A biological interpretation of transient anomalous subdiffusion. II. Reaction kinetics

¹ University of California - Davis

^* To whom correspondence should be addressed. E-mail: mjsaxton{at}ucdavis.edu.

Submitted on May 31, 2007
Revised on July 24, 2007
Accepted on 14 September 2007

	Abstract

Reaction kinetics in a cell or cell membrane are modeled in terms of the first passage time for a random walker at a random initial position to reach an immobile target site in the presence of a hierarchy of nonreactive binding sites. Monte Carlo calculations are carried out for the triangular, square, and cubic lattices. The mean capture time is expressed as the product of three factors: the analytical expression of Montroll for the capture time in a system with a single target and no binding sites; an exact expression for the mean escape time from the set of lattice points; and a correction factor for the number of targets present. The correction factor, obtained from Monte Carlo calculations, is between one and two. Trapping may contribute significantly to noise in reaction rates. The statistical distribution of capture times is obtained from Monte Carlo calculations and shows a crossover from power-law to exponential behavior. The distribution is analyzed using probability generating functions; this analysis resolves the contributions of the different sources of randomness to the distribution of capture times. This analysis predicts the distribution function for a lattice with perfect mixing; deviations reflect imperfect mixing in an ordinary random walk.

Key Words: anomalous subdiffusion, kinetics, membranes, noise in biological reactions, nucleus, random walk