Center for Modeling Biological Systems and Data Analysis, Department of Functional Sciences, “Victor Babeș” University of Medicine and Pharmacy Timișoara, 2–4, Eftimie Murgu square, 300041 Timișoara, Romania
The active transport of ions builds and maintains electrochemical potential gradients across biological cell membranes. It is performed by ion pumps: membrane proteins fueled by energy-releasing processes. The stochastic energization-relaxation channel (SERC) model of active transport describes the pump as a multi-ion channel with two conformations, termed energized and relaxed, of specific free energy profiles. Here we present a new, analytic formulation of the SERC model, based on differentiation formulae from the theory of stochastic differential equations. The energization/relaxation switches are described in terms of a Markovian dichotomous noise. Upon averaging the kinetic equations over the noise, the mean ion flux per pump molecule is obtained as a function of time. Its asymptotic value, the stationary ion flux generated by one transport protein, is a measurable quantity, found to be in qualitative agreement with experimental results on bacteriorhodopsin, a light-driven proton pump.
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