The absence of a spectroscopically resolved intermediate state P<sup>+</sup>B<sup>−</sup>in bacterial photosynthesis

Breton, Jacques; Martin, Jean−Louis; Petrich, Jacob W.; Migus, A.; Antonetti, A.

doi:10.1016/0014-5793(86)81080-8

Cited by 65 publications

(48 citation statements)

References 24 publications

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“…The picture of spectral evolution that emerges from this study is clearly more complicated than that which could be extracted from early studies of our (10,13,19) and other (11,26) groups. The spectral evolution of the stimulated emission (Fig.…”

Section: Discussionmentioning

confidence: 60%

“…50 mM dithiothreitol to ensure complete back reaction between the flashes (17). At room temperature, this treatment has a similar effect (slower overall kinetics) as reduction with sodium dithionite (19), but reduction with dithiothreitol was found to be much more stable. The samples were diluted in 60o (vol/vol) glycerol to an OD of 0.5 at 870 nm in a cuvette with an optical path of 1 mm and were cooled in the darkj to 10 K in a convection cryostat.…”

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confidence: 95%

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Femtosecond spectral evolution of the excited state of bacterial reaction centers at 10 K.

Vos

Lambry

Robles

et al. 1992

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

110

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The femtosecond spectral evolution of reaction centers of Rhodobacter sphaeroides R-26 was studied at 10 K. Transient spectra in the near infrared region, obtained with 45-fs pulses (pump pulses centered at 870 um and continuum probe pulses), were analyzed with associated kinetics at specific wavelengths. The reaction center of photosynthetic purple bacteria contains an ensemble of six chromophores, which are bound to two protein subunits L and M (1, 2). Two of the chromophores are bacteriopheophytins (HL and HM); the other four are the bacteriochlorophylls PL, PM, BL, and BM. It is generally accepted that the former two are strongly coupled; they are referred to as the special pair P. Furthermore, not only PL and PM, but all chromophores display at least some degree of interaction. The ground state absorption spectrum in principle may consist of bands that each contain contributions of all six chromophores. The individual Qy bands are usually named after the chromophores that are thought to provide the major contribution-i.e., B (BL and BM), for Rhodobacter sphaeroides around 800 nm, and H (HL and HM) around 750 nm, and the exciton bands of P (P-around 890 nm at cryogenic temperatures; P+ around 810 nm). In addition to interchromophore interactions, the spectrum presumably is influenced by charge transfer transitions (3, 4) and by electrostatic interactions with the protein solvent (5-7). Various calculations of exciton interactions have been published, but the degree of excitonic coupling, the environmental influences, and the possible contribution of charge transfer transitions to the spectrum are still subject to debate (5-7). An alteration of the electronic state is bound to perturb any interaction and, viewing the reaction center as an interacting hexamer, modify all bands. For example, compared to that of the singlet ground state, the triplet spectrum displays considerable changes in the B bands and also minor perturbations of the H bands, apart from the very strong changes in the P bands (8). These features have been explained in terms of excitonic coupling (9). The assessment of interpigment and pigment-protein interactions may prove essential to understand the nature ofthe extremely fast electron transport in the reaction center. Therefore, of high functional interest is the spectrum of the lowest singlet excited state of the reaction center pigment system P*, which is the precursor of electron transport. The kinetics of this state are most easily probed by its stimulated emission. In active R. sphaeroides reaction centers, it decays initially with a time constant of -3 ps at room temperature (10-12) and 1.2 ps at 10 K (13, 14). The charge pair P+HjL emerges with about the same time constant, as probed by the appearance of an electrochromic shift of the B band and the bleaching of the HL band (10,11,13).Recent data indicate that the spectrum of the reaction center also evolves on a time scale faster than the electron transfer from P to HL. At room temperature, a kinetic component with a time co...

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Section: Discussionmentioning

confidence: 60%

mentioning

confidence: 95%

Femtosecond spectral evolution of the excited state of bacterial reaction centers at 10 K.

