Scatchard plots with a positive slope: dependence upon ligand concentration.

The inverse dependence of binding constants (nK) upon albumin concentration for 2-(4'-hydroxybenzeneazo) benzoic acid (HABA) has been investigated with bovine and human albumin by equilibrium dialysis. Data obtained by the use of a range of concentrations of either bovine or human albumin, together with a single ligand concentration, gave positive Scatchard plots indicative of binding constants inversely dependent upon protein concentration. The slope of each plot was influenced by the particular ligand concentration used and an increase in the ligand concentration in the case of both bovine and human albumin resulted in a decrease in the slope of the positive Scatchard plot. Higher concentrations of ligand produced a transformation from a positive to a negative plot with both bovine and human albumin.