Enhancement effects and the identity of the two photochemical reactions of photosynthesis.

McSwain, Berah D.; Arnon, Daniel I.

doi:10.1073/pnas.61.3.989

Cited by 60 publications

(20 citation statements)

References 29 publications

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“…The thylakoids consisted of osmotically disrupted chloroplasts that retained the capacity for complete noncyclic electron transport from water to ferredoxin/NADP+ and photosynthetic phosphorylation. Ferredoxin was isolated and purified by R. K. Chain, and photoreduction of NADP+ was measured as described (19). DBMIB was kindly supplied by A. Trebst (Ruhr Universitat, Bochum, F.R.G.…”

Section: Methodsmentioning

confidence: 99%

Cytochrome b -559 and proton conductance in oxygenic photosynthesis

Arnon

Tang

1988

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

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Although cytochrome b-559 has long been known as a membrane-bound redox component closely linked to the reaction center of the oxygen-generating photosystem (PSII), its role in photosynthesis has remained obscure. This paper reports evidence and outlines a hypothesis in support of a "b-559 cycle"-i.e., a light-induced, cytochrome b-559-dependent, cyclic electron transport pathway around PSU that promotes translocation of protons from plastoquinol into the aqueous domain (lumen) of photosynthetic membranes (thylakoids). Light-induced proton transport coupled to lightinduced electron transport is an essential aspect of energy transduction in photosynthesis because it generates an electrochemical proton gradient that drives ATP synthesis by the process of photosynthetic phosphorylation. The principal carrier of electrons and protons in thylakoids is the plastoquinone/plastoquinol couple. We propose that the b-559 cycle functions as a redox-linked proton pump that may operate jointly with the Rieske iron-sulfur pathway in oxidizing plastoquinol. The overall effect of such concerted oxidation of plastoquinol would be the translocation into the thylakoid lumen of two protons for each electron transferred from water to plastocyanin via plastoquinone.Light-induced proton transport, coupled to light-induced electron transport, gained prominence in photosynthesis research with the recognition that it produces in photosynthetic membranes (thylakoids) an electrochemical proton gradient (A/.tH+) that drives ATP synthesis (1) in the process of photosynthetic phosphorylation (2). This process consists of cyclic (anoxygenic) photophosphorylation in which ATP is the sole product and noncyclic (oxygenic) photophosphorylation in which ATP formation is accompanied by oxygen evolution and the generation ofreducing power whose carrier is ferredoxin (2, 3). Oxygen apart, ATP and reduced ferrodoxin are the two products of transduction of sunlight's electromagnetic energy into forms of chemical energy that, directly or through intermediates, drive the biosynthetic and regulatory reactions of photosynthesis including, but not limited to, CO2 assimilation (4).In noncyclic, oxygenic photophosphorylation, A/.H+ is generated by protons released from two sources: the photooxidation of water (see Discussion) and the oxidation of plastoquinol (PQH2). As for PQH2, the accepted view is that thylakoids can oxidize it only via the Rieske iron-sulfur center pathway that is sensitive to inhibition by dibromothymoquinone (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, DBMIB) (5, 6). However, evidence was recently obtained (7) that PQH2 is also photooxidized by an alternative, cyclic pathway not inhibited by DBMIB. The cyclic pathway was uncovered through the use of uncouplers, specifically proton conductors (protonophores). Two chemically diverse photonophores, 2,6-di-(t-butyl)-4-(2',2'-dicyanovinyl)phenol (SF 6847) (8,9) and carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP) (10, 11), induced oxidation of PQH2 and dramatically lowered...

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Section: Methodsmentioning

confidence: 99%

Cytochrome b -559 and proton conductance in oxygenic photosynthesis

Arnon

Tang

1988

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

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“…Chlorophyll concentrations were determined as described by Arnon (21). Light-induced NADP reduction, with either water or reduced dye (2,6-dichlorophenol indophenol) as electron donor, was measured as described (22). Samples to be illuminated were placed in epr tubes and small amounts of glucose and glucose oxidase were added.…”

Section: Methodsmentioning

confidence: 99%

Primary Reactions of Photosynthesis: Photoreduction of a Bound Chloroplast Ferredoxin at Low Temperature as Detected by EPR Spectroscopy