Vos

Lambry

Robles

et al. 1992

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

110

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“…sphaeroides and Rps. viridis RCs have been based largely on the finding of identical kinetics for the decay of P* and the formation of P+BPhF~ [4][5][6][7][8]. Our spectral data provide a new measure of the extent to which the conversion of P* to P+BPhF~ may involve an intermediate state.…”

Section: Mechanism Of the Initial Electron Transfer Reactionmentioning

confidence: 94%

Subpicosecond characterization of the optical properties of the primary electron donor and the mechanism of the initial electron transfer in Rhodobacter capsulatus reaction centers

Kirmaier

Holten

1988

FEBS Letters

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The optical difference spectrum of the excited primary electron donor, P*, in Rb. capsulatus reaction centers has been measured 600 fs after a 350‐fs flash at 870 nm. The spectrum is characterized by bleaching in the ground state absorption bands at 855 and 600 nm, and a weak featureless transient absorption in between. The lack of significant (if any) bleaching at 800 nm indicates that P does not contribute appreciable oscillator strength to the 800‐nm ground state absorption band. The conversion of P* to P+BPH− L is accompanied by isosbestic points in the transient difference spectra at 765 and 798 nm. The existence of the longer‐wavelength isosbestic point, occurring essentially at the near‐infrared absorbance maximum of the accessory BChls, provides compelling evidence that if state P*BChl− L forms, its transient concentration is exceedingly small. At certain wavelengths in the near‐infrared the absorption changes develop somewhat more slowly than the rate at which P* decays, a finding that may reflect a contribution from readjustments in the pigment‐protein complex in response to electron transfer.

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“…sphaeroMes [24]. (3) Electron transport is unimpaired in borohydride-treated RC [35][36][37][38][39]. (4) Borohydride modification is inhibited in wild-type RC, which contain one carotenoid per RC, bound in close proximity to and apparently protecting the BChl in B M [2,4].…”

Section: Discussionmentioning

confidence: 99%

Modified bacterial reaction centers. 4. The borohydride treatment reinvestigated: comparison with selective exchange experiments at binding sites BA,B and HA,B

Struck¹,

Müller²,

Scheer³

1991

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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Pigments of borohydride-treated reaction centers of Rhodobacter sphaeroides R 26 and Rhodopseudomonas viridiswere analyzed by HPLC with polychromatie detection. In both species, pigment composition and contents were unchanged. Reaction centers from Rhodobacter sphaeroides R26 were prepared in which bacteriochlorophylls (B A B) and bacteriopheophytins (HA, n) were exchanged with their potential borohydride products reduced at C-3 t.[3-Hydroxyethyl]-BChl a exchanges selectively into the BA, B pockets, and 31-OH-BPh a to the HA, B pockets. Stable reaction centers are obtained in both cases. A comparison of the absorption and circular dichroism spectra of reaction centers after exchange with 31-OH pigments, and of borohydride-modified reaction centers, reveal distinct differences. It is concluded that during borohydride reduction none of the pigments is chemically modified or extracted from the reaction centers.

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The absence of a spectroscopically resolved intermediate state P⁺B⁻in bacterial photosynthesis

Cited by 65 publications

References 24 publications

Femtosecond spectral evolution of the excited state of bacterial reaction centers at 10 K.

Femtosecond spectral evolution of the excited state of bacterial reaction centers at 10 K.

Subpicosecond characterization of the optical properties of the primary electron donor and the mechanism of the initial electron transfer in Rhodobacter capsulatus reaction centers

Modified bacterial reaction centers. 4. The borohydride treatment reinvestigated: comparison with selective exchange experiments at binding sites BA,B and HA,B

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The absence of a spectroscopically resolved intermediate state P+B−in bacterial photosynthesis

Cited by 65 publications

References 24 publications

Femtosecond spectral evolution of the excited state of bacterial reaction centers at 10 K.

Femtosecond spectral evolution of the excited state of bacterial reaction centers at 10 K.

Subpicosecond characterization of the optical properties of the primary electron donor and the mechanism of the initial electron transfer in Rhodobacter capsulatus reaction centers

Modified bacterial reaction centers. 4. The borohydride treatment reinvestigated: comparison with selective exchange experiments at binding sites BA,B and HA,B

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The absence of a spectroscopically resolved intermediate state P⁺B⁻in bacterial photosynthesis