroscopy Studies in Photosynthetic Reaction Center Films at Different Hydration Levels. J Phys Chem B 2011; 115:14732-50. [DOI: 10.1021/jp2057767] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- Marco Malferrari
- Laboratorio di Biochimica e Biofisica, Dipartimento di Biologia, Università di Bologna, 40126 Bologna, Italy
| | - Francesco Francia
- Laboratorio di Biochimica e Biofisica, Dipartimento di Biologia, Università di Bologna, 40126 Bologna, Italy
| | - Giovanni Venturoli
- Laboratorio di Biochimica e Biofisica, Dipartimento di Biologia, Università di Bologna, 40126 Bologna, Italy
- Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, c/o Dipartimento di Fisica, Università di Bologna, 40127 Bologna, Italy
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Savitsky A, Malferrari M, Francia F, Venturoli G, Möbius K. Bacterial Photosynthetic Reaction Centers in Trehalose Glasses: Coupling between Protein Conformational Dynamics and Electron-Transfer Kinetics as Studied by Laser-Flash and High-Field EPR Spectroscopies. J Phys Chem B 2010; 114:12729-43. [DOI: 10.1021/jp105801q] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Anton Savitsky
- Max-Planck-Institut für Bioanorganische Chemie, 45470 Mülheim an der Ruhr, Germany, Laboratorio di Biochimica e Biofisica, Dipartimento di Biologia, Università di Bologna, 40126 Bologna, Italy, Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, c/o Dipartimento di Fisica, Università di Bologna, 40127 Bologna, Italy, and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Marco Malferrari
- Max-Planck-Institut für Bioanorganische Chemie, 45470 Mülheim an der Ruhr, Germany, Laboratorio di Biochimica e Biofisica, Dipartimento di Biologia, Università di Bologna, 40126 Bologna, Italy, Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, c/o Dipartimento di Fisica, Università di Bologna, 40127 Bologna, Italy, and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Francesco Francia
- Max-Planck-Institut für Bioanorganische Chemie, 45470 Mülheim an der Ruhr, Germany, Laboratorio di Biochimica e Biofisica, Dipartimento di Biologia, Università di Bologna, 40126 Bologna, Italy, Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, c/o Dipartimento di Fisica, Università di Bologna, 40127 Bologna, Italy, and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Giovanni Venturoli
- Max-Planck-Institut für Bioanorganische Chemie, 45470 Mülheim an der Ruhr, Germany, Laboratorio di Biochimica e Biofisica, Dipartimento di Biologia, Università di Bologna, 40126 Bologna, Italy, Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, c/o Dipartimento di Fisica, Università di Bologna, 40127 Bologna, Italy, and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
| | - Klaus Möbius
- Max-Planck-Institut für Bioanorganische Chemie, 45470 Mülheim an der Ruhr, Germany, Laboratorio di Biochimica e Biofisica, Dipartimento di Biologia, Università di Bologna, 40126 Bologna, Italy, Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, c/o Dipartimento di Fisica, Università di Bologna, 40127 Bologna, Italy, and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany
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Francia F, Malferrari M, Sacquin-Mora S, Venturoli G. Charge Recombination Kinetics and Protein Dynamics in Wild Type and Carotenoid-less Bacterial Reaction Centers: Studies in Trehalose Glasses. J Phys Chem B 2009; 113:10389-98. [DOI: 10.1021/jp902287y] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Francesco Francia
- Laboratorio di Biochimica e Biofisica, Dipartimento di Biologia, Università di Bologna, 40126 Bologna, Italy, Laboratoire de Biochimie Théorique, CNRS UPR 9080, Institut de Biologie Physico-Chimique, 75005 Paris, France, and Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia (CNISM), Bologna, Italy
| | - Marco Malferrari
- Laboratorio di Biochimica e Biofisica, Dipartimento di Biologia, Università di Bologna, 40126 Bologna, Italy, Laboratoire de Biochimie Théorique, CNRS UPR 9080, Institut de Biologie Physico-Chimique, 75005 Paris, France, and Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia (CNISM), Bologna, Italy
| | - Sophie Sacquin-Mora
- Laboratorio di Biochimica e Biofisica, Dipartimento di Biologia, Università di Bologna, 40126 Bologna, Italy, Laboratoire de Biochimie Théorique, CNRS UPR 9080, Institut de Biologie Physico-Chimique, 75005 Paris, France, and Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia (CNISM), Bologna, Italy
| | - Giovanni Venturoli
- Laboratorio di Biochimica e Biofisica, Dipartimento di Biologia, Università di Bologna, 40126 Bologna, Italy, Laboratoire de Biochimie Théorique, CNRS UPR 9080, Institut de Biologie Physico-Chimique, 75005 Paris, France, and Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia (CNISM), Bologna, Italy
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The redox midpoint potential of the primary quinone of reaction centers in chromatophores of Rhodobacter sphaeroides is pH independent. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2008; 37:1207-17. [DOI: 10.1007/s00249-008-0301-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2007] [Revised: 02/11/2008] [Accepted: 03/02/2008] [Indexed: 10/22/2022]
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Dezi M, Francia F, Mallardi A, Colafemmina G, Palazzo G, Venturoli G. Stabilization of charge separation and cardiolipin confinement in antenna-reaction center complexes purified from Rhodobacter sphaeroides. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2007; 1767:1041-56. [PMID: 17588528 DOI: 10.1016/j.bbabio.2007.05.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2007] [Revised: 05/19/2007] [Accepted: 05/22/2007] [Indexed: 10/23/2022]
Abstract
The reaction center-light harvesting complex 1 (RC-LH1) purified from the photosynthetic bacterium Rhodobacter sphaeroides has been studied with respect to the kinetics of charge recombination and to the phospholipid and ubiquinone (UQ) complements tightly associated with it. In the antenna-RC complexes, at 6.5<pH<9.0, P(+)Q(B)(-) recombines with a pH independent average rate constant <k> more than three times smaller than that measured in LH1-deprived RCs. At increasing pH values, for which <k> increases, the deceleration observed in RC-LH1 complexes is reduced, vanishing at pH >11.0. In both systems kinetics are described by a continuous rate distribution, which broadens at pH >9.5, revealing a strong kinetic heterogeneity, more pronounced in the RC-LH1 complex. In the presence of the antenna the Q(A)Q(B)(-) state is stabilized by about 40 meV at 6.5<pH<9.0, while it is destabilized at pH >11. The phospholipid/RC and UQ/RC ratios have been compared in chromatophore membranes, in RC-LH1 complexes and in the isolated peripheral antenna (LH2). The UQ concentration in the lipid phase of the RC-LH1 complexes is about one order of magnitude larger than the average concentration in chromatophores and in LH2 complexes. Following detergent washing RC-LH1 complexes retain 80-90 phospholipid and 10-15 ubiquinone molecules per monomer. The fractional composition of the lipid domain tightly bound to the RC-LH1 (determined by TLC and (31)P-NMR) differs markedly from that of chromatophores and of the peripheral antenna. The content of cardiolipin, close to 10% weight in chromatophores and LH2 complexes, becomes dominant in the RC-LH1 complexes. We propose that the quinone and cardiolipin confinement observed in core complexes reflects the in vivo heterogeneous distributions of these components. Stabilization of the charge separated state in the RC-LH1 complexes is tentatively ascribed to local electrostatic perturbations due to cardiolipin.
