Photophosphorylation In Vivo

Simonis, W.; Urbach, W.

doi:10.1146/annurev.pp.24.060173.000513

Cited by 109 publications

(36 citation statements)

References 140 publications

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“…2 Regulation of Cyclic Photophosphorylation. The ATP photochemically generated by cyclic photophosphorylation may be used not only for CO2 assimilation but also for other ATP-requiring cellular activities (11). One example of such "nonphotosynthetic" use of ATP derived from cyclic photophosphorylation is amino acid incorporation by isolated chloroplasts (46 is curtailed or stopped altogether because of the well-known midday closure of stomata in leaves (47,48).…”

Section: Resultsmentioning

confidence: 99%

Regulation of ferredoxin-catalyzed photosynthetic phosphorylations.

Arnon¹,

Chain²

1975

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

134

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Under aerobic conditions that are likely to prevail in chloroplasts in vivo, the optimal concentration of ferredoxin for cyclic photophosphorylation was found to be equal to that required for NADP reduction and about onetenth of that needed for cyclic photophosphorylation under anaerobic conditions. In the presence of ferredoxin and NADP, cyclic photophosphorylation operated concurrently with noncyclic photophosphorylation, producing an ATP: NADPH ratio of about 1.5. The effective operation of ferredoxin-catalyzed cyclic photophosphorylation by itself required a curtailment of the electron flow from water which was accomplished experimentally by the use of either an inhibitor or far-red monochromatic light. An unexpected discovery was that the operation of cyclic photophosphorylation by itself was also regulated by a back reaction of NADPH and ferredoxin with two components of chloroplast membranes, component C550 and cytochrome b559. The significance of these findings to photosynthesis in vivo is discussed.Solar energy is first converted into biologically useful chemical energy by photosynthetic phosphorylation (photophosphorylation), the process by which the photosynthetic apparatus transforms the electromagnetic energy of sunlight into phosphate bond energy of ATP, the universal energy carrier of living cells. The energy of the photochemically generated ATP and reducing power is conserved through the biosynthesis of organic compounds from CO2. When these are later degraded by fermentation and respiration, reducing power and ATP are regenerated to drive the multitude of endergonic reactions and activities of living cells.Chloroplasts, the photosynthetic organelles of green plants, have two types of photophosphorylation, cyclic and noncyclic, names devised to denote the coupling of ATP formation to a light-induced electron flow that is either of a closed (cyclic) type that yields only ATP or of a unidirectional (noncyclic) type that yields not only ATP but also NADPH as reducing power (1). Ferredoxin plays a key role in both. In cyclic photophosphorylation ferredoxin is the endogenous catalyst (2, 3) and in noncyclic photophosphorylation ferredoxin is the electron acceptor (4) that in turn reduces NADP by an enzymatic reaction that is independent of light (5).In this paper we report the concurrent operation of ferredoxin-dependent cyclic and noncyclic photophosphorylation under conditions that are likely to exist in chloroplasts in vivo. These experiments led to the discovery that noncyclic electron flow provides a regulatory mechanism that permits cyclic photophosphorylation to operate either concurrently with the noncyclic type (and thereby to increase the ratio of ATP to NADPH as needed for photosynthetic CO2 assimilation) or to operate by itself and produce only ATP for those endergonic reactions that do not require photochemically generated reducing power. Illumination. Incident monochromatic illumination was provided by a 250 W tungsten-halogen lamp (General Electric type EHN) and appropriate inte...

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Section: Resultsmentioning

confidence: 99%

Regulation of ferredoxin-catalyzed photosynthetic phosphorylations.

Arnon¹,

Chain²

1975

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

134

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“…Based upon experiments with isolated Class 1 chloroplasts, Forti and Rosa [5] reported that DBMIB had no effect on the endogenous cyclic photophosphorylation. The endogenous cyclic pathway is often construed to be representative of the pathway in vivo [1]. This anomaly, and that on the kinetics of cytochrome freduction reported by B6hme and Cramer [ 1 I] illustrate the major differences between investigations with higher plant chloroplasts and those with intact algae on this particular problem.…”

Section: Resultsmentioning

confidence: 99%

The role of plastoquinone in the in vivo photosynthetic cyclic electron transport pathway in algae

Biggins

1974

FEBS Letters

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“…Figure 7 shows that, at saturating C02, cyclic photophosphorylation contributes ATP to photosynthesis from very low to saturating light intensities. On the other hand, Heber et aL (14) concluded that cyclic photophosphorylation was involved mainly at moderate and high light intensities, whereas the evidence in the reviews of Simonis and Urbach (24) and Gimmler (1 1) indicated that cyclic photophosphorylation was saturated at low light intensities. The reasons for these discrepancies are not known, but might be partly related to the different experimental conditions used.…”

