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Wasielewski MR, Norris JR, Shipman LL, Lin CP, Svec WA. Monomeric chlorophyll a enol: Evidence for its possible role as the primary electron donor in photosystem I of plant photosynthesis. Proc Natl Acad Sci U S A 2010; 78:2957-61. [PMID: 16593015 PMCID: PMC319478 DOI: 10.1073/pnas.78.5.2957] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The chlorophyll a (Chl a) special-pair model of the primary donor of photosystem I (P700) does not account in a completely adequate fashion for the magnetic resonance properties observed for P700(+). Moreover, P700 is at least 420 mV easier to oxidize than is Chl a in vitro. Neither Chl a dimer formation nor selective ligation of Chl a can account for this potential difference. Enolization of the Chl a ring V beta-keto ester results in a very different pi electronic structure. The Chl a enol can be trapped as a silyl enol ether. In addition, the enol analog 9-desoxo-9,10-dehydro-Chl a can be prepared. Both the trapped enol and its 9-H analog are approximately 350 mV easier to oxidize than Chl a. The ESR spectrum of the cation radical consists of a single 6.1-G gaussian line that is line narrowed relative to that of Chl a(+) in a manner similar to P700(+). Electron-nuclear double resonance (ENDOR) spectroscopy resolves only a 3.5-MHz hyperfine splitting for the 3-methyl-group. The remaining splittings are all less than 3.5 MHz. The second moment of the ESR line of fully (13)C-enriched 9-desoxo-9,10-dehydro-Chl a(+) agrees with that of [(13)C]P700(+) to within 10%. Application of the special-pair model to the [(13)C]P700(+) second-moment data yields a 100% error. Ab initio molecular orbital calculations on ethyl chlorophyllide a enol cation bear out the ESR and ENDOR data. We conclude that a monomeric Chl a enol model provides a better description of the magnetic resonance parameters and oxidation potential of P700 than a Chl a special-pair model.
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Affiliation(s)
- M R Wasielewski
- Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439
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Davis MS, Forman A, Fajer J. Ligated chlorophyll cation radicals: Their function in photosystem II of plant photosynthesis. Proc Natl Acad Sci U S A 2010; 76:4170-4. [PMID: 16592698 PMCID: PMC411532 DOI: 10.1073/pnas.76.9.4170] [Citation(s) in RCA: 142] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Magnesium tetraphenylchlorin, a synthetic model for chlorophyll, exhibits significant variations in the unpaired spin densities of its cation radicals with concomitant changes in oxidation potentials as a function of solvent and axial ligand. Similar effects are observed for chlorophyll (Chl) a and its cation radicals. Oxidation potentials for Chl --> Chl(+.) as high as +0.9 V (against a normal hydrogen electrode) are observed in nonaqueous solvents, with linewidths of the electron spin resonance signals of monomeric Chl(+.) ranging between 9.2 and 7.8 G in solution. These changes in electronic configuration and ease of oxidation are attributed to mixing of two nearly degenerate ground states of the radicals theoretically predicted by molecular orbital calculations. Comparison of the properties of chlorophyll in vitro with the optical, redox, and magnetic characteristics attributed to P-680, the primary donor of photosystem II which mediates oxygen evolution in plant photosynthesis, leads us to suggest that P-680 may be a ligated chlorophyll monomer whose function as a phototrap is determined by interactions with its (protein?) environment.
