Steroids and the practical aspects of performing binding studies.

Many cellular regulatory processes are described by ligand interactions with macromolecules. Steroid complexing with specific cytoplasmic receptor proteins and the subsequent binding of these complexes to nuclear constituents are two such processes which are fundamental to the understanding of steroid hormone action. These reactions are characterized by the binding parameters k, the equilibrium association constant, and M₀, the binding site molarity. The current methods used to determine these two parameters are discussed in relation to the general theory of binding parameter measurement. A number of practical aspects of binding parameter measurement are considered. These include problems encountered by working at dilute non-uniform protein concentrations, non-specific binding, and the limitations of all such experimental systems. An exact solution to the non-linear Scatchard plot is presented for the case when only two non-interacting classes of binding sites need be considered. Finally, a set of specific conclusions is offered which should enable investigators to obtain the most accurate information possible whenever carrying out steroid hormone or receptor binding studies.