  Different types of ligands compete in binding to polymers with different
consequences for the physical and chemical properties of the resulting complex.
Here, we derive a general kinetic model for the competitive binding kinetics of
different types of ligands to a linear polymer, using the McGhee and von Hippel
detailed binding site counting procedure. The derived model allows the
description of the competitive binding process in terms of the size of the
ligand, binding and release rates, and cooperativity parameters. We illustrate
the implications of the general theory showing the equations for the
competitive binding of two ligands. The size of the ligand, given by the number
of monomers occluded, is shown to have a great impact in competitive binding.
Ligands requiring a large available gap for binding are strongly inhibited by
smaller ligands. Ligand size then has a leading role compared to binding
affinity or cooperativity. For ligands that can bind in different modes (i.e.,
different number of monomers), this implies that they are more effective in
covering or passivating the polymer in lower modes, if the different modes have
similar binding energies.
