NONLINEAR DYNAMIC PROCESSES IN AN ENSEMBLE OF PHOTOSYNTHETIC REACTIONCENTERS - THEORY AND EXPERIMENT

The results of a theoretical study of the dynamic self-organization ph enomenon in the photosynthetic reaction center (RC) from purple bacter ia are presented accounting for the stochastic effects an RC ensembles . The adiabatic approximation is applied to determine the specific rol e of slow structural (protein/cofactors) modes in the correlated behav ior of the electronic and structural variables, it is shown that, at c ertain values of light intensity, the system undergoes bifurcation. Th e bistability region for the generalized structural variable occurs wh ere the system has two stable stales, 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 Mar kov approach, A distribution function describing the probability of fi nding the electron localized on a particular cofactor with a certain v alue of the generalized structural variable is used. Modeling shows a good agreement with the results of experimental investigations of tran sient optical absorbance changes of the isolated RCs from the purple b acterium Rhodobacter sphaeroides. The results indicate that the free e nergy difference between Q(A)(-) and Q(B)(-) changes substantially in different conformational states of the protein/cofactors induced by li ght over a wide range of the illuminating light intensity.