Simulation of optical spectra from the reaction center of Rhodopseudomonas viridis

Won, Youjip; Friesner, Richard A.

doi:10.1021/j100319a025

Cited by 61 publications

(57 citation statements)

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“…sphaeroides and Rps. viridis RCs has been deduced from recent measurements (20)(21)(22)(23) and calculations of the RC absorption spectrum (24,25 (12)(13)(14). Equally intriguing is the result that the inherent rate of decay of D* to the ground state (k1) appears to be -(30 ps)-1.…”

Section: Discussionmentioning

confidence: 99%

Electron transfer in a genetically modified bacterial reaction center containing a heterodimer.

Kirmaier

Holten

Bylina

et al. 1988

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

114

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Time-resolved optical measurements encompassing the femtoseconds to seconds time scales have been used to investigate Rhodobacter capsulatus reaction centers (RCs) in which the histidine residue at position 200 on the M polypeptide has been changed to a leucine by site-directed mutagenesis. TheHisM'' --) Leu RC, which has a heterodimer consisting of a bacteriochlorophyll and a bacteriopheophytin, is capable of the primary photochemistry observed in wild-type Rb. capsulatus RCs, but with an overall quantum yield reduced by about half. The lower yield resides in the initial electron transfer reaction and may be associated in part with substantial charge transfer character of the excited heterodimer. These and other comparisons between Rb. capsulatus wild-type and HisM2 -Leu RCs have important implications for our understanding of the mechanism of electron transfer in the RC and the efficiency of the charge separation process. MATERIALS AND METHODSIsolation of Rb. capsulatus wild-type and HiSM21 --Leu RCs followed described procedures (6, 7). The results of measurements performed on two different preparations of HiSM21 -+ Leu mutant RCs agreed within experimental error. The same is true of the measurements on wild-type Rb. capsulatus RCs. For both the mutant and wild-type RCs, a small portion of each preparation was extracted into acetone/methanol (7:2) and the pigment content was assayed via the Qy absorption bands of the extracted chromophores.The procedure closely followed that originally used for analysis ofRhodospirillum rubrum RCs (8). Determination of the total number of pigments per RC requires knowledge of the absolute extinction coefficient of some band in the RC spectrum. Since extinction coefficients have not been determined for Rb. capsulatus, we used the Rb. sphaeroides extinction coefficient at 802 nm of 288 mM -1 cm-l (9) for both wild-type and mutant RCs. The pigment ratio, on the other hand, is solely based on the near-infrared extinction coefficients of BChl and BPh in acetone/methanol (7:2), numbers that are given in ref. 8.Transient absorption spectra and kinetics were recorded on a spectrometer that utilizes 350-fs flashes. The optical pulses are generated with off-the-shelf laser equipment (Spectra Physics, Santa Clara, CA) and the vidicon-based detection system (PAR) is similar to that used on a picosecond spectrometer previously described (10). (Further details of the femtosecond apparatus will be given elsewhere.) The 350-fs 582-nm excitation flashes were attenuated so that 25-40% of the long-wavelength dimer band was bleached. RCs in 10 mM potassium phosphate buffer, pH 7.3/0.05% lauryldimethylamine-N-oxide (LDAO)/0.2 mM sodium ascorbate, were flowed through either a 2-or a 4-mm pathlength cell and maintained at 100C. Measurements on the microseconds/ milliseconds time scale were performed on an apparatus with 10-ns flashes (11), using static samples held in a 1-cm cuvette at room temperature. No degradation of RCs during the measurements was observed, as judged by ground-stat...

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Section: Discussionmentioning

confidence: 99%

Electron transfer in a genetically modified bacterial reaction center containing a heterodimer.

Kirmaier

Holten

Bylina

et al. 1988

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

114

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“…sphaeroides and Rps. viridis, including other recent spectral simulations [19,20], linear dichroism measurements [21] and the effects of temperature [22] and NaBH4 treatment [23] on the ground state absorption spectrum.…”

Section: Absorption Spectrum Of Pmentioning

confidence: 99%

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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“…The present set of compound should thus provide an excellent testing ground for electronic structure calculations on porphyrins, which have been carried out by numerous groups (principally using semiempirical methods) in order to investigate the photosynthetic reaction center (Eccles et al 1988, Fischer and Scherer 1987, Hanson 1988b, Hanson et al 1987a, 1987b, 1988a, Michel-Beyerle et al 1988, 1988. Accurate calculations should reproduce our results for the gable dimers and provide a superior description of the fiat dimers.…”

Section: Resultsmentioning

confidence: 73%

“…A superior procedure would involve utilizing vibronic models for the monomers and calculating the aggregate lineshape without parameter adjustment; we have employed such an approach in modeling optical spectra from the photosynthetic reaction center (Won and Friesner 1988a). We plan to apply this method to the present problem in future studies.…”

Section: Aggregate Lineshape Calculationsmentioning

confidence: 99%

Exciton interactions in synthetic porphyrin dimers

et al. 1989

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The Soret absorption spectra of six synthetic rigid porphyrin dimers whose crystal structures have been determined are simulated using simple exciton theory. The objective is to test the validity of the point dipole and associated approximations; the electronic interaction parameters are thus calculated using data obtained from the monomer spectra, with no adjustable parameters. Satisfactory agreement between theory and experiment is obtained for one class of dimers but not for a second. This poses a challenge for semiempirical electronic structure methods as to whether improvements over the point dipole calculations can be obtained.

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Simulation of optical spectra from the reaction center of Rhodopseudomonas viridis

Cited by 61 publications

References 0 publications

Electron transfer in a genetically modified bacterial reaction center containing a heterodimer.

Electron transfer in a genetically modified bacterial reaction center containing a heterodimer.

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

Exciton interactions in synthetic porphyrin dimers

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