title: Nuclear wave packet motion between P* and P(+)B(A)(-) potential surfaces with a subsequent electron transfer to H(A) in bacterial reaction centers at 90 K. Electron transfer pathway.
abstract: In Rhodobacter sphaeroides R-26 reaction centers (RCs) the nuclear wave packet induced by 25 fs excitation at 90 K moves on the primary electron donor P* potential energy hypersurface with initial frequency at approximately 130 cm(-1) (monitored by stimulated emission measurement). At the long-wavelength side of P* stimulated emission at 935 nm the wave packet is transferred to the surface with P(+)B(A)(-) character at 120, 380, 1.2 fs, etc. delays (monitored by measurement of the primary electron acceptor B(A)(-) band at 1020 nm). However, only beginning from 380 fs delay and later the relative stabilization of the state P(+)B(A)(-) is observed. This is accompanied by the electron transfer to bacteriopheophytin H(A) (monitored by H(A) band measurement at 760 nm). The most active mode of 32 cm(-1) in the electron transfer and its overtones up to the seventh were found in the Fourier transform spectrum of the oscillatory part of the kinetics of the P* stimulated emission and of the P(+)B(A)(-) and P(+)H(A)(-) formation. This mode and its overtones are apparently populated via the 130 cm(-1) vibrational mode. The deuteration of the sample shifts the fundamental frequency (32 cm(-1)) and all overtones by the same factor of approximately 1.3. This mode and its overtones are suppressed by a factor of approximately 4.7 in the dry film of RCs. The results obtained indicate that the 32 cm(-1) mode might be related to a rotation of hydrogen-containing groups (possibly the water molecule) participating in the modulation of the primary electron transfer from P* to B(A)(-) in at least 35% of RCs. The Brookhaven Protein Data Bank (1PRC) displays the water molecule located at the position HOH302 between His M200 (axial ligand for P(B)) and the oxygen of ring V of B(A) which might be a part (approximately 35%) of the molecular pathway for electron transfer from P* to B(A).
authors.affiliation: Department of Photobiophysics, Belozersky Institute of Chemical and Physical Biology, Moscow State University, Moscow 119992, Russia.
authors.forename: Andrei G
authors.initials: AG
authors.lastname: Yakovlev
authors.forename: Anatoli Ya
authors.initials: AY
authors.lastname: Shkuropatov
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Shuvalov
mesh_terms: D000595:Amino Acid Sequence; D003624:Darkness; D004579:Electron Transport; D007700:Kinetics; D008027:Light; D008958:Models, Molecular; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins