Time-resolved spectroscopy of the primary photosynthetic processes of membrane-bound reaction centers from an antenna-deficient mutant of Rhodobacter capsulatus

Schmidt, Stefan; Arlt, T.; Hamm, Peter; Lauterwasser, Christoph; Finkele, Ulrich; Drews, Gerhart

doi:10.1016/0005-2728(93)90124-x

Cited by 35 publications

(38 citation statements)

References 18 publications

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“…The discrepancy in lifetimes (0.9 and 1.5 ps, cf. 1.9 ps in the present study) is possibly attributable to the reduction of Q A in our studies, but not in the experiments described in (6,12,18). The overall decay of P* was also found to slow down upon quinone reduction (7,19).…”

Section: Target Analysis Of the Wt Rc Data With A Reaction Scheme Invcontrasting

confidence: 72%

“…The most favourable fit to the full set of experimental data from 690-1060 nm required five lifetimes. A combination of the model for RC kinetics from (5,6,8,9,12,18) and the idea of radical pair relaxation (5,18,(38)(39)(40) gave a five-component kinetic scheme ( Figure 5) that offered a satisfactory description of the data. The SADS of the two excited states and three radical pair states involved in this scheme were consistent with what is known about the spectra of these states.…”

Section: Implications Of Our Findings For the Mechanism Of Primary Chmentioning

confidence: 99%

“…The second mechanism involves the formation of the radical pair P + B L -as a discrete, but short-lived, intermediate in a two-step reaction from P* to P + H L -. The complexity of the optical changes accompanying primary electron transfer has lent much support to the idea that such intermediate charge separated states play a role in the reaction, and direct evidence for the formation of the P + B L -radical pair state has been presented (6,8,9,12,18,21,22).…”

mentioning

confidence: 99%

“…Experiments have shown that the lifetime of P* is approximately 3.5 ps in detergent-solubilized RCs (4) and approximately 4.5 ps in membrane-bound RCs (6,7). Time-resolved difference absorption spectroscopy can be used to follow the sequence of events in the first steps of transmembrane electron transfer.…”

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confidence: 99%

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Primary Electron Transfer Kinetics in Membrane-Bound Rhodobacter sphaeroides Reaction Centers: A Global and Target Analysis

et al. 1997

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Absorbance difference kinetics were measured on quinone-reduced membrane-bound wild type Rhodobacter sphaeroides reaction centers in the wavelength region from 690 to 1060 nm using 800 nm excitation. Global analysis of the data revealed five lifetimes of 0.18, 1.9, 5.1, and 22 ps and a long-lived component for the processes that underlie the spectral evolution of the system. The 0.18 ps component was ascribed to energy transfer from the excited state of the accessory bacteriochlorophyll (B*) to the primary donor (P*). The 1.9 ps component was associated with a state involving a BChl anion absorbing in the 1020 nm region. This led to the conclusion that primary electron transfer is best described by a model in which the electron is passed from P* to the acceptor bacteriopheophytin (H L ) via the monomeric bacteriochlorophyll (B L ), with the formation of the radical pair state P + B L-. An analysis assuming partial direct charge separation from B* [Van Brederode, M. E., Jones, M. R., and Chem. Phys. Lett. 268,[143][144][145][146][147][148][149] was also consistent with the data. Within the framework of a five component model, the 5.1 and 22 ps lifetimes were associated with charge separation and relaxation of the P + H L -radical pair state respectively, providing a description which adequately accounted for the complex kinetics of decay of P*. Alternatively, by assuming that the 5.1 and 22 ps components originate from a single component with a multi-exponential decay, a simpler analysis with only four components could be employed, resulting in only a small increase (7%) in the weighted root mean square error of the fit. In both descriptions part of the decay of P* proceeds with a lifetime of about 2 ps. The relative merits of these alternative descriptions of the primary events in light-driven electron transfer are discussed. Similar measurements on YM210H mutant reaction centers revealed four lifetimes of 0.2, 3.1, and 12 ps and a long-lived component. The 3.1 and 12 ps lifetimes are ascribed to multi-exponential decay of the P* state. The differences with the WT data are discussed.The reaction center (RC) of purple bacteria is responsible for the conversion of light energy into a transmembrane electrical potential. The structures of the RC from two species of purple bacteria, Rhodopseudomonas (Rps.) Viridis and Rhodobacter (Rb.) sphaeroides, have been solved to high resolution (1, 2). They reveal an assembly of protein subunits and redox cofactors that are arranged around an axis of approximate 2-fold symmetry. The primary donor of electrons (P) is a pair of excitonically-coupled bacteriochloropyll a (BChl) molecules positioned close to the periplasmic face of the protein. The remaining redox cofactors, two monomeric BChls (B), two molecules of bacteriopheophytin a (H), and two ubiquinones (Q), are arranged around the symmetry axis in two branches that span the membrane dielectric. Excitation of P initiates a sequence of electron transfer reactions that result in the separation of charge across the ...

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Section: Target Analysis Of the Wt Rc Data With A Reaction Scheme Invcontrasting

confidence: 72%

Section: Implications Of Our Findings For the Mechanism Of Primary Chmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Primary Electron Transfer Kinetics in Membrane-Bound Rhodobacter sphaeroides Reaction Centers: A Global and Target Analysis

et al. 1997

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“…The transient absorption data were obtained with a sub-picosecond laser system operating at 50 Hz (Dressier et al 1991, Schmidt et al 1993. The sample was held in a 1 mm cuvette with an optical density of about 0.5 at 870 nm.…”

Section: Methodsmentioning

confidence: 99%

Spectroscopic characterization of reaction centers of the (M)Y210W mutant of the photosynthetic bacterium Rhodobacter sphaeroides

et al. 1994

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The tyrosine-(M)210 of the reaction center of Rhodobacter sphaeroides 2.4.1 has been changed to a tryptophan using site-directed mutagenesis. The reaction center of this mutant has been characterized by low-temperature absorption and fluorescence spectroscopy, time-resolved sub-picosecond spectroscopy, and magnetic resonance spectroscopy. The charge separation process showed bi-exponential kinetics at room temperature, with a main time constant of 36 ps and an additional fast time constant of 5.1 ps. Temperature dependent fluorescence measurements predict that the lifetime of P* becomes 4-5 times slower at cryogenic temperatures. From EPR and absorbance-detected magnetic resonance (ADMR, LD-ADMR) we conclude that the dimeric structure of P is not significantly changed upon mutation. In contrast, the interaction of the accessory bacteriochlorophyll B A with its environment appears to be altered, possibly because of a change in its position.

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Electron Transfer—from Isolated Molecules to Biomolecules

Bixon¹,

Jortner²

1999

Advances in Chemical Physics

480

346

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Time-resolved spectroscopy of the primary photosynthetic processes of membrane-bound reaction centers from an antenna-deficient mutant of Rhodobacter capsulatus

Cited by 35 publications

References 18 publications

Primary Electron Transfer Kinetics in Membrane-Bound Rhodobacter sphaeroides Reaction Centers: A Global and Target Analysis

Primary Electron Transfer Kinetics in Membrane-Bound Rhodobacter sphaeroides Reaction Centers: A Global and Target Analysis

Spectroscopic characterization of reaction centers of the (M)Y210W mutant of the photosynthetic bacterium Rhodobacter sphaeroides

Electron Transfer—from Isolated Molecules to Biomolecules

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