The thermodynamic characteristic of four‐heme cytochrome <i>c</i> in <i>Rhodopseudomonas viridis</i> reaction centers, as derived from a quantitative analysis of the differential absorption spectra in α‐domain

Shinkarev, Vladimir P.; Drachev, Alexander L.; Dracheva, Stella

doi:10.1016/0014-5793(90)80624-r

Cited by 24 publications

(8 citation statements)

References 11 publications

(1 reference statement)

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“…The extent of the reaction between reduced cytochrome c2 and photooxidized cytochrome c-556 was consistent with a redox potential difference of 0.03 ±0.01 V between the two cytochromes. This is in good agreement with the previously measured redox potentials, which are 285 mV for cytochrome c2 (Pettigrew et al, 1978) and 312 mV for cytochrome c-556 (Shinkarev et al, 1990). Oxidized cytochrome c2 did not inhibit the reaction of reduced cytochrome c2 with cytochrome c-556, indicating that the dissociation constant of oxidized cytochrome c2 was greater than 50 mM.…”

Section: Discussionsupporting

confidence: 92%

“…Recent EPR and kinetic studies have indicated that the hemes are arranged in the order BChl dimer, (Nitschke & Rutherford, 1989;Dracheva et al, 1988;Vermeglio et al, 1989). Redox titration studies have shown that the room temperature midpoint potentials of the four hemes are the following: c-559, +360 mV; c-552, +20 mV; c-556, +312 mV; c-554, <-50 mV (Shinkarev et al, 1990;Dracheva et al, 1986; Alegria & Dutton, 1987). It is interesting that the low-potential heme c-552 is positioned between the two high-potential hemes, since only the latter are reduced under physiological conditions.…”

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confidence: 99%

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Reaction of cytochrome c2 with photosynthetic reaction centers from Rhodopseudomonas viridis

Knaff

Willie²,

Long³

et al. 1991

Biochemistry

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The reactions of Rhodopseudomonas viridis cytochrome c2 and horse cytochrome c with Rps. viridis photosynthetic reaction centers were studied by using both single- and double-flash excitation. Single-flash excitation of the reaction centers resulted in rapid photooxidation of cytochrome c-556 in the cytochrome subunit of the reaction center. The photooxidized cytochrome c-556 was subsequently reduced by electron transfer from ferrocytochrome c2 present in the solution. The rate constant for this reaction had a hyperbolic dependence on the concentration of cytochrome c2, consistent with the formation of a complex between cytochrome c2 and the reaction center. The dissociation constant of the complex was estimated to be 30 microM, and the rate of electron transfer within the 1:1 complex was 270 s-1. Double-flash experiments revealed that ferricytochrome c2 dissociated from the reaction center with a rate constant of greater than 100 s-1 and allowed another molecule of ferrocytochrome c2 to react. When both cytochrome c-556 and cytochrome c-559 were photooxidized with a double flash, the rate constant for reduction of both components was the same as that observed for cytochrome c-556 alone. The observed rate constant decreased by a factor of 14 as the ionic strength was increased from 5 mM to 1 M, indicating that electrostatic interactions contributed to binding. Molecular modeling studies revealed a possible cytochrome c2 binding site on the cytochrome subunit of the reaction center involving the negatively charged residues Glu-93, Glu-85, Glu-79, and Glu-67 which surround the heme crevice of cytochrome c-554.(ABSTRACT TRUNCATED AT 250 WORDS)

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Section: Discussionsupporting

confidence: 92%

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confidence: 99%

Reaction of cytochrome c2 with photosynthetic reaction centers from Rhodopseudomonas viridis

Knaff

Willie²,

Long³

et al. 1991

Biochemistry

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“…The purpose of this subunit and how it might alter the specificity of the reaction center toward soluble electron donors are unknown. It has been shown that each of the four hemes of the bound cytochrome has a distinctive redox potential, absorption spectrum, and orientation relative to the bacteriochlorophyll-containing subunits (Dracheva et al, 1986(Dracheva et al, ,1988Vermeglio et al, 1989;Fritzsch et al, 1989; Nitschke & Rutherford, 1989;Shinkarev et al, 1990;Nitschke et al, 1992;Fritz et al, 1992). The redox potentials of the four hemes also have been rationalized on the basis of the three-dimensional structure (Gunner & Honig, 1991).…”