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Affiliation(s)
- Manuela Dezi
- Dipartimento di Biologia, Laboratorio di Biochimica e Biofisica, Università di Bologna, 40126 Bologna, Italy
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Gast P, Michalski T, Hunt J, Norris J. Determination of the amount and the type of quinones present in single crystals from reaction center protein from the photosynthetic bacterium Rhodopseudomonas viridis. FEBS Lett 2001. [DOI: 10.1016/0014-5793(85)80544-5] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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McPherson PH, Okamura MY, Feher G. Light-induced proton uptake by photosynthetic reaction centers from Rhodobacter sphaeroides R-26.1. II. Protonation of the state DQAQB2-. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1144:309-24. [PMID: 8399281 DOI: 10.1016/0005-2728(93)90116-w] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Proton uptake associated with the two-electron reduction of QB was investigated in reaction centers (RCs) from Rhodobacter sphaeroides R-26.1 using pH-sensitive dyes. An uptake of two protons was observed at pH < or = 7.5, consistent with the formation of the dihydroquinone QBH2. At higher pH, the proton uptake decreased with an apparent pKa of approx. 8.5, i.e., to 1.5 H+/2 e- at pH 8.5. A molecular model is presented in which the apparent pKa is due to the protonation of either the carbonyl oxygen on QB or of an amino acid residue near QB (e.g., His-L190). Experimental evidence in favor of the protonation of the oxygen is discussed. The kinetics of the electron transfer from QA-QB- to QAQB2- and the associated proton uptake were compared at several pH values and temperatures. At pH 8.5 (21.5 degrees C) the rate constants for the proton uptake and electron transfer are the same within the precision of the measurement. At lower pH, the proton uptake rate constant is smaller than that for electron transfer. The difference between the rate constants is temperature dependent, i.e., it varies from 12 +/- 4% at 21.5 degrees C (pH 7.5) to 28 +/- 4% at 4.0 degrees C (pH 7.5). We show that the kinetics can be explained by a previously proposed model (Paddock, M. L., McPherson, P. H., Feher, G. and Okamura, M. Y. (1990) Proc. Natl. Acad. Sci. USA 87, 6803-6807) in which the uptake of two protons by doubly reduced QB occurs sequentially, one concomitant with and the other after electron transfer.
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Affiliation(s)
- P H McPherson
- Department of Physics, University of California at San Diego, La Jolla 92093-0319
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Maróti P. Flash-induced proton transfer in photosynthetic bacteria. PHOTOSYNTHESIS RESEARCH 1993; 37:1-17. [PMID: 24317650 DOI: 10.1007/bf02185435] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/1992] [Accepted: 03/27/1993] [Indexed: 06/02/2023]
Abstract
A proton electrochemical potential across the membranes of photosynthetic purple bacteria is established by a light-driven proton pump mechanism: the absorbed light in the reaction center initiates electron transfer which is coupled to the vectorial displacement of protons from the cytoplasm to the periplasm. The stoichiometry and kinetics of proton binding and release can be tracked directly by electric (glass electrodes), spectrophotometric (pH indicator dyes) and conductimetric techniques. The primary step in the formation of the transmembrane chemiosmotic potential is the uptake of two protons by the doubly reduced secondary quinone in the reaction center and the subsequent exchange of hydroquinol for quinone from the membrane quinone-pool. However, the proton binding associated with singly reduced promary and/or secondary quinones of the reaction center is substoichiometric, pH-dependent and its rate is electrostatically enhanced but not diffusion limited. Molecular details of protonation are discussed based on the crystallographic structure of the reaction center of purple bacteriaRb. sphaeroides andRps. viridis, structure-based molecular (electrostatic) calculations and mutagenesis directed at protonatable amino acids supposed to be involved in proton conduction pathways.
