Kinetics of photooxidation of soluble cytochromes, HiPIP, and azurin by the photosynthetic reaction center of the purple phototrophic bacterium Rhodopseudomonas viridis

Meyer, Terry E.; Bartsch, Robert G.; Cusanovich, M.A.; Tollin, Gordon

doi:10.1021/bi00069a005

Cited by 39 publications

(42 citation statements)

References 41 publications

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“…protein-protein electron transfer rate constants (Meyer et al, , 1987(Meyer et al, , 1993a(Meyer et al, , 1993b(Meyer et al, , 1993cTollin et al, 1984Tollin et al, , 1986Tollin et al, , 1993Przysiecki et al, 1985;Cheddar et al, 1986Cheddar et al, , 1989. In all cases where the experimental data show a monotonic increase or decrease in rate constant with ionic strength, the rate constant versus square root of ionic strength curves can be fit using the parallel plate model monopole term (K;) only.…”

Section: Ja Watkins Et Almentioning

confidence: 99%

A “parallel plate” electrostatic model for bimolecular rate constants applied to electron transfer proteins

et al. 1994

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A "parallel plate" model describing the electrostatic potential energy of protein-protein interactions is presented that provides an analytical representation of the effect of ionic strength on a bimolecular rate constant. The model takes into account the asymmetric distribution of charge on the surface of the protein and localized charges at the site of electron transfer that are modeled as elements of a parallel plate condenser. Both monopolar and dipolar interactions are included. Examples of simple (monophasic) and complex (biphasic) ionic strength dependencies obtained from experiments with several electron transfer protein systems are presented, all of which can be accommodated by the model. The simple cases do not require the use of both monopolar and dipolar terms (i.e., they can be fit well by either alone). The biphasic dependencies can be fit only by using dipolar and monopolar terms of opposite sign, which is physically unreasonable for the molecules considered. Alternatively, the high ionic strength portion of the complex dependencies can be fit using either the monopolar term alone or the complete equation; this assumes a model in which such behavior is a consequence of electron transfer mechanisms involving changes in orientation or site of reaction as the ionic strength is varied. Based on these analyses, we conclude that the principal applications of the model presented here are to provide information about the structural properties of intermediate electron transfer complexes and to quantify comparisons between related proteins or site-specific mutants. We also conclude that the relative contributions of monopolar and dipolar effects to protein electron transfer kinetics cannot be evaluated from experimental data by present approximations.

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Section: Ja Watkins Et Almentioning

confidence: 99%

A “parallel plate” electrostatic model for bimolecular rate constants applied to electron transfer proteins

et al. 1994

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“…HiPIPs are abundant in most species of purple phototrophic bacteria that lack cytochrome c2 (25). They have been extensively investigated as electron-transfer models (24,(30)(31)(32)(33), and their structural and spectroscopic properties are well characterized (34). Although they have the right reduction potential (+90 to +450 mV) to couple bc1 and RC complexes (32), suggesting a role in cyclic photosynthetic electron transfer, their physiological function is still a matter for discussion.…”

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confidence: 99%

“…sphaeroides (13)(14)(15)(16)(17)(18)(19)(20)(21), in Rps. viridis, it reacts with the tetraheme subunit (22)(23)(24). Only about half of the purple bacterial species described so far contain cytochrome c2 (25), and it is not known how the remaining species carry out electron transfer between the bc1 and RC complexes.…”

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confidence: 99%

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Kinetics of photo-induced electron transfer from high-potential iron-sulfur protein to the photosynthetic reaction center of the purple phototroph Rhodoferax fermentans.