Section: Discussionmentioning

confidence: 99%

“…The reasons for these discrepancies are not known, but might be partly related to the different experimental conditions used. For example, red light was used in the experiments of Heber et al (14) while the uptake of phosphate had been used as an indicator reaction in the evidence discussed by Simonis and Urbach (24) and Gimmler (1 1). The reported stimulation of photosynthesis in chloroplasts by antimycin A under anaerobic and aerobic conditions (19,22,25,28) indicates the complex nature of the direct and indirect effect of antimycin A on photosynthetic carbon metabolism.…”

Section: Discussionmentioning

confidence: 99%

Evidence for Cyclic Photophosphorylation during ¹⁴CO₂ Fixation in Intact Chloroplasts

Woo¹

1983

Plant Physiol.

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This study examines the effect of antimycin A and nitrite on 14CO2 fixation in intact chloroplasts isolated from spinach (Spiucia oeracea L.) leaves. Antimycin A (2 micromolar) strongly inhibited CO2 fixation but did not appear to inhibit or uncouple linear electron transport in intact chloroplasts. The addition of small quantities (40-100 micromolar) of nitrite A stoichiometric balance of ATP/NADPH in the chloroplast is essential for optimum photosynthesis. It is now widely accepted that such a stoichiometric balance of ATP/NADPH could not be achieved by linear electron transport from H20 to NADP+ alone (1 1). Assuming that the ATP/NADPH ratio generated via linear electron transport is 1.33, the extra ATP needed would presumably be derived from cyclic and/or pseudocyclic electron transport.High rates of 02 uptake have been measured in thylakoid preparations from spinach leaves in the presence of high concentrations of Fd (1; R. T. Furbank and M. R. Badger, unpublished), during photosynthesis in intact chloroplasts and cells (8,9), and in leaves of C3 plants (6,10). The values of 02 uptake measured in these studies are comparable to and, in several cases, exceeded the value (1 1.3% of total 02 evolution) required for the generation of all the extra ATP needed for CO2 fixation. This evidence suggests that pseudocyclic electron transport plays a significant (dominant) role in the ATP/NADPH balance during photosynthesis. Marsho et al. (18) found that, although there was a significant rate of 02 uptake in intact chloroplasts during the lag phase of photosynthesis, this diminished to a relatively insignificant level during steady-state photosynthesis. These low rates of 02 uptake were relatively insensitive to increases in light intensity which greatly stimulated photosynthesis (14). These and a number of other workers (3,4,20,23,32) have provided evidence for cyclic flow during photosynthesis in thylakoids, chloroplasts, and intact leaves. Quantitative measurements of Cyt turnover in intact chloroplasts (26) have also indicated substantial cyclic flow. But the corresponding rates of 02 evolution during these measurements were low. Thus, the relative contribution of cyclic versus pseudocyclic flow to the ATP/NADPH balance during photosynthesis remains unresolved. Furthermore, the reasons for the discrepancies between high (8, 9) and low (14, 18) rates of 02 uptake measured during photosynthesis in chloroplasts and cells remain to be resolved.In thylakoids, antimycin A is a reported potent inhibitor of Fddependent cyclic flow (2) but may function as an uncoupler at higher concentrations (7). In intact chloroplasts, antimycin A stimulated CO2 fixation under anaerobic conditions (19,22,25) and in aerobic conditions which were suboptimal (e.g. high Pi concentration) for CO2 fixation (28). But under aerobic conditions at optimal Pi, antimycin A strongly inhibited photosynthetic CO2 fixation in intact chloroplasts with concomitant decreases in energy-dependent processes such as Chl a fluorescence, 9-aminoacridin...

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Photophosphorylation In Vivo

Cited by 109 publications

References 140 publications

Regulation of ferredoxin-catalyzed photosynthetic phosphorylations.

Regulation of ferredoxin-catalyzed photosynthetic phosphorylations.

The role of plastoquinone in the in vivo photosynthetic cyclic electron transport pathway in algae

Evidence for Cyclic Photophosphorylation during ¹⁴CO₂ Fixation in Intact Chloroplasts

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Photophosphorylation In Vivo

Cited by 109 publications

References 140 publications

Regulation of ferredoxin-catalyzed photosynthetic phosphorylations.

Regulation of ferredoxin-catalyzed photosynthetic phosphorylations.

The role of plastoquinone in the in vivo photosynthetic cyclic electron transport pathway in algae

Evidence for Cyclic Photophosphorylation during 14CO2 Fixation in Intact Chloroplasts

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Evidence for Cyclic Photophosphorylation during ¹⁴CO₂ Fixation in Intact Chloroplasts