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Affiliation(s)
- M S Davis
- Department of Energy and Environment, Brookhaven National Laboratory, Upton, New York 11973
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Oxidation-reduction potential dependence of the flash-induced 518 nm absorbance change in chloroplasts. FEBS Lett 2001. [DOI: 10.1016/0014-5793(78)80362-7] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Knaff DB. The effect of pH on the midpoint oxidation-reduction potentials of components associated with plant photosystem II. FEBS Lett 2001. [DOI: 10.1016/0014-5793(75)80742-3] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Datta SN, Parandekar PV, Lochan RC. Identity of Green Plant Reaction Centers from Quantum Chemical Determination of Redox Potentials of Special Pairs. J Phys Chem B 2001. [DOI: 10.1021/jp001139z] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Sambhu N. Datta
- Department of Chemistry, Indian Institute of Technology - Bombay, Powai, Mumbai - 400 076, India
| | - Priya V. Parandekar
- Department of Chemistry, Indian Institute of Technology - Bombay, Powai, Mumbai - 400 076, India
| | - Rohini C. Lochan
- Department of Chemistry, Indian Institute of Technology - Bombay, Powai, Mumbai - 400 076, India
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Tanaka K, Tanaka S. Redox Potential of Fe4S4Cluster in Hydrophobic and Hydrophilic Spheres. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 1991. [DOI: 10.1246/bcsj.64.1192] [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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Golbeck JH. Structure, function and organization of the Photosystem I reaction center complex. BIOCHIMICA ET BIOPHYSICA ACTA 1987; 895:167-204. [PMID: 3333014 DOI: 10.1016/s0304-4173(87)80002-2] [Citation(s) in RCA: 177] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- J H Golbeck
- Department of Chemistry, Portland State University, OR 97207
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Rutherford AW, Heathcote P. Primary photochemistry in photosystem-I. PHOTOSYNTHESIS RESEARCH 1985; 6:295-316. [PMID: 24442951 DOI: 10.1007/bf00054105] [Citation(s) in RCA: 81] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/1984] [Accepted: 01/31/1985] [Indexed: 06/03/2023]
Abstract
In this review, the main research developments that have led to the current simplified picture of photosystem I are presented. This is followed by a discussion of some conflicting reports and unresolved questions in the literature. The following points are made: (1) the evidence is contradictory on whether P700, the primary donor, is a monomer or dimer of chlorophyll although at this time the balacnce of the evidence points towards a monomeric structure for P700 when in the triplet state; (2) there is little evidence that the iron sulfur centers FA and FB act in series as tertiary acceptors and it is as likely that they act in parallel under physiological conditions; (3) a role for FX, probably another iron sulfur centrer, as an obligatory electron carrier in forward electron transfer has not been proven. Some evidence indicates that its reduction could represent a pathway different to that involving FA and FB; (4) the decay of the acceptor 'A2 (-)' as defined by optical spectroscopy corresponds with 700(+) % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOramaaBa% aaleaadaqdaaqaaiaadIfaaaaabeaaaaa!37D1!\[F_{\overline X } \] recombination under some circumstances but under other conditions it probably corresponds with P700(+) A1 (-) recombination; (5) P700(+) A1 (-) recombination as originally observed by optical spectroscopy is probably due to the decay of the P700 triplet state; (6) the acceptor A1 (-) as defined by EPR may be a special semiquinone molecule; (7) A0 is probably a chlorophyll a molecule which acts as the primary acceptor. Recombination of P700(+) A0 (-) gives rise to the P700 triplet state.A working model for electron transfer in photosystem I is presented, its general features are discussed and comparisons with other photosystems are made.
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Affiliation(s)
- A W Rutherford
- Service de Biophysique, Department de Biologie, CEN Saclay, BP2, 91190, Gif sur Yvette, France
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Fry I, Robinson AE, Spath S, Packer L. The role of Na2S in anoxygenic photosynthesis and H2 production in the cyanobacterium Nostoc muscorum. Biochem Biophys Res Commun 1984; 123:1138-43. [PMID: 6091649 DOI: 10.1016/s0006-291x(84)80251-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Na2S is known to support anoxygenic photosynthesis in some strains of cyanobacteria and to stimulate H2 production in N2 fixing filaments of Nostoc muscorum. We have shown electron transfer between Na2S and Photosystem I to be dependent on cytochrome b559 which was detected only in vegetative cells. An electron mediator was required to support Na2S driven nitrogenase activity in isolated heterocysts. Na2S was also found to deplete the ATP pool, probably by inhibiting electron transfer from Photosystem I.
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Richter ML, Homann PH. Surface-charge related actions of polylysine on thylakoid membranes. Arch Biochem Biophys 1983; 222:67-77. [PMID: 6838230 DOI: 10.1016/0003-9861(83)90503-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Polycation binding to the negatively charged surface of chloroplast thylakoid membranes is known to cause an inhibition of photosystem I activity. It also interferes with the cation-dependent rearrangement of chlorophyll proteins in the thylakoid membrane. It was shown that added anions prevented or reversed the inhibition of photosystem I by polylysine without decreasing its binding to the membranes. Anions also caused a change in the interaction of the chlorophyll proteins in polylysine-treated thylakoids as indicated by an increase in the relative fluorescence intensity from photosystem II. In both cases, the relative effectiveness of the anions tested depended on their valence; for example, the tetravalent species Fe(CN)4-(6) was effective at concentration at least 2 orders of magnitude lower than the divalent species SO2-(4). These results suggest that anions act by screening the positive charge of the polylysine-coated membrane surface. Measurements of the response of the anionic fluorescent probe 1-anilinonapthalene-8-sulfonate to an addition of anions to polylysine-treated thylakoids supported this contention. It was concluded that the action of polylysine on photosystem I and on the chlorophyll proteins is mediated by changes of the electrical properties of the thylakoid membrane and may not involve a direct binding of the polycation to the affected membrane proteins.
