ABSTRACT
The aim of the work is to analyze the response of a biomolecule to an external influence based on the study of its hidden states by identifying differential equations with constant coefficients. The relevance of the work lies in the fact that often the main reaction of an object to an external action can be represented as a sum of various exponential functions with a common starting point and a material balance equation. In this case, the response of an object to an external action corresponds to a system of differential equations with constant coefficients. This character of the main reaction may be due to the influence of the hidden properties of the object, which play the role of regulatory parameters. The problem is that the hidden factors and the system of differential equations are not identified. As an object, isolated reaction centers (RC) of the bacteria Rhodobacter sphaeroides , which possess the above properties, has used. Their structure is well studied. As result of studying of photo excitation processes of the reaction center has shown that electron transfer kinetics (the main reaction) can be approximated by three normalized exponential functions. Program was developed to identify for four differential equations of electron transfer and the balance equation, the behavior of hidden states of the reaction center. It was concluded that time the dependence the probability density of finding an electron in different conformational states of the reaction center characterizes the space-time changes in the structure of the reaction center.
ABSTRACT
The present work is related to the investigation of slow kinetics of electron transport in the reaction centers (RCs) of Rhodobacter sphaeroides. Experimental data on the absorption kinetics of aqueous solutions of reaction centers at different modes of photoexcitation are given. It is shown that the kinetics of oxidation and reduction of RCs are well described by the sum of three exponential functions. This allows to suggest a two-level kinetic model for electron transport in the RC as a system of four electron-conformational states which correspond to three balance differential equations combined with state equation. The solution of inverse problem made it possible to obtain the rate constant values in kinetic equations for different times and intensities of exciting light. Analysis of rate constant values in different modes of RC excitation allowed to suggest that two mechanisms of structural changes are involved in RC photo-oxidation. One mechanism leads to the increment of the rate of electron return, another one-to its drop. Structural changes were found out to occur in the RCs under incident light. After light was turned off, the reduction of RCs was determined by the second mechanism.