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Affiliation(s)
- P Maróti
- Institute of Biophysics, József Attila University Szeged, Egyetem utca 2, H-6722, Szeged, Hungary
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Witt HT. Functional mechanism of water splitting photosynthesis. PHOTOSYNTHESIS RESEARCH 1991; 29:55-77. [PMID: 24415108 DOI: 10.1007/bf00035377] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/1991] [Accepted: 06/10/1991] [Indexed: 06/03/2023]
Abstract
A personal account is given on physico-chemical aspects of photosynthesis. The article starts with the way I entered the field of photosynthesis. Then, selected results from our research group are discussed. Three methods used for functional analysis in our laboratory are described: the repetitive flash spectroscopy; the electrochromic volt- and ammeter; and the membrane energization by a battery. Our subsequent studies deal with the two photoreaction centers, the primary charge separation, the plastoquinones as a transmembrane link between the two centers and the vectorial electron- and proton pathways. The results led to a picture of the elementary functional mechanism of the molecular machinery in the thylakoid membrane. The perspective then focuses on the coupling between the electric field, protons and phosphorylation. This section is followed by our observations and analysis of the mechanism of water cleavage and its coupling with the functioning of reaction center II. Finally, information is provided on structural aspects of the two reaction centers. The article ends with a retrospect.
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Affiliation(s)
- H T Witt
- Max-Volmer-Institut für Biophysikalische und Physikalische Chemie, Technische Universität Berlin, Straße des 17. Juni 135, D-1000, Berlin 12, Germany
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McPherson P, Okamura M, Feher G. Light-induced proton uptake by photosynthetic reaction centers from Rhodobacter sphaeroides R-26. I. Protonation of the one-electron states D+QA−, DQA−, D+QAQB−, and DQAQB−. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1988. [DOI: 10.1016/0005-2728(88)90093-x] [Citation(s) in RCA: 118] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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van der Wal HN, van Grondelle R, Millett F, Knaff DB. Oxidation of cytochrome c2 and of cytochrome c by reaction centers of Rhodospirillum rubrum and Rhodobacter sphaeroides. The effect of ionic strength and of lysine modification on oxidation rates. BIOCHIMICA ET BIOPHYSICA ACTA 1987; 893:490-8. [PMID: 2820485 DOI: 10.1016/0005-2728(87)90100-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The oxidation of cytochrome c2 by the photooxidized reaction center bacteriochlorophyll, P+-870, in chromatophores of Rhodospirillum rubrum can be described using second-order kinetics at all ionic strengths. In a system consisting of isolated R. rubrum reaction centers and purified R. rubrum cytochrome c2, the oxidation of cytochrome c2 also follows second-order kinetics. In both cases, the reaction rates at low ionic strength are weakly dependent on the ionic strength. The data suggest that the cytochrome remains mobile at very low ionic strength, since the observed kinetics can be easily explained assuming no significant tight binding of cytochrome c2 to the reaction center. In a system consisting of equine cytochrome c and reaction centers of either R. rubrum or Rhodobacter sphaeroides, the cytochrome c oxidation rate depends more strongly on the ionic strength. The high reaction rates at low ionic strength suggest that a significant portion of the cytochrome is bound. Using equine cytochrome c derivatives modified at specific lysine residues, it was shown that both R. rubrum and Rb. sphaeroides reaction centers react with equine cytochrome c through its exposed heme edge.
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Affiliation(s)
- H N van der Wal
- Department of Biophysics, Huygens Laboratory of the State University, Leiden, The Netherlands
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Kleinfeld D, Okamura MY, Feher G. Charge recombination kinetics as a probe of protonation of the primary acceptor in photosynthetic reaction centers. Biophys J 1985; 48:849-52. [PMID: 3907729 PMCID: PMC1329411 DOI: 10.1016/s0006-3495(85)83844-3] [Citation(s) in RCA: 37] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The kinetics of the charge recombination D+QA-----DQA was used to probe the protonation of the primary acceptor in reaction centers from Rhodopseudomonas sphaeroides, in which the native ubiquinone was replaced by anthraquinone. We found that QA- is stabilized by the rapid (t less than 10(-2) s) binding of a proton, with a pK of 9.8. The distance between QA- and the proton binding site was estimated to be larger than approximately 5 A.
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de Groot A, Lous EJ, Hoff AJ. Magnetic interactions between the triplet state of the primary donor and the prereduced ubiquinone acceptor in reaction centers of the photosynthetic bacterium Rhodopseudomonas sphaeroides 2.4.1. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1985. [DOI: 10.1016/0005-2728(85)90022-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Hoff A, den Blanken H, Vasmel H, Meiburg R. Linear-dichroic triplet-minus-singlet absorbance difference spectra of reaction centers of the photosynthetic bacteria Chromatium vinosum, Rhodopseudomonas sphaeroides R-26 and Rhodospirillum rubrum S1. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1985. [DOI: 10.1016/0005-2728(85)90246-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Butler WF, Calvo R, Fredkin DR, Isaacson RA, Okamura MY, Feher G. The electronic structure of Fe2+ in reaction centers from Rhodopseudomonas sphaeroides. III. EPR measurements of the reduced acceptor complex. Biophys J 1984; 45:947-73. [PMID: 6329347 PMCID: PMC1434980 DOI: 10.1016/s0006-3495(84)84241-1] [Citation(s) in RCA: 120] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Electron paramagnetic resonance (EPR) spectra of the reduced quinone-iron acceptor complex in reaction centers were measured in a variety of environments and compared with spectra calculated from a theoretical model. Spectra were obtained at microwave frequencies of 1, 9, and 35 GHz and at temperatures from 1.4 to 30 K. The spectra are characterized by a broad absorption peak centered at g = 1.8 with wings extending from g approximately equal to 5 to g less than 0.8. The peak is split with the low-field component increasing in amplitude with temperature. The theoretical model is based on a spin Hamiltonian, in which the reduced quinone, Q-, interacts magnetically with Fe2+. In this model the ground manifold of the interacting Q-Fe2+ system has two lowest doublets that are separated by approximately 3 K. Both perturbation analyses and exact numerical calculations were used to show how the observed spectrum arises from these two doublets. The following spin Hamiltonian parameters optimized the agreement between simulated and observed spectra: the electronic g tensor gFe, x = 2.16, gFe, y = 2.27, gFez = 2.04, the crystal field parameters D = 7.60 K and E/D = 0.25, and the antiferromagnetic magnetic interaction tensor, Jx = -0.13 K, Jy = -0.58 K, Jz = -0.58 K. The model accounts well for the g value (1.8) of the broad peak, the observed splitting of the peak, the high and low g value wings, and the observed temperature dependence of the shape of the spectra. The structural implications of the value of the magnetic interaction, J, and the influence of the environment on the spin Hamiltonian parameters are discussed. The similarity of spectra and relaxation times observed from the primary and secondary acceptor complexes Q-AFe2+ and Fe2+Q-B leads to the conclusion that the Fe2+ is approximately equidistant from QA and QB.
