Evidence for a reluctant‐dependent oxidation of chloroplast cytochrome <i>b</i>‐563

Chain, Richard K.

doi:10.1016/0014-5793(82)80115-4

Cited by 21 publications

(6 citation statements)

References 20 publications

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“…Brief mention of the possible pathways of cyclic electron transfer and their regulation is in order, since our results show that the switching of electrons into one cycle or the other must depend the redox balance of the ferredoxin pool and the interphotosystem electron carriers. The antimycin-Asensitive pathway is consistent with current working models of electron flow through b6-f and b-c 1 complexes, in which cytochromes b mediate transmembrane electron transfer [16,21,[44][45][46]. During electron flow to ferredoxin/O 2, at least two fac-tors may favor this pathway.…”

Section: Discussionsupporting

confidence: 82%

“…During electron flow to ferredoxin/O 2, at least two fac-tors may favor this pathway. First, if plastosemiquinone is the oxidant for reduced cytochrome b-563 toward the outside of the membrane [16,17,47] the accumulation of reduced ferredoxin in the medium would favor the initial reduction of oxidized plastoquinone. Second, the reducing conditions present in the interphotosystem chain should promote the reduction of b-563 by plastosemiquinone [15,46,48].…”

Section: Discussionmentioning

confidence: 99%

“…Cytochrome b-563 has been regarded as the carrier mediating electron flow from reduced ferredoxin to plastoquinone, but this role is now thought to be unlikely, since b-563 is only slowly reduced by hydrophilic reductants, including ferredoxin [13,14]. In addition, plastosemiquinone has been implicated as both the oxidant and the reductant of cytochrome b-563 [15][16][17][18][19][20], which is more con-sistent with Q-cycle schemes in which b-563 mediates electron transfer across the thylakoid membrane. The evidence for this type of cyclic pathway has recently been reviewed [21].…”

Section: Introductionmentioning

confidence: 99%

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Evidence for two cyclic photophosphorylation reactions concurrent with ferredoxin-catalyzed non-cyclic electron transport

Hosler

Yocum

1985

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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Addition of ferredoxin to isolated spinach chloroplast thylakoid membranes reconstitutes phosphorylating electron transfer characterized by elevated P/O ratios (1.6). When oxygen is the terminal electron acceptor for reduced ferredoxin, the P/O value is lowered by antimycin A or low concentrations (I0/~M) of heparin (an anionic macromolecule), but not by inhibition of the activity of membrane-bound ferredoxin-NADP reductase. When NADP is present as the terminal electron acceptor for reduced ferredoxin, the elevated P/O value (again 1.6) is unaffected either by antimycin A or low concentrations (I0/~M) of heparin. When ferredoxin-catalyzed cyclic or Q-loop activity is sensitive to antimycin A, the ferredoxin pool and P-700 are both present in a largely reduced state. The opposite result is obtained for antimycin-A-insensitive activity in the presence of NADP. Our results show that conditions exist whereby ferredoxin-catalyzed cyclic electron transport is insensitive to a classical inhibitor of the cytochrome b function. We suggest that the antimycin-A-insensitive pathway of ferredoxin-catalyzed cyclic electron transport may involve the activity of ferredoxin-NADP reductase.

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Section: Discussionsupporting

confidence: 82%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Evidence for two cyclic photophosphorylation reactions concurrent with ferredoxin-catalyzed non-cyclic electron transport

Hosler

Yocum

1985

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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“…By competing primarily with plastoquinone or plastosemiquinone at the same site, DNP-INT could inhibit electron transfer between the quinone or semiquinone and cytochrome b-563. A model, shown in fig. 5, which describes the reactions of cyclic electron transfer, has ferredoxin and the components of the cytochrome b-563/f complex arranged in a 'Q-cycle' [32], similar to that in [23). Two unique features are proposed here:…”

Section: Discussionmentioning

confidence: 99%

Sites of cytochromeb‐563 reduction, and the mode of action of DNP‐INT and DBMIB in the chloroplast cytochromeb‐563/fcomplex

