An exact general analysis of ligand binding displacement and saturation curves.

Quantitative analysis of a ligand-protein interaction relates binding to the free concentration of ligand molecules in solution. A theoretical analysis is presented herein, by which intermolecular interactions can be described as a function of the added concentrations of ligand molecules. Following this analysis, ligand binding displacement and saturation curves can be converted directly into a linear form, even when nonradioactively labeled ligands are used to detect the ligand-protein interaction. From the linearities obtained, relevant binding parameters, including the binding dissociation constant, can be calculated. On the basis of this analysis, binding parameters have been characterized for the interaction between biotin-protein A and immunoglobulins, using ELISA-type detection, and for the interaction of a fluorescently labeled fatty acid with a specific fatty acid binding protein.