85 Bistable regime of adsorption of ligands on a macromolecule induced by an external noise

Abstract

Practically in all experimental and theoretical works dedicated to the interaction of ligands with the macromolecule (DNA, RNA), the investigations are carried out at the fixed parameters of the external medium, that is at the absence of an external noise, though it is obvious that the external noise is never exactly equal to zero. Note also that a number of experimental and theoretical studies have shown that under the action of an external noise, the behavior of a physicochemical system can greatly differ from that of a system in a deterministic medium. Issuing from this fact, the influence of the external noise has been investigated on the adsorption of ligands on a macromolecule. We consider the case of small fillings. The kinetics of adsorption of ligands on a macromolecule are considered in complex with the change of the structure of the adsorption center, which is the profile deformation of the potential energy of the adsorption center at entering of a ligand into the adsorption center. The description of the deformation of the potential energy of the adsorption center is carried out within the framework of the relaxation equation for the conformation variable. Thus, the kinetics of the adsorption of ligands on a macromolecule are described by a set of two nonlinear differential equations, which describes the self-consistent process of adsorption and variation of the conformation variable at each adsorption center. Through the reduction of the system, only a relaxation equation is left allowing to calculate the conformation potential and determine the isotherm of the adsorption of ligands on the macromolecule at the presence of the external noise. It is shown that the stochastic potential strongly depends on the intensity of the external noise. The analysis of the stochastic potential reveals that in some region of changing of the intensity of the external noise, the stochastic potential has two minima separated by a maximum. This leads to a bistable regime of adsorption of ligands on the macromolecule and the S-form of the isotherm of adsorption.