Very fast electron transfer from cytochrome to the bacterial photosynthetic reaction center at low temperature

Ortega, José M.; Dohse, Barbara; Oesterhelt, Dieter; Mathis, Paul

doi:10.1016/s0014-5793(96)01440-8

Cited by 14 publications

(12 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…ϳ20% at ϳ200 K). Below this temperature, the amplitude of this phase abruptly decreases with decreasing temperature, reaching 0% below 150 K. Data of cytochrome oxidation below 150 K in WT strain are very similar, and have been reported previouly (Ortega and Mathis, 1993;Ortega et al, 1997). The weight of the VS component attributed to the P ϩ Q A Ϫ back-reaction increases with decreasing temperature in L162Y, L162F, and L162W strains from a value of 2% at 294 K to a maximum value of nearly 90 -97% of the total amplitude of P ϩ rereduction below 150 K (85% for L162W at 150 K).…”

Section: Effect Of Temperature On the Extent Of Phases Of P ؉ Reductionsupporting

confidence: 79%

“…3 shows the temperature dependence of the amplitudes of the VF, F, and VS components of P ϩ rereduction after a single laser flash. Data for the L162T strain have recently been published in a separate paper (Ortega et al, 1997). Table 2 summarizes the amplitude values of the sum of both fast components (VF and F) at seven different temperatures in the seven strains of Rps.…”

Section: Effect Of Temperature On the Extent Of Phases Of P ؉ Reductionmentioning

confidence: 99%

See 1 more Smart Citation

Low-Temperature Electron Transfer from Cytochrome to the Special Pair in Rhodopseudomonas viridis: Role of the L162 Residue

Ortega

Dohse

Oesterhelt

et al. 1998

Biophysical Journal

Self Cite

View full text Add to dashboard Cite

Electron transfer from the tetraheme cytochrome c to the special pair of bacteriochlorophylls (P) has been studied by flash absorption spectroscopy in reaction centers isolated from seven strains of the photosynthetic purple bacterium Rhodopseudomonas viridis, where the residue L162, located between the proximal heme c-559 and P, is Y (wild type), F, W, G, M, T, or L. Measurements were performed between 294 K and 8 K, under redox conditions in which the two high-potential hemes of the cytochrome were chemically reduced. At room temperature, the kinetics of P+ reduction include two phases in all of the strains: a dominant very fast phase (VF), and a minor fast phase (F). The VF phase has the following t(1/2): 90 ns (M), 130 ns (W), 135 ns (F), 189 ns (Y; wild type), 200 ns (G), 390 ns (L), and 430 ns (T). These data show that electron transfer is fast whatever the nature of the amino acid at position L162. The amplitudes of both phases decrease suddenly around 200 K in Y, F, and W. The effect of temperature on the extent of fast phases is different in mutants G, M, L, and T, in which electron transfer from c-559 to P+ takes place at cryogenic temperatures in a substantial fraction of the reaction centers (T, 48%; G, 38%; L, 23%, at 40 K; and M, 28%, at 60 K), producing a stable charge separated state. In these nonaromatic mutants the rate of VF electron transfer from cytochrome to P+ is nearly temperature-independent between 294 K and 8 K, remaining very fast at very low temperatures (123 ns at 60 K for M; 251 ns at 40 K for L; 190 ns at 8 K for G, and 458 ns at 8 K for T). In all cases, a decrease in amplitudes of the fast phases is paralleled by an increase in very slow reduction of P+, presumably by back-reaction with Q(A)-. The significance of these results is discussed in relation to electron transfer theories and to freezing at low temperatures of cytochrome structural reorganization.

show abstract

Section: Effect Of Temperature On the Extent Of Phases Of P ؉ Reductionsupporting

confidence: 79%

Section: Effect Of Temperature On the Extent Of Phases Of P ؉ Reductionmentioning

confidence: 99%

Low-Temperature Electron Transfer from Cytochrome to the Special Pair in Rhodopseudomonas viridis: Role of the L162 Residue

Ortega

Dohse

Oesterhelt

et al. 1998

Biophysical Journal

Self Cite

View full text Add to dashboard Cite

show abstract

“…sphaeroides and in the Rps. viridis reaction centers has been discussed extensively (see Mathis et al, 1994;Ortega et al, 1997), placing a special emphasis on the role of structured water molecules.…”

Section: Behavior At Low Temperaturementioning

confidence: 99%

Effects of Temperature and ΔG° on Electron Transfer from Cytochrome c2 to the Photosynthetic Reaction Center of the Purple Bacterium Rhodobacter sphaeroides