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Magnetic field-stimulated luminescence and a matrix model for energy transfer. A new method for determining the redox state of the first quinone acceptor in the reaction center of whole cells of Rhodospirillum rubrum. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1983. [DOI: 10.1016/0005-2728(83)90184-6] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Agalidis I, Reiss-Husson F. Several properties of the LM unit extracted with sodium dodecyl sulfate from Rhodopseudomonas sphaeroides purified reaction centers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1983. [DOI: 10.1016/0005-2728(83)90093-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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22
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Evidence for an anisotropic magnetic interaction between the (bacteriopheophytin) intermediary acceptor and the first quinone acceptor in bacterial photosynthesis. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1983. [DOI: 10.1016/0005-2728(83)90008-7] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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23
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Erabi T, Tanaka M. Cathodic Reduction of Ubiquinone-10 Dissolved in Carbon-paste Electrode. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 1983. [DOI: 10.1246/bcsj.56.15] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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24
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Kendall-Tobias MW, Crofts AR. Primary and secondary electron transfer in hexane-solubilized proteolipid complexes of Rhodopseudomonas sphaeroides R-26. Biochem Biophys Res Commun 1981; 100:1444-52. [PMID: 6975099 DOI: 10.1016/0006-291x(81)90680-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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Swarthoff T, van der Veek-Horsley KM, Amesz J. The primary charge separation, cytochrome oxidation and triplet formation in preparations from the green photosynthetic bacterium Prosthecochloris aestuarii. BIOCHIMICA ET BIOPHYSICA ACTA 1981; 635:1-12. [PMID: 6260159 DOI: 10.1016/0005-2728(81)90002-5] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Flash-induced absorbance changes were measured in intact cells and subcellular preparations of the green photosynthetic bacterium Prosthecochloris aestuarii. In Complex I, a membrane vesicle preparation, photooxidation of the primary electron donor, P-840, and of cytochrome c-553 was observed. Flash excitation of the photosystem pigment complex caused in addition the generation of a bacteriochlorophyll a triplet. Triplet formation was the only reaction observed after flash excitation in the reaction center pigment-protein complex. The triplet had a lifetime of 90 microseconds at 295 K and of 165 microseconds at 120 K. The amount of triplet formed in a flash increased upon cooling from 295 to 120 K from 0.2 and 0.5 per reaction center to 0.45 and nearly 1 per reaction center in the photosystem pigment and reaction center pigment-protein complex, respectively. Measurements of absorbance changes in the near infrared in the reaction center pigment-protein complex indicate that the triplet is formed in the reaction center and that the reaction center bacteriochlorophyll a triplet is that of P-840. Formation of a carotenoid triplet did not occur in our preparations. Illumination with continuous light at 295 K of the reaction center pigment-protein complex produced a stable charge separation (with oxidation of P-840 and cytochrome c-553) in each reaction center, but with a low efficiency. This low efficiency, and the high yield of triplet formation is probably due to damage of the electron transport chain at the acceptor side of the reaction center of the reaction center pigment-protein complex. The halftime for cytochrome c-553 oxidation in Complex I and the photosystem pigment complex was 90 microseconds at 295 K; below 220 K no cytochrome oxidation occurred. At 120 K P-840+ was rereduced with a halftime of 20 ms, presumably by a back reaction with a reduced acceptor.
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Nikolaev GM, Knox PP, Kononenko AA, Grishanova NP, Rubin AB. Photo-induced electron transport and water state in Rhodospirillum rubrum chromatophores. BIOCHIMICA ET BIOPHYSICA ACTA 1980; 590:194-201. [PMID: 6768386 DOI: 10.1016/0005-2728(80)90024-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
It is shown that in bacterial chromatophores the pronounced changes in the free water content with a proton spin-spin relaxation time (T2) of 10(-3)--10(-2) s does not influence the efficiency of electron transfer from the photosynthetic reaction centre to the membrane pool of secondary acceptors. An abrupt inhibition of this process occurs only after the loss of the water with faster proton spin-spin relaxation time (T2 of 10(-4) s). The process is reversible. The water fraction in question is obviously bound to the chromatophore proteins and forms the primary hydration layer.
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[15] Bacterial reaction center (RC) and photoreceptor complex (PRC) preparations. Methods Enzymol 1980. [DOI: 10.1016/s0076-6879(80)69017-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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31
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Futami A, Hauska G. Vectorial redox reactions of physiological quinones. II. A study of transient semiquinone formation. BIOCHIMICA ET BIOPHYSICA ACTA 1979; 547:597-608. [PMID: 486436 DOI: 10.1016/0005-2728(79)90036-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Transient absorption changes during reduction of quinone in liposomes by external dithionite, in the absence and presence of initially trapped ferricyanide, were matched with absorption spectra of semiquinone and quinone in the blue region. Plastoquinone, ubiquinone-9 and phylloquinone, each having an isoprenoid side chain were compared with trimethyl-p-benzoquinone, ubiquinone-9 and menadione, which lack a long side chain. Semiquinone transients could only be observed by our spectroscopic technique during reduction of quinones lacking the chain. If Triton X-100 was added to the liposomes preparation semiquinone transients were also observed with the isoprenoid quinones. This result is consistent with the view that isoprenoid quinones build domains in the membranes, in which the life time of the semiquinone might be decreased by fast disproportionation, and to which dithionite has limited access.
