Reverse staining of sodium dodecyl sulfate polyacrylamide gels by imidazole-zinc salts: sensitive detection of unmodified proteins.

We report here a modification to copper and zinc chloride staining methods. The introduction of a preincubation of the gels, prior to metal staining, with 0.2 M imidazole allows the formation of a homogeneous background for the subsequent precipitation of the metal chelate. The reported imidazole-zinc staining takes minutes, resulting in reproducible staining patterns with only slightly lower sensitivity than silver staining. The method allows efficient recovery of proteins from previously stained gels and is compatible with immunoidentification on Western blots and also with amino acid analysis and NH2-terminal sequence analysis of transferred proteins. A mechanism is proposed to explain the observed improvement in reproducibility and sensitivity of imidazole preincubation to zinc staining.