On the interpretation of binding isotherms in complex biological systems: Apparent homogeneity of some heterogeneous systems

A simple treatment of the effect of site heterogeneity upon binding isotherms is presented, which is applicable to the analysis of data obtained from measurements of hormone, drug, or lectin binding to membranes and cell surfaces. Using this treatment, isotherms corresponding to various distributions of binding constants have been fitted to examples of experimental binding data ordinarily interpreted in the context of a homogeneous binding site model. It is found that these data do not permit one to exclude the alternate possibility of a broad distribution of the binding constant $\text{K}$. If a homogeneous binding site model can be satisfactorily fitted to the data, it is probable that the value of $\text{K}$ obtained by this procedure is equal or nearly equal to the number average value of $\text{K}$ in the actual (unknown) distribution.