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Peters FA, Van Wielink JE, Wong Fong Sang HW, De Vries S, Kraayenhof R. Studies on well coupled Photosystem I-enriched subchloroplast vesicles. Content and redox properties of electron-transfer components. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1983. [DOI: 10.1016/0005-2728(83)90062-2] [Citation(s) in RCA: 32] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Olsen LF. Transient kinetics of the electron transfer between P-700, plastocyanin and cytochrome f in chloroplasts suspended in fluid media at sub-zero temperatures. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1982. [DOI: 10.1016/0005-2728(82)90064-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Fultz ML, Durst RA. Mediator compounds for the electrochemical study of biological redox systems: a compilation. Anal Chim Acta 1982. [DOI: 10.1016/s0003-2670(01)95447-9] [Citation(s) in RCA: 155] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Photooxidation of the Reaction Center Chlorophylls and Structural Properties of Photosynthetic Reaction Centers. ACTA ACUST UNITED AC 1982. [DOI: 10.1007/978-3-642-81795-3_4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/26/2023]
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17
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Setif P, Mathis P. The oxidation-reduction potential of P-700 in chloroplast lamellae and subchloroplast particles. Arch Biochem Biophys 1980; 204:477-85. [PMID: 7447457 DOI: 10.1016/0003-9861(80)90059-4] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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18
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Jursinic P. POLAROGRAPHIC DETECTION OF AN ENDOGENOUS REDUCTANT GENERATED DURING FLASH ILLUMINATION OF CHLOROPLASTS. Photochem Photobiol 1980. [DOI: 10.1111/j.1751-1097.1980.tb03986.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Rich PR, Bendall DS. The redox potentials of the b-type cytochromes of higher plant chloroplasts. BIOCHIMICA ET BIOPHYSICA ACTA 1980; 591:153-61. [PMID: 7388012 DOI: 10.1016/0005-2728(80)90229-7] [Citation(s) in RCA: 87] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
1. In fresh chloroplasts,three b-type cytochromes exist. These are b-559HP (lambda max, 559 nm; Em at pH 7, +370 mV; pH-independent Em), b-559LP (lambda max, 559 nm; Em at pH 7, +20 mV; pH-independent Em) and b-563 (lambda max, 563 nm; Em at pH 7, -110 mV; pH-independent Em), b-559HP may be converted to a lower potential form (lambda max, 559 nm; Em at pH 7, +110 mV; pH-independent Em). 2. In catalytically active b-f particle preparations, three cytochromes exist. These are cytochrome f (lambda max, 554 nm; Em at pH 7, +375 mV, pK on oxidised cytochrome at pH 9), b-563 (lambda max, 563 nm; Em at pH 7, -90 mV, small pH-dependence of Em) and a b-559 species (lambda max, 559 nm, Em at pH 7, +85 mV; pH-independent Em). 3. A positive method of demonstration and estimation of b-559LP in fresh chloroplasts is described which involves the use of menadiol as a selective reductant of b-559LP.
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[25] P700 detection. Methods Enzymol 1980. [DOI: 10.1016/s0076-6879(80)69027-2] [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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Heber U, Kirk MR, Boardman NK. Photoreactions of Cytochrome b-559 and cyclic electron flow in photosystem II of intact chloroplasts. BIOCHIMICA ET BIOPHYSICA ACTA 1979; 546:292-306. [PMID: 444498 DOI: 10.1016/0005-2728(79)90047-1] [Citation(s) in RCA: 91] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The high potential cytochrome b-559 of intact spinach chloroplasts was photooxidized by red light with a high quantum efficiency and by far-red light with a very low quantum efficiency, when electron flow from water to Photosystem II was inhibited by a carbonyl cyanide phenylhydrazone (FCCP or CCP). Dithiothreitol, which reacts with FCCP or CCCP, reversed the photooxidation of cytochrome b-559 and restored the capability of the chloroplasts to photoreduce CO2 showing that the FCCP/CCCP effects were reversible. The quantum efficiency of cytochrome b-559 photooxidation by red or far-red light in the presence of FCCP was increased by 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone which blocks oxidation of reduced plastoquinone by Photosystem I. When the inhibition of water oxidation by FCCP or CCP was decreased by increased light intensities, previously photooxidized cytochrome b-559 was reduced. Red light was much more effective in photoreducing oxidized high potential cytochrome b-559 than far-red light. The red/far-red antagonism in the redox state of cytochrome b-559 is a consequence of the different sensitivity of the cytochrome to red and far-red light and does not indicate that the cytochrome is in the main path of electrons from water to NADP. Rather, cytochrome b-559 acts as a carrier of electrons in a cyclic path around Photosystem II. The redox state of the cytochrome was shifted to the oxidized side when electron transport from water became rate-limiting, while oxidation of water and reduction of plastoquinone resulted in its shifting to the reduced side.
