The basis for colored silver-protein complex formation in stained polyacrylamide gels.

Using a modified silver stain of Merril et al. [(1981) Science 211, 1437-1438] for staining polypeptides in sodium dodecyl sulfate-polyacrylamide gels, protein bands reproducibly stain different shades of blue, yellow, red, and gray. The procedure is highly temperature dependent, with optimal color formation at 42 degrees C. The procedure may be completed within 2 h. Color formation is due to silver ion complexes with charged amino acid side chains. The color of the silver-protein complex can be predicted if the amino acid sequence is known, although some exceptions are discussed. This provides another dimension to the characterization of proteins by gel electrophoresis.