Characterization of the interaction constants for the binding of two unlabelled ligands to the sites of a receptor. An experimental strategy.

The model describing the binding of three ligands to the sites of a receptor is theoretically studied in order to characterize the binding interaction between two unlabelled ligands. For this, the binding of a third labelled ligand, the affinity of which is dependent on the presence of the unlabelled ligands, must be measured in different conditions. This paper describes an experimental strategy leading to an accurate determination of the equilibrium parameters of the model. This strategy, which assumes that the model is compatible with the data, rests on the determination of the optimal experimental conditions, i.e. the choice of the ligand concentrations which minimize the error of the parameter estimates. For this purpose, a computer program which runs on a microcomputer under the MS-DOS operating system has been elaborated on the basis of the D-optimization criterion. This work shows that such a computer analysis is essential to the determination of the optimal experimental design, even when very simple biochemical systems are considered.