A permanent Zn2+ reverse staining method for the detection and quantification of proteins in polyacrylamide gels.

An optimized method for reverse staining of proteins in polyacrylamide gels is described. The method is based on the selective precipitation of a white imidazole-zinc complex all along the gel except in the protein bands. The high selectivity of this method allows a "toning procedure" which turns the formerly white background into a deep blue, leaving the protein bands transparent and colorless. The chemistry of the whole process is discussed. The toned gels can be dried with no alteration of the stain pattern. Transmittance scanning of these dried gels reveals a linear relationship between the spectroscopical magnitude and the protein concentration in the range 10-100 ng. This relationship is not dependent on the protein nature. This method detects bands corresponding to 5 ng of protein (minimum detectable about 1.4 ng protein/mm2).