Photoelectric currents across planar bilayer membranes containing bacterial reaction centers. Response under conditions of single electron turnover

Packham, Nigel K.; Dutton, P. Leslie; Müeller, Paul

doi:10.1016/s0006-3495(82)84693-6

Cited by 47 publications

(6 citation statements)

References 27 publications

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“…Both quinones are present in the R. sphaeroides structure with the iron located between the two. The lack of an observed transmembrane potential associated with the electron transfer from QX to QB (25)(26)(27) suggested that the line joining the two quinones lies in the plane of the membrane; this is in agreement with the postulate that the 2-fold symmetry axis observed in the structure is perpendicular to the plane of the membrane (5,6). That the iron is approximately equidistant from both quinones was suggested from an analysis of EPR data (28).…”

Section: Resultssupporting

confidence: 57%

Structural homology of reaction centers from Rhodopseudomonas sphaeroides and Rhodopseudomonas viridis as determined by x-ray diffraction.

Allen¹,

Fehér²,

Yeates³

et al. 1986

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

347

165

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Crystals of the reaction center (RC) from RCs from purple photosynthetic bacteria contain three subunits, L, M, and H (present in a 1:1:1 stoichiometry) and a number of cofactors: four bacteriochlorophylls (BChls), two bacteriopheophytins, two quinones, QA (primary electron acceptor), and QB (secondary electron acceptor), and one nonheme iron (for reviews, see refs. 1 and 2). Although RCs from different species exhibit many similarities in structure, there are some significant structural differences.The RCs from Rhodopseudomonas sphaeroides and Rhodopseudomonas viridis that are the subject of this investigation show the following differences. In R. sphaeroides the secondary, water-soluble cytochrome is not present in purified RCs. In contrast, RCs from R. viridis contain a fourth subunit, a cytochrome, that has four heme groups associated with it. The two species contain different types of BChl: R. sphaeroides has BChl-a whereas R. viridis contains BChl-b. The primary quinone in R. sphaeroides is a ubiquinone, whereas in R. viridis it is a menaquinone. Furthermore, the two quinones that serve as acceptors are retained in purified RCs from R. sphaeroides, but one is apparently lost from R. viridis during the purification.Although extensive work has been done during the past two decades to characterize RCs, until recently there was very little information available on their three-dimensional structure. The reason was the lack of crystals suitable for x-ray diffraction studies. This situation changed with the successful crystallization of RCs from R. viridis (3) and R. sphaeroides (4, §). These crystals are of sufficient size and quality to obtain good x-ray diffraction data. The structure of the RCs from R. viridis has been reported recently at a resolution of 3 A (5, 6).In this work we describe the use of the Patterson search (molecular replacement) method (for reviews, see refs. 7 and 8) to obtain a low-resolution electron density map of the RC from R. sphaeroides and to show the homology between the structures of the RCs from the two bacterial species. A preliminary account of this work has been presented (9).EXPERIMENTAL PROCEDURES Crystallization. The RC from R. sphaeroides was crystallized by using the vapor diffusion technique. Different crystallization conditions produced a variety of forms as reported (4,10,11). The crystal form used for these structural studies was grown under the following conditions. The initial protein solution consisted of 5 mg of RC per ml, 0.36 M NaCl, 3.9%

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Section: Resultssupporting

confidence: 57%

Structural homology of reaction centers from Rhodopseudomonas sphaeroides and Rhodopseudomonas viridis as determined by x-ray diffraction.

Allen¹,

Fehér²,

Yeates³

et al. 1986

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

347

165

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“…Electron transfers between cofactors of the RC are in general accompanied by a potential difference (i.e., an electrogenicity) across the membrane (19)(20)(21)(22). An exception to this is the electron transfer from QA to QB (21,23,24). The lack of electrogenicity for this step can be explained by assuming that the electron path is parallel to the membrane surface.…”

Section: Resultsmentioning

confidence: 99%

Structure of the reaction center from Rhodobacter sphaeroides R-26: protein-cofactor (quinones and Fe2+) interactions.

Allen

Fehér

Yeates

et al. 1988

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

339

306

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The three-dimensional structure of the reaction center (RC) from Rhodobacter sphaeroides has been determined by x-ray diffraction to a resolution of 2.8 A with an R value of 24%. The interactions of the protein with the primary quinone, QA, secondary quinone, QB and the nonheme iron are described and compared to those of RCs from Rhodopseudomonas viridis. Structural differences between the QA and QB environments that contribute to the function of the quinones (the electron transfer from QA to QB and the charge recombination of Q-, Q-with the primary donor) are delineated. The protein residues that may be involved in the protonation of QB are identified. A pathway for the doubly reduced QB to dissociate from the RC is proposed. The interactions between QB and the residues that have been changed in herbicide-resistant mutants are described. The environment of the nonheme iron is compared to the environments of metal ions in other proteins.The reaction center (RC) is a protein-pigment complex that mediates the primary photochemistry of photosynthetic systems. The RC from Rhodobacter sphaeroides R-26 is composed of three protein subunits (L, M, and H) and several cofactors (for a review, see ref. 1). Serving as electron acceptors are the primary quinone QA and the secondary quinone QB. In Rb. sphaeroides both quinones are ubiquinones, whereas in Rhodopseudomonas viridis QA is a menaquinone and QB is a ubiquinone.The three-dimensional structure of the RC from Rb. sphaeroides R-26 has been obtained to a resolution of2.8 A (2-4) and an R value of 24%. In this paper, we describe the interactions of the protein with the quinones and the nonheme iron. We emphasize structural features that appear to be important in electron and proton transfer. Differences in the interactions of the protein with the quinones in Rb. sphaeroides and Rps. viridis are described, although a detailed comparison between the QB interactions is difficult because of the low occupancy of the QB sites in crystals ofRps. viridis (5, 6). The interactions with the nonheme iron are found to be very similar for the two bacterial species. The interactions ofthe protein with the other cofactors as well as the crystallographic procedures have been reported (7). In a subsequent paper (8), the asymmetries ofthe two branches of the cofactors and a comparison of RCs from different species will be presented. RESULTSThe Primary Quinone. The primary quinone, QAI is located near the cytoplasmic side of the RC. Its position and orientation are well defined by the electron density, although there is no steric hindrance to moving the quinone to a position indicated by the dotted line in Fig. 1 (see below). The normal of the quinone ring forms an angle of =60°with respect to the membrane normal as defined by the direction of the twofold symmetry axis (4). QA interacts with the amino acid residues of the D, de, and E helices of the M subunit (3) (see Fig. 1).The two carbonyl oxygens Of QA are within hydrogenbonding distance to the peptide nitrogen of Ala M260 and ...

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“…We have used cyt c2+ to reduce D+ in those RCs whose donors point towards the compartment into which the cyt c2+ had been added (16). Other workers have used Fe (CN)63to selectively oxidize D (17,20). Fig.…”

Section: The Basic Photoresponse In Functionally Oriented Rcsmentioning

confidence: 99%

“…A variety of approaches have been developed to monitor electrical events associated with light induced electron transfer in both chromatophores and reconstituted RClipid systems (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). Direct measurements (with microelectrodes) of light induced electric currents and potentials in chromatophores have, thus far, not been reported.…”

Section: Introductionmentioning

confidence: 99%

“…Direct measurements (with microelectrodes) of light induced electric currents and potentials in chromatophores have, thus far, not been reported. However, such direct measurements have recently been reported in systems of purified RCs incorporated in planar lipid bilayers (16,17,20,22). These studies demonstrate directly the transduction by RCs of light energy into electric currents and have shown that the electron transfer steps from D to QA and from cyt c2+ to D+ are electrogenic.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The effect of an applied electric field on the charge recombination kinetics in reaction centers reconstituted in planar lipid bilayers

Gopher¹,

Blatt²,

Schönfeld³

et al. 1985

Biophysical Journal

109

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Reaction Centers (RCs) from the photosynthetic bacterium Rhodopseudomonas sphaeroides were incorporated in planar bilayers made from monolayers derived from liposomes reconstituted with purified RCs. The photocurrents associated with the charge recombination process between the reduced primary quinone (QA-) and the oxidized bacteriochlorophyll donor (D+) were measured as a function of voltage (-150 mV less than V less than 150 mV) applied across the bilayer. When QA was the native ubiquinone (UQ) the charge recombination was voltage independent. However, when UQ was replaced by anthraquinone (AQ), the recombination time depended on the applied voltage V according to the relation tau = 8.5 X 10(-3) eV/0.175S. These results were explained by a simple model in which the charge recombination from UQ- proceeds directly to D+ while that from AQ occurs via a thermally activated intermediate state, D+I-QA, where I is the intermediate acceptor. The voltage dependence arises from an electric field induced change in the energy gap, delta G0, between the states D+I-QA and D+IQA-. This model is supported by the measured temperature dependence of the charge recombination time, which for RCs with AQ gave a value of delta G0 = 340 +/- 20 meV. In contrast, delta G0 for RCs with UQ as the primary acceptor, is sufficiently large (approximately 550 meV) so that even in the presence of the field, the direct pathway dominates. The voltage dependence shows that the electron transfer from I- to QA is electrogenic. From a quantitative analysis of the voltage dependence on the recombination rate it was concluded that the component of the distance between I and QA along the normal to the membrane is about one-seventh of the thickness of the membrane. This implies that the electron transfer from I to Q contributes at least one-seventh to the potential generated by the charge separation between D+ and QA-.

show abstract

Photoelectric currents across planar bilayer membranes containing bacterial reaction centers. Response under conditions of single electron turnover

Cited by 47 publications

References 27 publications

Structural homology of reaction centers from Rhodopseudomonas sphaeroides and Rhodopseudomonas viridis as determined by x-ray diffraction.

Structural homology of reaction centers from Rhodopseudomonas sphaeroides and Rhodopseudomonas viridis as determined by x-ray diffraction.

Structure of the reaction center from Rhodobacter sphaeroides R-26: protein-cofactor (quinones and Fe2+) interactions.

The effect of an applied electric field on the charge recombination kinetics in reaction centers reconstituted in planar lipid bilayers

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