Further consideration of systematic errors present in protein-ligand interactions

Relatively minor systematic errors present during measurements of protein-ligand interaction can lead to large inaccuracies in the calculated values of the equilibrium dissociation constant and the total concentration of the binding protein. These errors, which include binding of the ligand to low affinity material and underestimation of bound ligand, cause the calculation of the concentration of free ligand at equilibrium to be overestimated. We report herein a model of ligand-protein binding which incorporates these errors into the mathematical formulation of the equilibrium binding equation. The effect of these errors on the Scatchard plot is presented.