An Ambiguity in the Variable-Solvent Solubility Test: Homogeneity of β₁-Lactoglobulin

Abstract

IN the variable-solvent solubility test (see, for example, Falconer and Taylor¹, Derrien², Smithies³) a constant amount of protein is brought to a series of different concentrations of a salt, the volume, pH and temperature being constant. The equilibrium concentration of protein remaining in solution is then plotted against the concentration of salt. A single protein is expected to give a curve like that in Fig. 1. Here AB represents the exponential solubility relationship of the protein⁴. Under conditions represented by the horizontal part PQ of the curve (the position of which depends on the amount of protein and the volume chosen) all the protein remains in solution; solid phase first appears at Q where PQ cuts AB, and from this point the curve follows AB as the concentration of salt is increased.