O’Keefe¹

1983

FEBS Letters

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When ferredoxin is the reductant of cytochrome b-563 in the chloroplast cytochrome b-563/f complex, the reaction rate varies with pH in a manner which permits identification of a plastoquinone/plastosemiquinone couple as an intermediate in the reaction. The requirement for the inhibitor, DNP-INT, in this reaction, suggests that there are two sites in the complex where plastosemiquinone can react with cytochrome(s) b-563. The ineffectiveness of DBMIB in promotion of ferredoxin-mediated cytochrome b-563 reduction has led to a model where DBMIB and DNP-INT inhibit different electron transfer steps at the same, or overlapping, sites in the complex.

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“…In addition to the measurement of phosphorylation, this cycle can be measured in a number of ways, including the reduction of the cytochromesfand b6, the electrochromic shift, and the slow rereduction of P-700 ÷ (Slovacek and Hind 1977, Crowther and Hind 1980, Crowther et al 1983, Leegood et al 1983, Rurainski et al 1982. The main issue within the context of this review is how reducing equivalents from ferredoxin are introduced into the cytochrome bf complex, since some schemes suggest participation of reduced ferredoxin or ferredoxin:NADP reductase at, or near, the Qc site of the cytochrome bf complex (Crowther and Hind 1980, Chain 1982, O'Keefe 1983, Hartung and Trebst 1985, whereas others have proposed a mechanism for the two electron reduction of plastoquinone by PSI, effectively providing additional plastoquinol for the cytochrome bf complex (Hosler andYocum 1984, Moss andBendall 1984). Although not recognized as integral components of the cytochrome bf complex, the participation of other, as yet poorly characterized components which interact with cytochrome b6 during cyclic electron transfer, such as a c-type cytochrome (Lavergne 1983), an iron-sulfur protein (Bouges-Bocquet 1980), or an NADH dehydrogenase type protein cannot be ruled out (Meng et al 1986).…”

Section: Mechanism Of Cyclic Electron Transfermentioning

confidence: 99%

Structure and function of the chloroplast cytochrome bf complex

O’Keefe

1988

Photosynth Res

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The chloroplast cytochrome bf complex is an intrinsic multisubunit protein from the thylakoid membrane consisting of four polypeptides: cytochrome f, a two heme containing cytochrome b 6, the Rieske iron-sulfur protein, and a 17 kD polypeptide of undefined function. The complex functions in electron transfer between PSII and PSI, where most mechanisms suggest that the transfer of a single reducing equivalent from plastoquinol to plastocyanin results in the translocation of two protons across the membrane. Primary sequence analyses, dichroism studies, and functional considerations allow the construction of an approximate structural model of a monomeric complex, although some evidence exists for a dimeric structure. Resolution of the properties of the two cytochrome b 6 hemes has relied upon the availability of purified solubilized complex, while evidence in the thylakoid suggests the difference between the two hemes are not as great in situ. Such variability in the spectroscopic and electrochemical properties of the cytochrome b 6 is a major concern during the experimental use of the purified complex. There is a general consensus that the complex contains a plastoquinol oxidizing (Qz) site, although the evidence for a plastoquinone reduction (Qc) site, called for in most mechanistic hypotheses, is less substantive. Probably the most severe challenge to the so called Q-cycle mechanism comes from experimental observations made with cytochrome b 6 initially reduced, where proposed interpretations more closely resemble a b-cycle than a Q-cycle. Although functional during cyclic electron transfer, the role of the complex and its possible interaction with other proteins, has not been completely resolved.

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Evidence for a reluctant‐dependent oxidation of chloroplast cytochrome b‐563

Cited by 21 publications

References 20 publications

Evidence for two cyclic photophosphorylation reactions concurrent with ferredoxin-catalyzed non-cyclic electron transport

Evidence for two cyclic photophosphorylation reactions concurrent with ferredoxin-catalyzed non-cyclic electron transport

Sites of cytochromeb‐563 reduction, and the mode of action of DNP‐INT and DBMIB in the chloroplast cytochromeb‐563/fcomplex

Structure and function of the chloroplast cytochrome bf complex

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