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Rickard LH, Landrum H, Hawkridge F. 261 - A Mediated Electrochemical Redox Study of Soluble Spinach Ferredoxin Using Optically Coupled Methods. ACTA ACUST UNITED AC 1978. [DOI: 10.1016/0302-4598(78)80008-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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25
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Knaff DB. The role of cytochrome b6 and cytochrome f in cyclic electron flow in a blue-green alga. Arch Biochem Biophys 1977; 182:540-5. [PMID: 409351 DOI: 10.1016/0003-9861(77)90535-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Wood PM, Bendall DS. The reduction of plastocyanin by plastoquinol-1 in the presence of chloroplasts. A dark electron transfer reaction involving components between the two photosystems. EUROPEAN JOURNAL OF BIOCHEMISTRY 1976; 61:337-44. [PMID: 174911 DOI: 10.1111/j.1432-1033.1976.tb10027.x] [Citation(s) in RCA: 84] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The reduction of plastocyanin by plastoquinol-1 was efficiently catalysed by disrupted chloroplasts or etioplasts in the dark. The reaction was inhibited by 2,5-dibromomethylisopropyl-p-benzo-quinone which inhibits photosynthetic electron transport between plastoquinone and cytochrome f. Evidence is presented that the reduction took place via cytochrome f, and that plastoquinone-9 was not involved. Triton X-100 and organic solvents were inhibitory, but partial fractionation was achieved without loss of activity by density gradient centrifugation in the presence of high digitonin concentrations. All active material contained cytochromes b-559LP and b-563 in addition to cytochrome f, but these b-type cytochromes were not directly involved. Other 1-electron acceptors could be used in place of plastocyanin, for instance ferricyanide and Pseudomonas cytochrome c-551. The reaction can be applied to give a sensitive dark assay for active cytochrome f. It is suggested that cytochrome f possesses two sites for interaction with redox reagents: a hydrophilic site with which plastocyanin reacts by electron transfer and a hydrophobic site with which plastoquinol reacts by hydrogen atom transfer.
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Ke B, Sugahara K, Shaw ER. Further purification of "Triton subchloroplast fraction I" (TSF-I particles). Isolation of a cytochrome-free high-P-700 particle and a complex containing cytochromes f and b6, plastocyanin and iron-sulfur protein(s). BIOCHIMICA ET BIOPHYSICA ACTA 1975; 408:12-25. [PMID: 169916 DOI: 10.1016/0005-2728(75)90154-1] [Citation(s) in RCA: 42] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The "Triton Subchloroplast Fraction I" or "TSF-I particles" can be further fractionated into a cytochrome fraction and a P-700-containing fraction essentially free of cytochromes. The cytochrome complex contains cytochromes f and b6 in approx. equimolar amounts, and, in addition, also plastocyanin and one iron-sulfur protein, all in the bound state. Bound plastocyanin was characterized by EPR spectroscopy. The EPR spectrum of the bound iron-sulfur protein resembles that previously detected in Phostosystem I particles under highly reducing conditions at lower than -560 mV. The redox potential of P-700 in the cytochrome-free high-P-700 particles was measured to be +468 mV; those of cytochromes f and b6 are +345 and -140 mV, respectively. Among the four components present in the complex, only cytochrome f can be coupled to a Photosystem I particle and undergoes photooxidation. This coupled photooxidation is totoally inhibited by KCN and only partially inhibited by HgCl2. The similarity of the complex containing cytochromes f and b6, plastocyanin, and an iron-sulfur protein to complexes III and IV of the mitochondrial respiratory redox chain and a possible involvement of the complex in cyclic photophosphorylation are noted and discussed.
