Marina T Kapoustina

Publications (2)3.65 Total impact

• Source

  Available from: ncbi.nlm.nih.gov

  Article: Self-regulation phenomena applied to bacterial reaction centers: 2. Nonequilibrium adiabatic potential: dark and light conformations revisited.

  Alexander O Goushcha, Anthony J Manzo, Gary W Scott, Leonid N Christophorov, Peter P Knox, Yuri M Barabash, Marina T Kapoustina, Natalja M Berezetska, Valery N Kharkyanen
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  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.
  Biophysical Journal 02/2003; 84(2 Pt 1):1146-60. · 3.65 Impact Factor
• Article: Nonlinear Dynamic Processes in an Ensemble of Photosynthetic Reaction Centers. Theory and Experiment

  Alexander O. Goushcha, Marina T. Kapoustina, Valery N. Kharkyanen, Alfred R. Holzwarth
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  ABSTRACT: The results of a theoretical study of the dynamic self-organization phenomenon in the photosynthetic reaction center (RC) from purple bacteria are presented accounting for the stochastic effects an RC ensembles. The adiabatic approximation is applied to determine the specific role of slow structural (protein/cofactors) modes in the correlated behavior of the electronic and structural variables. It is shown that, at certain values of light intensity, the system undergoes bifurcation. The bistability region for the generalized structural variable occurs where the system has two stable states, one characteristic for the dark-adapted sample (i.e., the sample under very low illumination intensity) and the other for the light-adapted sample. The description is based on the solution of the “forward” Kolmogorov equations using the Markov approach. A distribution function describing the probability of finding the electron localized on a particular cofactor with a certain value of the generalized structural variable is used. Modeling shows a good agreement with the results of experimental investigations of transient optical absorbance changes of the isolated RCs from the purple bacterium Rhodobacter sphaeroides. The results indicate that the free energy difference between QA- and QB- changes substantially in different conformational states of the protein/cofactors induced by light over a wide range of the illuminating light intensity.
  09/1997;