Duroquinol as an electron donor for chloroplast electron transfer reactions

White, Craig C.; Chain, Richard K.; Malkin, Richard

doi:10.1016/0005-2728(78)90137-8

Cited by 72 publications

(18 citation statements)

References 23 publications

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“…PSII was blocked by DCMU and electrons were donated by DQH2 as an analog to plastoquinol (15,28), the violaxanthin availability was restored to the control level (Figs. 4 and SA), although the enzymatic rate constant was still inhibited.…”

Section: Discussionmentioning

confidence: 99%

Inhibition of Violaxanthin Deepoxidation by Ultraviolet-B Radiation in Isolated Chloroplasts and Intact Leaves

Pfündel

Pan²,

Dilley³

1992

Plant Physiol.

111

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The effect of pretreatment with ultraviolet-B (UV-B) light (280-320 nanometers) on the enzymatic conversion of the diepoxyxanthophyll violaxanthin to the epoxy-free zeaxanthin occurring in thylakoid membranes was investigated. When isolated chloroplasts of pea (Pisum sativum) were exposed to UV-B, a biologically effective fluence of 7000 joules per square meter caused about 50% inhibition of the activity of the violaxanthin deepoxidase, measured as the first order rate constant of the absorbance change at 505 nanometers. The dose requirement for the inhibition of the deepoxidase in intact leaves, however, was about 2 orders of magnitude higher. The inhibition of the rate constant was observed for both the dark deepoxidation at pH 5, and for the light-driven deepoxidation induced by the lumen acidification due to electron transport from H20 to methylviologen or due to a photosystem I partial reaction with duroquinol as the electron donor. The availability of violaxanthin was not directly affected by UV-B radiation, as shown for UV-B-treated chloroplasts by the final extent of the 505 nanometer change measured in the dark at pH 5 or by the partial photosystem I reaction. A significant decrease in the violaxanthin availability was observed when lumen acidification was caused by electron transport from H20 to methylviologen. That effect was probably caused by the wellknown UV-B inhibition of photosystem 11 with a subsequent decreased ability to reduce the plastoquinone pool, the redox state of which is believed to regulate the final amount of converted violaxanthin.

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Section: Discussionmentioning

confidence: 99%

Inhibition of Violaxanthin Deepoxidation by Ultraviolet-B Radiation in Isolated Chloroplasts and Intact Leaves

Pfündel

Pan²,

Dilley³

1992

Plant Physiol.

111

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“…Possibly, a rapid phase in the reduction of cytochrome f is masked by a simultaneous reoxidation by its electron acceptor, plastocyanin. The relation between cytochrome f and plastocyanin is not well understood (3); their respective redox states correlate poorly (10,13,26,27). Alternatively, a might be a plastocyanin, or the "Rieske" iron-sulfur center (27).…”

Section: Discussionmentioning

confidence: 99%

Electron flow through plastoquinone and cytochromes b6 and f in chloroplasts.

Velthuys¹

1979

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

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Communicated by Bessel Kok, March 26, 1979 ABSTRACT With dark-adapted chloroplasts in which the plastoquinone was oxidized, a partial reduction of cytochrome be was obtained upon illumination with a pair of short saturating flashes. The second flash of the pair was much more effective than the first, and the reduction was inhibited by the system II inhibitor diuron. When the plastoquinone pool was reduced, both the reduction and the oxidation of cytochrome be were accelerated. The cytochrome be oxidation appeared to proceed in association with the reduction of cytochrome f, although these cytochromes are not simply connected in series. From these observations it is inferred that electron flow to the secondary donors of system I alternately causes the reduction and the oxidation of cytochrome be. An interpretation is offered that also accounts for the transmembrane proton translocation that is associated with the oxidation of plastohydroquinone.