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confidence: 99%

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

Meyer¹,

Bartsch²,

Cusanovich³

et al. 1993

Biochemistry

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The photosynthetic reaction center of Rhodopseudomonas viridis contains a bound tetraheme cytochrome c subunit which is the primary electron donor to the photooxidized special pair bacteriochlorophyll. We have tested a variety of soluble electron-transfer proteins for their ability to serve as secondary electron donors to the bacteriochlorophyll via the bound cytochrome by measuring the kinetics of reaction center heme reduction following photooxidation by a laser flash, as a function of soluble protein concentration and ionic strength. All of the soluble redox proteins utilized appear to interact with a negatively charged region on the reaction center and to transfer electrons to the 300-mV heme c-556 of the bound cytochrome. Rps. viridis cytochrome c2 was the best electron donor among those proteins tested, with a second-order rate constant extrapolated to infinite ionic strength of 1.2 x 10(6) M-1 s-1, which is two orders of magnitude larger than that of horse cytochrome c. Rps. viridis cytochrome c2 apparently binds to the reaction center at low ionic strength, as evidenced by a nonlinear dependence of kobs on protein concentration. The limiting first-order electron-transfer rate constant at 6 mM ionic strength is approximately 1300 s-1. Horse cytochrome c and the reaction center also form a complex, with a limiting first-order rate constant for electron transfer which is 5 times smaller than for cytochrome c2. Other cytochromes c2 are intermediate in reactivity. More distantly related cytochromes, HiPIP, and azurin are relatively poor electron donors under the conditions of assay.(ABSTRACT TRUNCATED AT 250 WORDS)

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“…This subunit consist of the four c‐type cytochromes, which are labeled as c554, c556, c552, and c559, the number being the wave number of the α‐peak in the absorption spectra. The roles of these four hemes have been studied by various methods,3–7 since the structure of the reaction center was determined by X‐ray chrystallography 2. Despite the large distance (8.7 Å) between P and c559, which is the proximate chromophore to P in the cytochrome subunit, rather fast electron transfer (120–220 ns) has been observed 8–11.…”

Section: Introductionmentioning

confidence: 99%

Electron transfer in the c-type cytochrome subunit of the photosynthetic reaction center ofRhodopseudomonas viridis:ab initio theoretical study

2001

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ABSTRACT:The pathways of the electron transfers (ETs) within the c-type cytochrome subunit and from the cytochrome subunit to the oxidized special pair (P + ) in the reaction center of Rhodopseudomonas viridis were studied by calculating the transfer integrals among the chromophores and the bridging amino acid residues by ab initio molecular orbital method. In the cytochrome subunit, the candidate of the bridge molecules was selected by the criterion of the distance from the two neighboring hemes, and the calculated results indicate that the ET occurs directly from a heme to the next heme. From c559, the proximate heme to the special pair, to P + , the ET occurs mainly through TYR L162, which lies halfway between c559 and P + , because of its proper location. Furthermore, the mutation experiments in which TYR L162 was replaced by phenylalanine and threonine were examined by the same theoretical method, and it was shown that the result of the mutation experiment was understood by the difference in the spatial distribution of the MOs between the wild type and mutants, and not by the energy difference of the MOs between donor (or acceptor) and bridge, though the latter factor had often been considered as the main factor controlling the rate of the ET.

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The thermodynamic characteristic of four‐heme cytochrome c in Rhodopseudomonas viridis reaction centers, as derived from a quantitative analysis of the differential absorption spectra in α‐domain

Cited by 24 publications

References 11 publications

Reaction of cytochrome c2 with photosynthetic reaction centers from Rhodopseudomonas viridis

Reaction of cytochrome c2 with photosynthetic reaction centers from Rhodopseudomonas viridis

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

Electron transfer in the c-type cytochrome subunit of the photosynthetic reaction center ofRhodopseudomonas viridis:ab initio theoretical study

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