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Cox RP. The properties of cytochrome f and P700 in chloroplasts suspended in fluid media at sub-zero temperatures. EUROPEAN JOURNAL OF BIOCHEMISTRY 1975; 55:625-31. [PMID: 1175616 DOI: 10.1111/j.1432-1033.1975.tb02200.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
1. The properties of P700 and cytochrome f have been studied at sub-zero temperatures in chloroplasts suspended in a medium containing 50% (v/v) ethylene glycol. The dark reduction of these components after a period of illumination provided information about the rate-limiting step of photosynthetic electron transport under these conditions. 2. The oxidation of P700 on illumination in the presence of methyl viologen and its subsequent dark reduction can be observed at -35 degrees C. This cycle of reactions could be repeated many times. The rate of reduction was increased by NH4Cl and reduction was inhibited by 3(3,4-dichlorophenyl)-1,1-dimethylurea. 3. The oxidation and reduction of cytochrome f could also be observed under similar conditions. The activation energies for the reduction of cytochrome f and P700 are similar (about 75 kJ mol-1) and the reduction of cytochrome f is also inhibited by dichlorophenyldimethylurea and stimulated by NH4Cl. 4. The reduction of both cytochrome f and P700 seemed to follow first-order kinetics, but the t1/2 for the redcution of the cytochrome was at least three times that for the reduction of P700 at the same temperature. It was concluded that the results were only compatible with a model in which the main pathway of electrons from plastoquinone to P700 involved cytochrome f if the equilibrium constant between the cytochrome and P700 was very much less than that expected from their redox potentials.
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Wood PM, Bendall DS. The kinetics and specificity of electron transfer from cytochromes and copper proteins to P700. BIOCHIMICA ET BIOPHYSICA ACTA 1975; 387:115-28. [PMID: 1125282 DOI: 10.1016/0005-2728(75)90056-0] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The rates of electron transfer to P700 from plastocyanin and cytochrome f have been compared with those from three other c-type cytochromes and azurin, a copper protein resembling plastocyanin. Three different disruptive techniques were used to expose P700; digitonin, Triton X-100 and sonication. The following rate constants were measured at 25 degrees C, pH 7.0, with digitonin-treated chloroplasts: plastocyanin, 8 x 10(7)M(-1) x s(-1); red-algal cytochrome c-553, 1.9 x 10(7)M(-1) x s (-1); Pseudomonas cytochrome c-551, 8 x 10(6)M(-1) x s (-1); azurin, less than or = 3 x 10(5)M(-1) x s (-1); cytochrome f, less than or = 2 x 10(4)M(-1) x s (-1); mammalian cytochrome c, less than or = 2 x 10(4)M(-1) x s (-1). For electron transfer from plastocyanin, the effects of ionic strength, pH and temperature were also studied, and saturation effects found in earlier work were avoided by a full consideration of the various secondary reactions and inclusion of superoxide dismutase. The relative rates are discussed in relation to photosynthetic electron transport.
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Maroc J, Garnier J. [Cytochrome b-559 photooxidation in the presence of carbonyl cyanide p-trifluorometh-oxyphenylhydrazone and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone or p-benzoquinone in three non-photosynthetic mutants of Chlamydomonas reinhardti (author's transl)]. BIOCHIMICA ET BIOPHYSICA ACTA 1975; 387:52-68. [PMID: 1125287 DOI: 10.1016/0005-2728(75)90051-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Studies of absorbance related to the cytochrome b-559 photooxidation induced by FCCP, with and without addition of 3-p-chlorophenyl-1, 1-dimethylurea (CMU), DBMIB or p-benzoquinone, in whole cells and in chloroplast fragments of Chlamydomonas reinhardti, were carried out. In addition to the wild type, three strains of non-photosynthetic mutants were used: Fl 5, which lacks P 700; Fl 9 and Fl 15, which are deficient in bound cytochrome c-553 and in cytochrome b-563. In the presence of FCCP, whole cells and chloroplast fragments of the four strains showed a System II-dependent photooxidation of cytochrome b-559. This photooxidation was inhibited by CMU but it occurred again in presence of FCCP, CMU and DBMIB. In chloroplast fragments, cytochrome b-559 photooxidation was also inhibited by an excess of FCCP; it was recovered, likewise, by addition of DBMIB. In whole cells, the highest measured redox changes were: 1 mu mol oxidized cytochrome b-559 per 1 mmol chlorophyll, corresponding approximately to about one seventh (wild type, Fl5) or one fifth (Fl 9, Fl 15) of the total amount of this cytochrome. Another kind of cytochrome b-559 photooxidation, CMU-insensitive, also occurred in the mutants Fl 9 and Fl 15 and in the wild type, but not in the mutant Fl 5. This latter kind of photooxidation was observed with chloroplast fragments in the presence of FCCP and CMU and also with whole cells in the presence of FCCP, CMU and p-benzoquinone. These reactions can be attributed to the Photosystem I; they do not require the intervention of the cytochrome c-553. A high-potential form of cytochrome b-559, hydroquinone-reducible, was involved in these two kinds of photooxidation. In addition, a lower potential form, reducible only by ascorbate, appeared to be able to interfere also. An interpretation is attempted, taking into consideration the various effects of FCCP and DBMIB, at different concentrations, on photosynthetic electron transport.