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“…DISCUSSION Duroquinone-dependent NAD(P)H oxidases appear to be ubiquitous in plant tissues (18). Duroquinone (2,3,5,6-tetramethylbenzoquinone) interacts in photosynthetic systems at the level of plastoquinone and, possibly, plastocyanin (26). It acts as an electron acceptor for respiratory chain dehydrogenases (23), and as a quinol it is a donor for mitochondrial ubiquinone and b-Cyt (2).…”

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confidence: 99%

Kinetic Characterization of Reduced Pyridine Nucleotide Dehydrogenases (Duroquinone-Dependent) in Cucurbita Microsomes

Pupillo¹,

Valenti²,

Luca³

et al. 1986

Plant Physiol.

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Some properties of microsomal electron transfer chains, dependent for oxidase activity on addition of NADH or NADPH, duroquinone, and oxygen (L. De Luca et al., 1984, Plant Sci Lett 36: 93-98) are described. Activity is characterized by negatively cooperative kinetics toward reduced pyridine nucleotides, with limiting K,, of 10 to 50 micromolar at pH 7.0 (increasing at lower pH), as well as toward duroquinone with limiting K, of 100 to 400 micromolar regardless of pH. Molecular oxygen is reduced by the enzyme complex with S_.s of about 30 micromolar and production of H20 and H202, without superoxide involvement. The ratio NAD(P)H:02 averages 1.35 in the presence of KCN and 1.85 in its absence. The pyridine nucleotide specificity of the dehydrogenases has been investigated by kinetic competition experiments. Some enzyme heterogeneity was established for all preparations. At least two enzymes are detectable in plasma membrane-enriched fractions: a major NAD(P)H dehydrogenase having an acid pH optimum, and an NADPH dehydrogenase active around neutrality. Addition of Triton X-100 strongly enhances the activity over most of the pH scale, but depresses it increasingly at pH values higher than 8.0, to the effect that pH profile shows, under these conditions, a major peak at about pH 5.8 for both NADH and NADPH oxidase. Results with endoplasmic reticulum preparations are similar, except that they suggest the presence of still more activities at and above pH 7. The results are interpreted in terms of different complexes catalyzing electron transfer from NAD(P)H to 02 without release of intermediates.Recent studies (1,3,7,21,22,25) indicate that reducing equivalents can be transferred from the inside of plant cells to the outer space through the plasma membrane, for control of the neighboring environment, uptake of nutrients, and intracellular regulation. An NADH oxidase ofroot cell surfaces, possibly coupled to a transport system (12,14), has been isolated and seems to contain quinone (15). Some typical redox chain components such as flavins and a light sensitive b-type Cyt are present in the plasmalemma (8,10,13,27 (16), and may not be related to the bulk of DQ-dependent oxidases of the plasma membrane.Because of the uncertainties, we have undertaken a detailed biochemical characterization of these oxidases. This paper deals mainly with the nature ofthe reactions. It also shows that among different components a pyridine nucleotide-nonspecific dehydrogenase is responsible for most of the activity.MATERIALS AND METHODS Plant Material and Tissue Fractionation (5, 9). Cucurbita pepo L. was grown from seeds (hybrid 'Senator', Asgrow Co.) for 5 d in the dark at 24°C on vermiculite. Hypocotyl segments 2 to 3 cm below the hook were harvested. All subsequent procedures were carried out on ice in daylight.Hypocotyl sections were chopped with razor blades in two volumes of extraction medium (0.25 M sucrose, 50 mM Tris-HCl pH 7.5, 1 mm Na2EDTA, 1 mm Na2EGTA), then ground in a mortar and squeezed through a nylon cloth. The...

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Duroquinol as an electron donor for chloroplast electron transfer reactions

Cited by 72 publications

References 23 publications

Inhibition of Violaxanthin Deepoxidation by Ultraviolet-B Radiation in Isolated Chloroplasts and Intact Leaves

Inhibition of Violaxanthin Deepoxidation by Ultraviolet-B Radiation in Isolated Chloroplasts and Intact Leaves

Electron flow through plastoquinone and cytochromes b6 and f in chloroplasts.

Kinetic Characterization of Reduced Pyridine Nucleotide Dehydrogenases (Duroquinone-Dependent) in Cucurbita Microsomes

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