Characterization of binding equilibrium data by a variety of fitted isotherms.

Experimental binding equilibrium data, resulting from measurement of ligand binding to macromolecular carriers, are usually described by fitting of binding constants. These constants are often highly variable, as illustrated in the present paper by two examples, binding of salicylate to human serum albumin and of oxygen to hemoglobin. In order to avoid over-interpretation of binding constants it is pointed out that the best-fit solution, obtained by least-squares fitting, may be supplemented by several, e.g. thirty, acceptable solutions. It is further shown how the 30 sets of acceptable binding constants, plotted as Klotz' affinity profiles, can serve for evaluation of cooperative effects.