A simple sensitive method, applicable to small polypeptides, for the determination of proteins in polyacrylamide gels after isoelectric focusing

A simple method is described for the determination of polypeptides and proteins in polyacrylamide gels after isoelectric focusing. Precipitates formed in trichloroacetic acid, under controlled conditions, are quantified densitometrically by measuring the proportion of light scattered. The procedure is of particular value in its applicability to smaller polypeptides, with mol.wts. of 3000-6000, which are not fixed adequately in gels by other procedures currently in use. The working range, over which polypeptide concentration is proportional to the effective absorbance, is approx. 1-30 microgram per component.