Venturoli

Drepper

Williams

et al. 1998

Biophysical Journal

View full text Add to dashboard Cite

The kinetics of electron transfer from cytochrome c2 to the primary donor (P) of the reaction center from the photosynthetic purple bacterium Rhodobacter sphaeroides have been investigated by time-resolved absorption spectroscopy. Rereduction of P+ induced by a laser pulse has been measured at temperatures from 300 K to 220 K in a series of specifically mutated reaction centers characterized by altered midpoint redox potentials of P+/P varying from 410 mV to 765 mV (as compared to 505 mV for wild type). Rate constants for first-order electron donation within preformed reaction center-cytochrome c2 complexes and for the bimolecular oxidation of free cytochrome c2 have been obtained by multiexponential deconvolution of the kinetics. At all temperatures the rate of the fastest intracomplex electron transfer increases by more than two orders of magnitude as the driving force -deltaGo is varied over a range of 350 meV. The temperature and deltaGo dependences of the rate constant fit the Marcus equation well. Global analysis yields a reorganization energy lambda = 0.96 +/- 0.07 eV and a set of electronic matrix elements, specific for each mutant, ranging from 1.2 10(-4) eV to 2.5 10(-4) eV. Analysis in terms of the Jortner equation indicates that the best fit is obtained in the classical limit and restricts the range of coupled vibrational modes to frequencies lower than approximately 200 cm(-1). An additional slower kinetic component of P+ reduction, attributed to electron transfer from cyt c2 docked in a nonoptimal configuration of the complex, displays a Marcus type dependence of the rate constant upon deltaGo, characterized by a similar value of lambda (0.8 +/- 0.1 eV) and by an average electronic matrix element smaller by more than one order of magnitude. In all of the mutants, as the temperature is decreased below 260 K, both intracomplex reactions are abruptly inhibited, their rate being negligible at 220 K. The free energy dependence of the second-order rate constant for oxidation of cyt c2 in solution suggests that the collisional reaction is partially diffusion controlled, reaching the diffusion limit at exothermicities between 150 and 250 meV over the temperature range investigated.

show abstract

“…This attribute led to the assumption that this tyrosine residue plays a critical role in the cytochrome-mediated reduction of the photo-oxidized BChl dimer [83,84]. In attempts to understand its function, this tyrosine has been replaced by other amino acids through site-directed mutagenesis in B. viridis [45,73,85] and in R. sphaeroides [32,86,87]. These analyses established the role of this residue as mainly structural.…”

Section: Discussionmentioning

confidence: 99%

“…Analyses of the redox properties of the individual hemes have shown an alternation of low—high—low—high midpoint potentials in the spatial arrangement of the four hemes in the cytochrome subunit, with the highest potential heme C 380 (heme 1) located proximally to P [40,41]. The different ET steps from cytochrome have been characterized [42], including restrictions that occur at cryogenic temperatures [43-45]. In addition, the presence of cytochrome, which served as an internal electron donor, was a crucial factor for the determination of the primary acceptor and the intermediate ET carriers at very early stages in the investigation of photosynthesis [46,47].…”

Section: Introductionmentioning

confidence: 99%

Structural and spectropotentiometric analysis of Blastochloris viridis heterodimer mutant reaction center

Ponomarenko¹,

Li²,

Marino³

et al. 2009

Biochimica et Biophysica Acta (BBA) - Biomembranes

View full text Add to dashboard Cite

Heterodimer mutant reaction centers (RCs) of Blastochloris viridis were crystallized using microfluidic technology. In this mutant, a leucine residue replaced the histidine residue which had acted as a fifth ligand to the bacteriochlorophyll (BChl) of the primary electron donor dimer M site (HisM200). With the loss of the histidine-coordinated Mg, one bacteriochlorophyll of the special pair was converted into a bacteriopheophytin (BPhe), and the primary donor became a heterodimer supermolecule. The crystals had dimensions 400×100×100 μm, belonged to space group P43212, and were isomorphous to the ones reported earlier for the wild type (WT) strain. The structure was solved to a 2.5 Å resolution limit. Electron-density maps confirmed the replacement of the histidine residue and the absence of Mg. Structural changes in the heterodimer mutant RC relative to the WT included the absence of the water molecule that is typically positioned between the M side of the primary donor and the accessory BChl, a slight shift in the position of amino acids surrounding the site of the mutation, and the rotation of the M194 phenylalanine. The cytochrome subunit was anchored similarly as in the WT and had no detectable changes in its overall position. The highly conserved tyrosine L162, located between the primary donor and the highest potential heme C380, revealed only a minor deviation of its hydroxyl group. Concomitantly to modification of the BChl molecule, the redox potential of the heterodimer primary donor increased relative to that of the WT organism (772 mV vs. 517 mV). The availability of this heterodimer mutant and its crystal structure provides opportunities for investigating changes in light-induced electron transfer that reflect differences in redox cascades.

show abstract

Very fast electron transfer from cytochrome to the bacterial photosynthetic reaction center at low temperature

Cited by 14 publications

References 29 publications

Low-Temperature Electron Transfer from Cytochrome to the Special Pair in Rhodopseudomonas viridis: Role of the L162 Residue

Low-Temperature Electron Transfer from Cytochrome to the Special Pair in Rhodopseudomonas viridis: Role of the L162 Residue

Effects of Temperature and ΔG° on Electron Transfer from Cytochrome c2 to the Photosynthetic Reaction Center of the Purple Bacterium Rhodobacter sphaeroides

Structural and spectropotentiometric analysis of Blastochloris viridis heterodimer mutant reaction center

Contact Info

Product

Resources

About