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- Title
Mechanism by which a single water molecule affects primary charge separation kinetics in a bacterial photosynthetic reaction center of Rhodobacter sphaeroides.
- Authors
Ivashin, N.; Shchupak, E.
- Abstract
Using quantum-chemical methods, we have studied the role played by water molecules W-A and W-B that are bound by hydrogen bonds to accessory bacteriochlorophyll molecules B and B in the process of primary charge separation in the reaction center of Rhodobacter Sphaeroides. We have found that the occurrence of a rotational mode of the W-A molecule at 32 cm and/or its harmonics in stimulated emission of an electron donor P* and the dynamics of population of the states PB and PH may be related to the structural heterogeneity of the reaction center and the existence of a conformation in which the W-A molecule is predominantly involved in one hydrogen bond (with B A). Based on the calculated redox potentials B and P, it has been shown that the appearance of the W-A molecule in the reaction center reduces the energy of the PB state by ∼600 cm. This is somewhat smaller than the influence of the amino-acid residue Tyr (∼870 cm) and correlates well with a substantial decrease in the electron transfer rate in mutant forms of reaction centers GM203L (which do not contain W-A molecules) and YM210F (in which Tyr is replaced with Phe). The data obtained allow us to suggest that rotation of the water molecule with a fixed position of its H atom that is involved in a hydrogen bond with the keto carbonyl group of B is initiated due to the charge separation between the halves of special pair P and the formation of the state PP. The large effect of this rotation on the kinetics of population of the states PB and PH after the excitation of P is quite consistent with its influence on the energy of the state PB.
- Subjects
WATER analysis; MOLECULES; SEPARATION (Technology); PHOTOSYNTHETIC reaction centers; RHODOBACTER sphaeroides; HYDROGEN bonding; CHARGE exchange; BACTERIA
- Publication
Optics & Spectroscopy, 2012, Vol 113, Issue 5, p474
- ISSN
0030-400X
- Publication type
Article
- DOI
10.1134/S0030400X1209007X