[show abstract][hide abstract] ABSTRACT: Time-resolved cw EPR measurements of the Rhodobacter (Rb) sphaeroides R-26 reaction center primary donor triplet state excited with plane-polarised light are reported. The pigment composition of the reaction center was chemically modified, so that the bacteriopheophytin molecule in the cofactor branch which is inactive towards electron transfer was replaced by plant pheophytin a. This enabled selective excitation of the bacteriopheophytin and pheophytin molecules, and provided conditions for a high-quality magnetophotoselection study. For the first time, orientation of the Qy optical transition dipole moment relative to the molecular frame of the bacteriopheophytin in the active cofactor branch is determined. Of the four orientations allowed by magnetophotoselection, one was chosen as the most plausible. The corresponding Qy vector is tilted from the bacteriopheophytin tetrapyrrole plane by 15°, and projects onto this plane almost on the y-molecular axis. It is suggested that the deviation of the vector from the molecular plane results from an interaction of bacteriopheophytin with the neighbouring molecule of accessory bacteriochlorophyll.
Chemical Physics 01/2003; 294(3):451-458. · 1.96 Impact Factor
[show abstract][hide abstract] ABSTRACT: Two g = 2.0 spin-polarized ESR signals with different properties are detected in native and QA-substituted reaction centers from R. sphaeroides R-26. The signal from substituted RCs is attributed to the primary donor cation radical. Native RCs demonstrate a signal with strong temperature dependence which most likely arises from spin-correlated radical pair P+−Q−AFe2+.
Biochimica Et Biophysica Acta-bioenergetics - BBA-BIOENERGETICS. 01/1993; 1142:207-210.
[show abstract][hide abstract] ABSTRACT: The fine structure of the absorption band of P in reaction centers of various phototrophic bacteria has been studied at 1.7–70 K. The vibronic structure with a characteristic frequency of ∼ 140 cm−1, zero-phonon line and phonon wing for the 0-0 transition with relatively weak coupling parameters have been resolved.
[show abstract][hide abstract] ABSTRACT: Burning of spectral holes within the absorption band of the primary electron donor P in reaction centers of Rhodopseudomonas viridis is studied using selective excitation at 1014 nm and 1.7 K. A narrow (≤ 1.0 cm−1) spectral hole with relatively weak electron-phonon and vibronic coupling is burned if the intermediary electron acceptor I is pre-reduced. The hole is broadened up to ∼90–150 cm−1 if I is neutral and the electron-transfer chain is open. Broadening of the hole is discussed in terms of the fast (∼70–110 fs) electron hopping between P* and P+BL− (BL, bacteriochlorophyll monomer in L protein subunit).
[show abstract][hide abstract] ABSTRACT: Femtosecond measurements of kinetics and spectra of absorbance changes (ΔA) were carried out with modified reaction centers (RCs) from Rhodobacter sphaeroides (R-26) from which nonactive bacteriochlorophyll BM (located in the M protein subunit) was removed. The band of BM at 800 nm in native RCs is shifted in femtosecond measurements and obscures the ΔA of active bacteriochlorophyll BL (L subunit). The spectrum of ΔA in modified RCs at 6 ps delay includes the bleachings of the bands of P (primary electron donor) at 870 nm, of BL at 805 nm and of HL (bacteriopheophytin located in the L subunit) at 755 nm showing the reduction of 0̃.5 mol BL and 0̃.5 mol HL per mol P+. These data confirm an earlier suggestion that BL participates as an electron acceptor in the light-induced primary charge separation and agree with recent X-ray analysis of Rhodopseudomonas viridis and R. sphaeroides RCs which shows a location of BL between P and HL.
Febs Letters - FEBS LETT. 01/1987; 216(2):245-248.