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32
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Marinetti TD, Okamura MY, Feher G. Localization of the primary quinone binding site in reaction centers from Rhodopseudomonas sphaeroides R-26 by photoaffinity labeling. Biochemistry 1979; 18:3126-33. [PMID: 223628 DOI: 10.1021/bi00581a033] [Citation(s) in RCA: 38] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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33
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Blankenship RE, Parson WW. The involvement of iron and ubiquinone in electron transfer reactions mediated by reaction centers from photosynthetic bacteria. BIOCHIMICA ET BIOPHYSICA ACTA 1979; 545:429-44. [PMID: 311656 DOI: 10.1016/0005-2728(79)90152-x] [Citation(s) in RCA: 83] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Reaction centers from Rhodopseudomonas sphaeroides strain R-26 were prepared with varying Fe and ubiquinone (Q) contents. The photooxidation of P-870 to P-870+ was found to occur with the same quantum yield in Fe-depleted reaction centers as in control samples. The kinetics of electron transfer from the initial electron acceptor (I) to Q also were unchanged upon Fe removal. We conclude that Fe has no measurable role in the primary photochemical reaction. The extent of secondary reaction from the first quinone acceptor (QA) to the second quinone acceptor (QB) was monitored by the decay kinetics of P-870+ after excitation of reaction centers with single flashes in the absence of electron donors, and by the amount of P-870 photooxidation that occurred on the second flash in the presence of electron donors. In reaction centers with nearly one iron and between 1 and 2 ubiquinones per reaction center, the amount of secondary electron transfer is proportional to the ubiquinone content above one per reaction center. In reaction centers treated with LiClO4 and o-phenanthroline to remove Fe, the amount of secondary reaction is decreased and is proportional to Fe content. Fe seems to be required for the secondary reaction. In reaction centers depleted of Fe by treatment with SDS and EDTA, the correlation between Fe content and secondary activity is not as good as that found using LiClO4. This is probably due in part to a loss of primary photochemical activity in samples treated with SDS; but the correlation is still not perfect after correction for this effect. The nature of the back reaction between P-870+ and Q-B was investigated using stopped flow techniques. Reaction centers in the P-870+ Q-B state decay with a 1-s half-time in both the presence and absence of o-phenanthroline, an inhibitor of electron transfer between Q-B and QB. This indicates that the back reaction between P-870+ and Q-A is direct, rather than proceeding via thermal repopulation of Q-A. The P-870+ Q-B state is calculated to lie at least 100 mV in free energy below the P-870+ Q-A state.
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de Grooth BG, van Grondelle R, Romijn JC, Pulles MP. The mechanism of reduction of the ubiquinone pool in photosynthetic bacteria at different redox potentials. BIOCHIMICA ET BIOPHYSICA ACTA 1978; 503:480-90. [PMID: 99172 DOI: 10.1016/0005-2728(78)90147-0] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
(1) A flash number dependency of flash-induced absorbance changes was observed with whole cells of Rhodospirillum rubrum and chromatophores of R. rubrum and Rhodopseudomonas sphaeroides wild type and the G1C mutant. The oscillatory behavior was dependent on the redox potential; it was observed under oxidizing conditions only. Absorbance difference spectra measured after each flash in the 275--500 nm wavelength region showed that a molecule of ubiquinone, R, is reduced to the semiquinone (R-) after odd-numbered flashes and reoxidized after even-numbered flashes. The amount of R reduced was approximately one molecule per reaction center. (2) The flash number dependency of the electrochromic shift of the carotenoid spectrum was studied with chromatophores of Rps. sphaeroides wild type and the G1C mutant. At higher values of the ambient redox potential a relatively slow phase with a rise time of 30 ms was observed after even-numbered flashes, in addition to the fast phase (completed within 0.2 ms) occurring after each flash. Evidence was obtained that the slow phase represents the formation of an additional membrane potential during a dark reaction that occurs after flashes with an even number. This reaction is inhibited by antimycin A, whereas the oscillations of the R/R- absorbance changes remain unaffected. At low potentials (E = 100 mV) no oscillations of the carotenoid shift were observed: a fast phase was followed by a slow phase (antimycin-sensitive) with a half-time of 3 ms after each flash. (3) The results are discussed in terms of a model for the cyclic electron flow as described by Prince and Dutton (Prince, R.C. and Dutton, P.L. (1976) Bacterial Photosynthesis Conference, Brussels, Belgium, September 6--9, Abstr. TB4) employing the so-called Q-cycle.
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Holten D, Windsor MW, Parson WW, Thornber JP. Primary photochemical processes in isolated reaction centers of Rhodopseudomonas viridis. BIOCHIMICA ET BIOPHYSICA ACTA 1978; 501:112-26. [PMID: 620009 DOI: 10.1016/0005-2728(78)90100-7] [Citation(s) in RCA: 185] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Picosecond and nanosecond spectroscopic techniques have been used to study the primary electron transfer processes in reaction centers isolated from the photosynthetic bacterium Rhodopseudomonas viridis. Following flash excitation, the first excited singlet state (P*) of the bacteriochlorophyll complex (P) transfers an electron to an intermediate acceptor (I) in less than 20 ps. The radical pair state P+I-) subsequently transfers an electron to another acceptor (X) in about 230 ps. There is an additional step of unknown significance exhibiting 35 ps kinetics. P+ subsequently extracts an electron from a cytochrome, with a time constant of about 270 ns. At low redox potential (X reduced before the flash), the state P+I- (or PF) lives approx. 15 ns. It decays, in part, into a longer lived state (PR), which appears to be a triplet state. State PR decays with an exponential time of approx. 55 microseconds. After continuous illumination at low redox potential (I and X both reduced), excitation with an 8-ps flash produces absorption changes reflecting the formation of the first excited singlet state, P*. Most of P* then decays with a time constant of 20 ps. The spectra of the absorbance changes associated with the conversion of P to P* or P+ support the view that P involves two or more interacting bacteriochlorophylls. The absorbance changes associated with the reduction of I to I- suggest that I is a bacteriopheophytin interacting strongly with one or more bacteriochlorophylls in the reaction center.
