Binding isotherms and the interaction between proflavine and a DNA of high G · C content

Binding isotherms corresponding to several situations of ligand binding to a linear polymer are calculated, including cases of cooperativity or anticooperativity between the bound ligand states, multiple binding modes that are competitive or non competitive, and possible exclusion of an arbitrary number of adjacent sites upon occupancy of a site by a single ligand. The sequence generating function method of Lifson and Bradley is used, requiring the assumption that no end effects are involved. The case of strong binding of the dye proflavine to a DNA of high G. C content, that of M. lysodeikticus, is considered in detail, and a single model capable of reconciling the available kinetic and equilibrium data on this system, involving two competing binding modes, is discussed.