Hochkoeppler

Zannoni

Ciurli

et al. 1996

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

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The kinetics of photo-induced electron transfer from high-potential iron-sulfur protein (HiPIP) to the photosynthetic reaction center (RC) of the purple phototroph Rhodoferaxfermentans were studied. The rapid photooxidation of heme c-556 belonging to RC is followed, in the presence of HiPIP, by a slower reduction having a second-order rate constant of4.8 x 107 M -l s -1. The limiting value of k.bs at high HiPIP concentration is 95 s-1. The amplitude of this slow process decreases with increasing HiPIP concentration. The amplitude of a faster phase, observed at 556 and 425 nm and involving heme c-556 reduction, increases proportionately. The rate constant of this fast phase, determined at 425 and 556 nm, is -3 x 105 s-1. This value is not dependent on HiPIP concentration, indicating that it is related to a first-order process. These observations are interpreted as evidence for the formation of a HiPIP-RC complex prior to the excitation flash, having a dissociation constant of -2.5 ,uM. The fast phase is absent at high ionic strength, indicating that the complex involves mainly electrostatic interactions. The ionic strength dependence of kobs for the slow phase yields a second-order rate constant at infinite ionic strength of 5.4 x 106 M-t.s-I and an electrostatic interaction energy of -2.1 kcal/mol (1 cal = 4.184 J). We conclude that Rhodoferax fermentans HiPIP is a very effective electron donor to the photosynthetic RC.Anoxygenic phototrophic bacteria contain two membranebound components that are essential for energy production, the photosynthetic reaction center (RC) and the cytochrome bc1 complex. Two types of RC have been structurally characterized: the RC from Rhodobacter sphaeroides is made of three subunits (1, 2), while, in addition to these, RC from Rhodopseudomonas viridis contains a fourth tetraheme cytochrome c subunit (2, 3). InRps. viridis the four heme groups have a bands at 559, 552, 556, and 554 nm, and reduction potentials of +380 mV, +20 mV, +310 mV, and -60 mV, respectively (4). The four hemes are arranged in an almost linear fashion, (2,5,6) and are aligned in the sequence P/c-559/c-552/c-556/c-554, where P indicates the bacteriochlorophyll special pair (4, 7). The highest potential heme (c-559) is oxidized the most rapidly (t/2 -300 ns) by the photooxidized P (P+), followed by a slower oxidation of heme c-556 (ti/2 2 ,us) (4,8,9). The quinol generated by RC photooxidation is utilized by the bc1 complex to reduce cytochrome c2 (10), a soluble protein closely related to mitochondrial cytochrome c (11,12). Cytochrome c2 then reduces the photooxidized RC, closing the photocycle. However, although cytochrome c2 reacts directly with P+ in Rb. sphaeroides (13-21), in Rps. viridis, it reacts with the tetraheme subunit (22-24). Only about half of the purple bacterial species described so far contain cytochrome c2 (25), and it is not known how the remaining species carry out electron transfer between the bc1 and RC complexes.The RC from the purple nonsulfur bacterium Rhodoferax fermentans (26)...

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“…This indicates that the quinol oxidase, which accepts electrons from the RC-generated quinols, is not saturated under our experimental conditions. These findings suggest that electron transfer would occur between HiPIP and RC, possibly via the formation of a complex, as previously observed in analogous photosynthetic systems involving soluble c-type cytochromes and RCs [11,[20][21][22]. To test this hypothesis, we analyzed, using kinetic spectrophotometry, the absorbance changes related to RC-induced cytochrome oxidation.…”

Section: Resultsmentioning

confidence: 57%

The high potential iron‐sulfur protein (HiPIP) from Rhodoferax fermentans is competent in photosynthetic electron transfer

Hochkoeppler¹,

Ciurli²,

Venturoli³

et al. 1995

FEBS Letters

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Kinetics of photooxidation of soluble cytochromes, HiPIP, and azurin by the photosynthetic reaction center of the purple phototrophic bacterium Rhodopseudomonas viridis

Cited by 39 publications

References 41 publications

A “parallel plate” electrostatic model for bimolecular rate constants applied to electron transfer proteins

A “parallel plate” electrostatic model for bimolecular rate constants applied to electron transfer proteins

Kinetics of photo-induced electron transfer from high-potential iron-sulfur protein to the photosynthetic reaction center of the purple phototroph Rhodoferax fermentans.

The high potential iron‐sulfur protein (HiPIP) from Rhodoferax fermentans is competent in photosynthetic electron transfer

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