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Bering CL, Loach PA. EFFECTS OF 2,5-DIBROMO-3-METHYL-6-ISOPROPYL BENZOQUINONE (DBMIB) ON PHOTOCHEMICAL EVENTS IN RHODOSPIRILLUM RUBRUM. Photochem Photobiol 1977. [DOI: 10.1111/j.1751-1097.1977.tb07540.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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37
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de Grooth BG, Amesz J. Electrochromic absorbance changes of photosynthetic pigments in Rhodopseudomonas sphaeroides. I. Stimulation by secondary electron transport at low temperature. BIOCHIMICA ET BIOPHYSICA ACTA 1977; 462:237-46. [PMID: 588564 DOI: 10.1016/0005-2728(77)90122-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Light-induced absorbance changes were measured at temperatures between --30 and --55 degrees C in chromatophores of Rhodopseudomonas sphaeroides. Absorbance changes due to photooxidation of reaction center bacteriochlorophyll (P-870) were accompanied by a red shift of the absorption bands of a carotenoid. The red shift was inhibited by gramicidin D. The kinetics of P-870 indicated electron transport from the "primary" to a secondary electron acceptor. This electron transport was slowed down by lowering the temperature or increasing the pH of the suspension. Electron transport from soluble cytochrome c to P-870+ occurred in less purified chromatophore preparations. This electron transport was accompanied by a relatively large increase of the carotenoid absorbance change. This agrees with the hypothesis that P-870 is located inside the membrane, so that an additional membrane potential is generated upon transfer of an electron from cytochrome to P-870+. A strong stimulation of the carotenoid changes (more than 10-fold in some experiments) and pronounced band shifts of bacteriochlorophyll B-850 were observed upon illumination in the presence of artifical donor-acceptor systems. Reduced N-methylphenazonium methosulphate (PMS) and N,N,N',N'-tetramethyl-p-phenylene-diamine (TMPD) were fairly efficient donors, whereas endogenous ubiquinone and oxidized PMS acted as secondary acceptor. These results indicate the generation of large membrane potentials at low temperature, caused by sustained electron transport across the chromatophore membrane. The artificial probe, merocyanine MC-V did not show electrochromic band shifts at low temperature.
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38
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Silberstein BR, Epel BL, Malkin S, Gromet-Elhanan Z. The effect of electron donors and acceptors on light-induced absorbance changes and photophosphorylation in Rhodospirillum rubrum chromatophores. EUROPEAN JOURNAL OF BIOCHEMISTRY 1977; 80:135-41. [PMID: 411652 DOI: 10.1111/j.1432-1033.1977.tb11865.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Light-induced difference spectra between 400 and 640 nm of Rhodospirillum rubrum chromatophores were performed in the presence and absence of exogenous electron donor/acceptor systems and compared with the chemical oxidation spectrum. The results indicate that the component previously defined as P430 is not a unique entity but rather represents different species, or a mixture of species, under various conditions. Under all conditions in which the reaction center bacteriochlorophyll is reversibly photooxidized, as indicated by the bleaching around 600 nm, it is also contributing to the absorbance increase around 430 nm. In one case, in presence of reduced dichloroindophenol and in the absence of oxygen, the photooxidation of reaction center bacteriochlorophyll is fully supressed. Under these conditions an irreversible change around 430 nm is still observed and seems to be due to the Soret band of b-type cytochrome. In the presence of reduced dichloroindophenol and absence of oxygen there is a marked inhibition of photophosphorylation. This inhibition is apparently due to the complete reduction of the cyclic electron carriers. Addition of the low potential dye benzyl viologen facilitates an almost complete recovery of the reversible photooxidation of reaction center bacteriochlorophyll as well as of photophosphorylation. These results indicate that the apparent mid-point potential of the primary electron acceptor in Rhodospirillum rubrum chromatophores is probably in the range of that of benzyl viologen (E'o = - 340 mV).
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Romijn JC, Amesz J. Purification and photochemical properties of reaction centers of Chromatium vinosum. Evidence for the photoreduction of a naphthoquinone. BIOCHIMICA ET BIOPHYSICA ACTA 1977; 461:327-38. [PMID: 901774 DOI: 10.1016/0005-2728(77)90223-7] [Citation(s) in RCA: 41] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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40
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Hoff AJ, Rademaker H, van Grondelle R, Duysens LN. On the magnetic field dependence of the yield of the triplet state in reaction centers of photosynthetic bacteria. BIOCHIMICA ET BIOPHYSICA ACTA 1977; 460:547-54. [PMID: 301748 DOI: 10.1016/0005-2728(77)90094-9] [Citation(s) in RCA: 112] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The yield of the triplet state in reaction centers of Rhodopseudomonas sphaeroides is dependent on the strength of an applied magnetic field. Reaction centers of the wild type that lack a functional iron complexed to the primary acceptor ubiquinone show a dependence similar to that of reaction centers of the mutant R-26 in which the iron-ubiquinone complex is intact. Apparently, the iron of the iron-ubiquinone complex is not essential to the effect, but it does exert an influence on its extent. Inchromatophores, the effect is about 2-fold decreased; the value of the magnetic field at which half the effect is found is about 500 G, in contrast to this value for reaction centers, which is 50--100 G. The magnetodependence of the triplet yield is discussed in terms of the Chemically Induced Dynamic Electron Polarization mechanism (CIDEP).
