Diazonium modification of Photosystem I. A specific effect on iron-sulfur Center B

Malkin, Richard

doi:10.1016/0005-2728(84)90141-5

Cited by 33 publications

(13 citation statements)

References 24 publications

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“…2B) and the D1 polypeptide of spinach PSII (Fig. 2C) (1,23). Under identical conditions, none of these four signals was observed in membranes from T398-1 (Fig.…”

Section: Resultsmentioning

confidence: 87%

Directed mutagenesis of an iron-sulfur protein of the photosystem I complex in the filamentous cyanobacterium Anabaena variabilis ATCC 29413.

Mannan

Whitmarsh

Nyman

et al. 1991

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

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In oxygenic photosynthetic organisms the PSI-C polypeptide, encoded by the psaC gene, provides the ligands for two centers, FA and FB, the terminal electron acceptors in the photosystem I (PSI) complex. An insertion mutation introduced in the psaC locus of the filamentous cyanobacteriumAnabaena variabils ATCC 29413 resulted in the creation of a mutant strain, T398-1, that lacks the PSI-C polypeptide. In medium supplemented with 5 mM fructose, the mutant cells grew well in the dark. However, when grown in the same medium under light, the doubling rate of T398-1 cells was significantly decreased. In intact cells of T398-1, bicarbonatedependent whole-chain electron transport (PSII and PSI) could not be detected, although partial electron transport reactions involving either one of the two photosystems could be measured at significant rates. The low-temperature EPR signals attributed to the [4Fe-4S] centers FA and FB were absent in the mutant cells. Chemical titration measurements indicated that the ratios of chlorophyll to the primary donor P700 were virtually identical in membranes from the wild-type and mutant cells. Moreover, room-temperature optical spectroscopic analysis of the thylakoid membranes isolated from T398-1 showed flash-induced P700 oxidation followed by dark rereduction, indicating primary photochemistry in PSI. Thus stable assembly of the reaction center of PSI can occur in the absence of the Fe-S cluster cofactors FA and FB. These studies demonstrate thatAnabaena 29413 offers a useful genetic system for targeted mutagenesis of the PSI complex.Photosystem I (PSI) is a membrane-bound pigment-protein complex that mediates electron transfer from reduced plastocyanin and cytochrome c553 to ferredoxin. Biochemical and biophysical analyses of thylakoid membranes and isolated PSI particles from cyanobacteria and higher plants have helped in formulating the functional organization of redox intermediates involved in the transfer of electrons from P700, the reaction-center chlorophyll(s) (Chl) of PSI, to ferredoxin.Five different electron-transfer intermediates-namely, A0, Al, Fx, FA, and FE-Nare known to be involved in electron transfer from P700 to ferredoxin (reviewed in ref.

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“…2B) and the D1 polypeptide of spinach PSII (Fig. 2C) (1,23). Under identical conditions, none of these four signals was observed in membranes from T398-1 (Fig.…”

Section: Resultsmentioning

confidence: 87%

Directed mutagenesis of an iron-sulfur protein of the photosystem I complex in the filamentous cyanobacterium Anabaena variabilis ATCC 29413.

Mannan

Whitmarsh

Nyman

et al. 1991

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

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“…Later, however, Golbeck and Warden [41] in a more detailed study showed that F a was lost at an earlier stage than was F A photoreduction and it was concluded that this was evidence against a linear sequence, Fa ~ F A . However, Malkin [71] showed that the presence of diazonium benzene sulphonate (DABS) preferentially inhibited Fa, and although still present and photoreducible at room temperature, F A photoreduction at cryogenic temperatures was lost. This was interpreted as evidence for a linear sequence.…”

Section: O4 Do Centers F a And F B Function In Forward Electron Tranmentioning

confidence: 99%

Primary photochemistry in photosystem-I

1985

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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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“…Their proposal cannot be considered to be supported by unambiguous evidence now, because Itoh et al (1987) later found that ethertreated vitamin K-l-free particles which cannot efficiently photoreduce iron-sulfur centers by the flash excitation at room temperature, can photoreduce F A by continuous illumination at cryogenic temperatures. Malkin (1984) found that diazonium benzene sulfonate selectively destroyed F B in chloroplasts and that the above treatment lead to a loss of PS I-dependent ferredoxin reduction. Although he found a marked inhibition of photoreduction of F g by continuous illumination at cryogenic temperatures, no flash experiments at room temperature were reported.…”

Section: Introductionmentioning

confidence: 99%

Effects of selective destruction of iron-sulfur center B on electron transfer and charge recombination in Photosystem I

1991

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Incubation of spinach thylakoids with HgCl2 selectively destroys Fe-S center B (FB). The function of electron acceptors in FB-less PS I particles was studied by following the decay kinetics of P700(+) at room temperature after multiple flash excitation in the absence of a terminal electron acceptor. In untreated particles, the decay kinetics of the signal after the first and the second flashes were very similar (t 1/2∼2.5 ms), and were principally determined by the concentration of the artificial electron donor added. The decay after the third flash was fast (t 1/2∼0.25 ms). In FB-less particles, although the decay after the first flash was slow, fast decay was observed already after the second flash. We conclude that in FB-less particles, electron transfer can proceed normally at room temperature from FX to FA and that the charge recombination between P700(+) and FX (-)/A1 (-) predominated after the second excitation. The rate of this recombination process is not significantly affected by the destruction of FB. Even in the presence of 60% glycerol, FB-less particles can transfer electrons to FA at room temperature as efficiently as untreated particles.

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Diazonium modification of Photosystem I. A specific effect on iron-sulfur Center B

Cited by 33 publications

References 24 publications

Directed mutagenesis of an iron-sulfur protein of the photosystem I complex in the filamentous cyanobacterium Anabaena variabilis ATCC 29413.

Directed mutagenesis of an iron-sulfur protein of the photosystem I complex in the filamentous cyanobacterium Anabaena variabilis ATCC 29413.

Primary photochemistry in photosystem-I

Effects of selective destruction of iron-sulfur center B on electron transfer and charge recombination in Photosystem I

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