The effect of cell size and receptor density on ligand-receptor reaction rate constants

Abstract

A method is developed for calculating rate constants for ligands interacting with cell-bound receptors in terms of rate constants for reactions between solubilized molecules. The results indicate that for identical reaction mechanisms and typical cellular and molecular dimensions, the rate and equilibrium constants for reaction of solution phase ligand with receptors that are cell-bound or otherwise fixed, as on a bead, can be several orders of magnitude smaller or larger than their values for reactions with dispersed receptors. These variations have little to do with diffusion coefficient differences, but are intimately connected to the size and density of receptors, and the relation between diffusive and reactive rate constants. The main equations are tabularized and their utility illustrated by a brief discussion of data from the literature.