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41
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Wraight CA. Electron acceptors of photosynthetic bacterial reaction centers. Direct observation of oscillatory behaviour suggesting two closely equivalent ubiquinones. BIOCHIMICA ET BIOPHYSICA ACTA 1977; 459:525-31. [PMID: 191074 DOI: 10.1016/0005-2728(77)90051-2] [Citation(s) in RCA: 147] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
When reaction centers are illuminated by a series of single turnover flashes ubisemiquinone is formed and destroyed on alternate flashes. This oscillatory behaviour can be observed with both optical and electron spin resonance techniques. The oscillations are dependent upon the presence of excess ubiquinone in a manner which suggests that two molecules may act almost equivalently as metastable primary acceptors forming a two-electron gate between the one-electron primary photoact and a two-electron secondary acceptor pool.
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Vermeglio A. Secondary electron transfer in reaction centers of Rhodopseudomonas sphaeroides. Out-of-phase periodicity of two for the formation of ubisemiquinone and fully reduced ubiquinone. BIOCHIMICA ET BIOPHYSICA ACTA 1977; 459:516-24. [PMID: 300250 DOI: 10.1016/0005-2728(77)90050-0] [Citation(s) in RCA: 147] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Electron transfer between purified reaction centers from Rhodopseudomonas sphaeroides and exogenous ubiquinone has been studied in the presence of electron donors by measurements of light-induced absorbance changes following a sequence of short actinic light flashes. Each odd flash promotes the formation of a molecule of ubisemiquinone; after each even flash the semiquinone disappears and a molecule of the fully reduced quinone appears. We interpret these results by means of a model where a specialized molecule of ubiquinone is reduced by the primary electron acceptor in a one-electron transfer reaction after each flash, and is reoxidized by a molecule of the ubiquinone pool in a two-electron transfer reaction every two flashes.
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Hoff AJ, Gast P, Romijn JC. Time-resolved ESR and chemically induced dynamic electron polarisation of the primary reaction in a reaction center particle of Rhodopseudomonas sphaeroides wild type at low temperature. FEBS Lett 1977; 73:185-90. [PMID: 190035 DOI: 10.1016/0014-5793(77)80977-0] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Carithers RP, Parson WW. Delayed fluorescence from Rhodopseudomonas sphaeroides following single flashes. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 440:215-32. [PMID: 1084763 DOI: 10.1016/0005-2728(76)90125-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Delayed fluorescence from Rhodopseudomonas sphaeroides chromatophores was studied with the use of short flashes for excitation. Although the delayed fluorescence probably arises from a back-reaction between the oxidized reaction center bacteriochlorophyll complex (P+) and the reduced electron acceptor (X-), the decay of delayed fluorescence after a flash is much faster (tau1/2 approximately 120 mus) than the decay of P+X-. The rapid decay of delayed fluorescence is not due to the uptake of a proton from the solution, nor to a change in membrane potential. It correlates with small optical absorbance changes at 450 and 770 nm which could reflect a change in the state of X-. The intensity of the delayed fluorescence is 11-18-fold greater if the excitation flashes are spaced 2 s apart than it is if they are 30 s apart. The enhancement of delayed fluorescence at high flash repetition rates occurs only at redox potentials which are low enough (less than +240 mV) so that electron donors are available to reduce P+X- to PX- in part of the reaction center population. The enhancement decays between flashes as PX- is reoxidized to PX, as measured by the recovery of photochemical activity. Evidently, the reduction of P+X- to PX- leads to the storage of free energy that can be used on a subsequent flash to promote delayed fluorescence. The reduction of P+X- also is associated with a carotenoid spectral shift which decays as PX- is reoxidized to PX. Although this suggests that the free energy which supports the delayed fluorescence might be stored as a membrane potential, the ionophore gramicidin D only partially inhibits the enhancement of delayed fluorescence. With widely separated flashes, gramicidin has no effect on delayed fluorescence. At redox potentials low enough to keep X fully reduced, delayed fluorescence of the type described above does not occur, but one can detect weak luminescence which probably is due to phosphorescence of a protoporphyrin.
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Chamorovsky SK, Remennikov SM, Kononenko AA, Venediktov PS, Rubin AB. New experimental approach to the estimation of rate of electron transfer from the primary to secondary acceptors in the photosynthetic electron transport chain of purple bacteria. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 430:62-70. [PMID: 816385 DOI: 10.1016/0005-2728(76)90222-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
A method for calculating the rate constant (KA1A2) for the oxidation of the primary electron acceptor (A1) by the secondary one (A2) in the photosynthetic electron transport chain of purple bacteria is proposed. The method is based on the analysis of the dark recovery kinetics of reaction centre bacteriochlorophyll (P) following its oxidation by a short single laser pulse at a high oxidation-reduction potential of the medium. It is shown that in Ectothiorhodospira shaposhnikovii there is little difference in the value of KA1A2 obtained by this method from that measured by the method of Parson ((1969) Biochim, Biophys. Acta 189, 384-396), namely: (4.5 +/- 1.4)-10(3) s-1 and (6.9 +/- 1.2)-10(3) s-1, respectively. The proposed method has also been used for the estimation of the KA1A2 value in chromatophores of Rhodospirillum rubrum deprived of constitutive electron donors which are capable of reducing P+ at a rate exceeding this for the transfer of electron from A1 to A2. The method of Parson cannot be used in this case. The value of KA1A2 has been found to be (2.7 +/- 0.8)-10(3) s-1. The activation energies for the A1 to A2 electron transfer have also been determined. They are 12.4 kcal/mol and 9.9 kcal/mol for E. shaposhnikovii and R. rubrum, respectively.
