Escape probability and trapping mechanism in purple bacteria: revisited

Autor(en): Bernhardt, K
Trissl, HW
Stichwörter: Biochemistry & Molecular Biology; Biophysics; CHARGE SEPARATION; EXCITATION-ENERGY TRANSFER; FEMTOSECOND SPECTROSCOPY; fluorescence decay kinetics; fluorescence excitation spectrum; fluorescence yield; LIGHT-HARVESTING ANTENNA; modeling; PHOTOSYNTHETIC REACTION CENTERS; PRIMARY ELECTRON-TRANSFER; RHODOBACTER-SPHAEROIDES; RHODOPSEUDOMONAS-VIRIDIS; RHODOSPIRILLUM-RUBRUM; trapping mechanism; WILD-TYPE
Erscheinungsdatum: 2000
Herausgeber: ELSEVIER
Journal: BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS
Volumen: 1457
Ausgabe: 1-2
Startseite: 1
Seitenende: 17
Zusammenfassung: 
Despite intensive research for decades, the trapping mechanism in the core complex of purple bacteria is still under discussion. In this article, it is attempted to derive a conceptionally simple model that is consistent with all basic experimental observations and that allows definite conclusions on the trapping mechanism. Some experimental data reported in the literature are conflicting or incomplete. Therefore we repeated two already published experiments like the time-resolved fluorescence decay in LH1-only purple bacteria Rhodospirillum rubrum and Rhodopseudomonas viridis chromatophores with open and closed (Q(A)(-)) reaction centers. Furthermore, we measured fluorescence excitation spectra for both species under the two redox-conditions. These data, all measured at room temperature, were analyzed by a target analysis based on a three-state model (antenna, primary donor, and radical pair). All states were allowed to react reversibly and their decay channels were taken into consideration. This leads to seven rate constants to be determined. It turns out that a unique set of numerical values of these rate constants can be found, when further experimental constraints are met simultaneously, i.e, the ratio of the fluorescence yields in the open and closed (Q(A)(-)) states F-m/F-o approximate to 2 and the P+H--recombination kinetics of 3-6 ns. The model allows to define and to quantify escape probabilities and the transfer equilibrium. We conclude that trapping in LH1-only purple bacteria is largely transfer-to-the-trap-limited. Furthermore, the model predicts properties of the reaction center (RC) in its native LH1-environment. Within the framework of our model, the predicted P+H--recombination kinetics are nearly indistinguishable for a hypothetically isolated IPC and an antenna-RC complex, which is in contrast to published experimental data for physically isolated RCs. Therefore RC preparations may display modified kinetic properties. Elsevier Science B.V. All rights reserved.
ISSN: 00052728
DOI: 10.1016/S0005-2728(99)00103-6

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