Malkin

Bearden

1971

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

166

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An electron paramagnetic resonance signal was observed at 250K in whole spinach chloroplasts after illumination at 770K. The light-induced epr spectrum had g-values (g& = 1.86, g, = 1.94, g. = 2.05) and a temperature dependence that were characteristic of the reduced state of a plant-type ferredoxin. The light-induced epr spectrum was also observed in broken spinach chloroplasts from which soluble ferredoxin was removed. Chemical analyses showed that both whole and broken spinach chloroplasts contained amounts of nonheme iron and "acid-labile sulfide" consistent with the presence of a bound iron-sulfur protein, at a level of about one molecule per 75 chlorophyll molecules. These results support the conclusion that chloroplasts contain a bound ferredoxin that may serve as a primary low-potential electron acceptor in photosynthesis.

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“…The initial rate of electron transport from H2O to NADP+ was measured spectro-photometrically in 0.2 mm (0.5 ml) cuvettes by recording the absorbance change at 340 nm in a Zeiss spectrophotometer, modified as described earlier (24,36). The actinic light (1000 w iodine lamp) was passed through two interference filters (Balzer's Calflex C and Balzer's wide band DT-red) and the intensity at the cuvette was 1.15 X IO 4 ergs-cm~2-sec~1.…”

Section: Methodsmentioning

confidence: 99%

Effect of linolenate on photosynthesis by intact spinach chloroplasts I. Inhibition of orthophosphate uptake and of 3-P-glyceraldehyde efflux across the chloroplast envelope

Siegenthaler

Akamba

1979

Plant and Cell Physiology

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Linolenic acid (Cis:3) inhibited photosynthesis by intact spinach chloroplasts. This inhibition was due neither to a lack of NADPH in chloroplasts nor to a direct inhibition of the enzyme activities in the Calvin-Benson cycle. Linolenate inhibited CO2 fixation and oxygen evolution more effectively than NADP+ photoreduction but did not inhibit the activity of several key enzymes of the Calvin cycle. Linolenate inhibited phosphate influx and 3-phosphoglyceraldehyde efflux across the chloroplast envelope. A hypothesis explaining the inhibition of photosynthesis by linolenate is presented. Key words: Chloroplasts -Linolenic acid treatment -3-P-glyceraldehyde effluxPhosphate uptake -Photosynthesis -Spinach -Transport.The release of fatty acids during aging processes in vitro has been demonstrated in several cells and organelles such as human erythrocytes (30), mitochondria (10) and chloroplasts (8,16,22,39,41). In chloroplasts, the main fatty acids released in the course of aging are Cis-unsaturated fatty acids (8,16,39), particularly linolenic acid; these acids are the most abundant in the thylakoid (8, 39) and envelope (21) membrane lipids. So far, the action of endogenous (31, 38,39) and exogenous (26,(35)(36)(37)(38) fatty acids has been mainly studied in relation to the photochemical reactions of the thylakoid. It has been shown that such unsaturated fatty acids inhibit electron flow in photosystems II and I and the associated photophosphorylation (35,37), light-induced shrinkage in chloroplasts (35), and the light-generated ZlpH across thyalkoid membranes in a sequential fashion (37). In addition, fatty acids modify the physicochemical properties of the thylakoid membrane in such a way that swelling occurs (27,34) and that the JpH is diminished and pHi increased, inducing a shift of the pH optimum of electron flow towards acidity (37)(38)(39).In order to elucidate further the control of photosynthetic activities by these fatty acids, we have now studied the action of linolenate on the photosynthetic apparatus at a higher level of structural integrity. The initial point of interest was: Would free fatty acids influence photosynthetic carbon metabolism in intact chloro-1 This work is part of a doctoral program which is carried out by L. Mv6 Akamba in this laboratory. 395

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Enhancement effects and the identity of the two photochemical reactions of photosynthesis.

Cited by 60 publications

References 29 publications

Cytochrome b -559 and proton conductance in oxygenic photosynthesis

Cytochrome b -559 and proton conductance in oxygenic photosynthesis

Primary Reactions of Photosynthesis: Photoreduction of a Bound Chloroplast Ferredoxin at Low Temperature as Detected by EPR Spectroscopy

Effect of linolenate on photosynthesis by intact spinach chloroplasts I. Inhibition of orthophosphate uptake and of 3-P-glyceraldehyde efflux across the chloroplast envelope

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