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Zannoni D, Melandri BA, Baccarini-Melandri A. Energy transduction in photosynthetic bacteria. X. Composition and function of the branched oxidase system in wild type and respiration deficient mutants of Rhodopseudomonas capsulata. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 423:413-30. [PMID: 177045 DOI: 10.1016/0005-2728(76)90197-3] [Citation(s) in RCA: 79] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The respiratory chain of Rhodopseudomonas capsulata, strain St. Louis and of two respiration deficient mutants (M6 and M7) has been investigated by examining the redox and spectral characteristics of the cytochromes and their response to substrates and to specific respiratory inhibitors. Since the specific lesions of M6 and M7 have been localized on two different branches of the multiple oxidase system of the wild type strain, the capability for aerobic growth of these mutants can be considered as a proof of the physiological significance of both branched systems "in vivo". Using M6 and M7 mutants the response of the branched chain to respiratory inhibitors could be established. Cytochrome oxidase activity, a specific function of an high potential cytochrome b (E'0 = +413 mV) is sensitive to low concentrations of KCN (5-10(-5) M); CO is a specific inhibitor of an alternative oxidase, which is also inhibited by high concentrations of KCN (10(-3) M). Antimycin A inhibits preferentially the branch of the chain affected by low concentrations of cyanide. Redox titrations and spectral data indicate the presence in the membrane of three cytochromes of b type (E'0 = +413, +260, +47 vM) and two cytochromes of c type (E'0 = +342, +94 mV). A clear indication of the involvement in respiration of cytochrome b413, cytochrome c342 and cytochrome b47 has been obtained. Only 50% of the dithionite reducible cytochrome b can be reduced by respiratory substrates also in the presence of high concentrations of KCN or in anaerobiosis. The presence and function of quinones in the respiratory electron transport system has been clearly demonstrated. Quinones, which are reducible by NADH and succinate to about the same extent can be reoxidized through both branches of the respiratory chain, as shown by the response of their redox state to KCN. The possible site of the branching of the electron transport chain has been investigated comparing the per cent level of reduction of quinones and of cytochromes b and c as a function of KCN concentrations in membranes from wild type and M6 mutants cells. The site of the branching has been localized at the level of quinones-cytochrome b47. A tentative scheme of the respiratory chains operating in Rhodopseudomonas capsulata, St. Louis and in the two respiration deficient mutants, M6 and M7 is presented.
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Romijn JC, Amesz J. Photochemical activities of reaction centers from Rhodopseudomonas sphaeroides at low temperature and in the presence of chaotropic agents. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 423:164-73. [PMID: 174746 DOI: 10.1016/0005-2728(76)90175-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Light-induced absorbance changes were measured at low temperatures in reaction center preparations from Rhodopseudomonas sphaeroides. Absorbance difference spectra measured at 100 degrees K show that ubiquinone is photoreduced at this temperature, both by continuous light and by a short actinic flash. The reduction occurred with relatively high efficiency. These results give support to the idea that ubiquinone is involved in the primary photochemical reaction in Rhodopseudomonas sphaeroides. Reduction of ubiquinone was accompanied by a shift of the infrared absorption band of bacteriopheophytin. The rate of decay of the primary photoproducts (P+870 and ubisemiquinone) appeared to be approximately independent of temperature below 180 degrees K and above 270 degrees K; in the region between 180 and 270 degrees K it increased with decreasing temperature. The rate of decay was not affected by 0-phenanthroline. Secondary reactions were inhibited by lowering the temperature. The light-induced absorbance changes were inhibited by chaotropic agents, like thiocyanate and perchlorate. It was concluded that these agents lower the efficiency of the primary photoconversion. The kinetics indicated that the degree of inhibition was not the same for all reaction centers. The absorption spectrum of the photoconverted reaction centers appeared to be somewhat modified by thiocyanate.
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Okamura MY, Isaacson RA, Feher G. Primary acceptor in bacterial photosynthesis: obligatory role of ubiquinone in photoactive reaction centers of Rhodopseudomonas spheroides. Proc Natl Acad Sci U S A 1975; 72:3491-5. [PMID: 1081231 PMCID: PMC433020 DOI: 10.1073/pnas.72.9.3491] [Citation(s) in RCA: 358] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Reaction centers were found to bind two ubiquinones, both of which could be removed by o-phenanthroline and the detergent lauryldimethylamine oxide. One ubiquinone was more easily removed than the other. The low-temperature light-induced optical and electron paramagnetic resonance (EPR) changes were eliminated and restored upon removal and readdition of ubiquinone and were quantitatively correlated with the amount of tightly bound ubiquinone. We, therefore, conclude that this ubiquinone plays an obligatory role in the primary photochemistry. The easily removed ubiquinone is thought to be the secondary electron acceptor. The low-temperature charge recombination kinetics, as well as the optical and EPR spectra, were the same for untreated reaction centers and for those reconstituted with ubiquinone. This indicates that extraction and reconstitution were accomplished without altering the conformation of the active site. Reaction centers reconstituted with other quinones also showed restored photochemical activity, although they exhibited changes in their low-temperature recombination kinetics and light-induced (g = 1.8) EPR signal is interpreted in terms of a magnetically coupled ubiquinone--Fe2+ acceptor complex. A possible role of iron is to facilitate electron transfer between the primary and secondary ubiquinones.
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Wraight CA, Cogdell RJ, Clayton RK. Some experiments on the primary electron acceptor in reaction centres from Rhodopseudomonas sphaeroides. BIOCHIMICA ET BIOPHYSICA ACTA 1975; 396:242-9. [PMID: 168920 DOI: 10.1016/0005-2728(75)90038-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The bacterial reaction center absorbance change at 450 nm (A-450) assigned to an anionic semiquinone, has been suggested as a candidate for the reduced form of the primary electron acceptor in bacterial photosynthesis. In reaction centers of Rhodopseudomonas sphaeroides we have found kinetic discrepancies between the decay of A-450 and the recovery of photochemical competence. In addition, no proton uptake is measurable on the first turnover, although subsequent ones elicit one proton bound per electron. These results are taken to indicate that the acceptor reaction after a long dark period may be different for the first turnover than for subsequent ones. It is suggested that A-450 is still a likely candidate for the acceptor function but that in reaction centers, additional quinone may act as an adventitious primary acceptor when the "true" primary acceptor is reduced. Alternatively, the primary acceptor may act in a "ping-pong" fashion with respect to subsequent photoelectrons.
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