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Knaff DB, Buchanan BB. Cytochrome b and photosynthetic sulfur bacteria. BIOCHIMICA ET BIOPHYSICA ACTA 1975; 376:549-60. [PMID: 1125222 DOI: 10.1016/0005-2728(75)90174-7] [Citation(s) in RCA: 64] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Chromatophores isolated from the purple sulfur bacterium Chromatium and the green sulfur bacterium Chlorobium exhibit absorbance changes in the cytochrome alpha-band region consistent with the presence of a b-type cytochrome. Cytochrome content determined by reduced minus oxidized difference spectra and by heme photochemically active bacteriochlorophyll (reaction-center bacteriochlorophyll). The b-type cytochrome in Chromatium has an alpha-band maximum at 560 nm and a midpoint oxidation-reduction potential of -5 mV at pH 8.0. The b-type cytochrome in Chlorobium has an alpha-band maximum at 564 nm and an apparent midpoint oxidation-reduction potential near -90 mV. Chromatophores isolated from both Chromatium and Chlorobium cells catalyze a photoreduction of cytochrome b that is enhanced in the presence of antimycin A. Antimycin A and 2-n-heptyl-4-hydroxyquinoline-N-oxide inhibit endogenous (but not phenazine methosulfate-mediated) cyclic photophosphorylation in Chromatium chromatophores and non-cyclic electron flow from Na-2S to NADP in Chlorobium chromatophores. These observations suggest that b-type cytochromes may function in electron transport reactions in photosynthetic sulfur bacteria.
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Knaff DB. The effect of o-phenanthroline on the midpoint potential of the primary electron acceptor of photosystem II. BIOCHIMICA ET BIOPHYSICA ACTA 1975; 376:583-7. [PMID: 235986 DOI: 10.1016/0005-2728(75)90180-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The primary electron acceptor of Photosystem II has a midpoint oxidation-reduction potential of +95 mV at pH 7.0 in Photosystem II chloroplast fragments prepared by digitonin treatment. The midpoint potential of the acceptor has a pH dependence of -60 mV/pH unit. At concentrations that inhibit oxygen evolution, o-phenanthroline shifts the midpoint potential of the primary acceptor by +70 mV. The shifted potential retains the same dependence on pH. The effect of o-phenanthroline suggests that it interacts directly with the primary electron acceptor of photosystem II in a manner similar to that reported previously for the primary electron acceptor in purple photosynthetic bacteria.
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Wood PM. Rate of electron transfer between plastocyanin, cytochrome f, related proteins and artificial redox reagents in solution. BIOCHIMICA ET BIOPHYSICA ACTA 1974; 357:370-9. [PMID: 4472275 DOI: 10.1016/0005-2728(74)90027-9] [Citation(s) in RCA: 70] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Aparicio PJ, Ando K, Arnon DI. Photochemical activity and components of membrane preparations from blue-green algae. II. Low-temperature photooxidation of cytochrome b559. BIOCHIMICA ET BIOPHYSICA ACTA 1974; 357:246-51. [PMID: 4214171 DOI: 10.1016/0005-2728(74)90064-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Abstract
Photosynthesis begins with the absorption of light energy and this absorbed energy is transferred to special sites, termed reaction centres. At these sites, the light energy is transformed into chemical products through an oxidation-reduction reaction that generates the primary reactants, an oxidized pigment molecule (P+) and a reduced electron acceptor (A–) (Clayton, 1972). The subsequent reactions of these species in the dark ultimately results in the formation of chemical products required for the fixation of CO2. In this essay we will discuss the nature of the primary reactants generated in the light reactions of chloroplast photosynthesis, stressing recent advances in the identification and characterization of such reactants.
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