title: Self-regulation phenomena applied to bacterial reaction centers: 2. Nonequilibrium adiabatic potential: dark and light conformations revisited.
abstract: Experimental and theoretical results in support of nonlinear dynamic behavior of photosynthetic reaction centers under light-activated conditions are presented. Different conditions of light adaptation allow for preparation of reaction centers in either of two different conformational states. These states were detected both by short actinic flashes and by the switching of the actinic illumination level between different stationary state values. In the second method, the equilibration kinetics of reaction centers isolated from Rhodobacter sphaeroides were shown to be inherently biphasic. The fast and slow equilibration kinetics are shown to correspond to electron transfer (charge separation) at a fixed structure and to combined electron-conformational transitions governed by the bounded diffusion along the potential surface, respectively. The primary donor recovery kinetics after an actinic flash revealed a pronounced dependence on the time interval (deltat) between cessation of a lengthy preillumination of a sample and the actinic flash. A pronounced slow relaxation component with a decay half time of more than 50 s was measured for deltat > 10 s. This component corresponds to charge recombination in reaction centers for which light-induced structural changes have not relaxed completely before the flash. The amplitude of this component depended on the conditions of the sample preparation, specifically on the type of detergent used in the preparation. The redox potential parameters as well as the structural diffusion constants were estimated for samples prepared in different ways.
authors.affiliation: Department of Chemistry, University of California/Riverside, Riverside, California, USA.
authors.forename: Alexander O
authors.initials: AO
authors.lastname: Goushcha
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Manzo
authors.forename: Gary W
authors.initials: GW
authors.lastname: Scott
authors.forename: Leonid N
authors.initials: LN
authors.lastname: Christophorov
authors.forename: Peter P
authors.initials: PP
authors.lastname: Knox
authors.forename: Yuri M
authors.initials: YM
authors.lastname: Barabash
authors.forename: Marina T
authors.initials: MT
authors.lastname: Kapoustina
authors.forename: Natalja M
authors.initials: NM
authors.lastname: Berezetska
authors.forename: Valery N
authors.initials: VN
authors.lastname: Kharkyanen
mesh_terms: D000222:Adaptation, Physiological; D003624:Darkness; D003902:Detergents / Q000737:chemistry*; D006706:Homeostasis; D007700:Kinetics; D008027:Light; D046911:Macromolecular Substances; D008956:Models, Chemical; D008958:Models, Molecular; D017711:Nonlinear Dynamics; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000528:radiation effects*; D011487:Protein Conformation / Q000528:radiation effects; D016992:Rhodobacter / Q000737:chemistry / Q000145:classification; D013045:Species Specificity
chemical_list: D003902:Detergents; D046911:Macromolecular Substances; D045322:Photosynthetic Reaction Center Complex Proteins