All that glisters is not gold: The physical basis of protein coloration in silver-stained gels

The introduction of silver-staining to detect electrophoretically separated proteins in polyacrylamide gels has provided a method that, with the most responsive proteins, is more sensitive by a factor of ∼100 than Coomassie Blue, the most commonly used organic stain. With silver staining, most proteins take on a brownish hue. However, under appropriate conditions, certain proteins have been found to exhibit distinct and vivid colors. Yellow, blue, red and green bands have all been observed. Colorability is a property with considerable analytical potential, in that it may become possible to infer chemical properties of proteins on the basis of their propensities for coloration upon silver-staining. Such information would considerably enhance the analytical capabilities of gel electrophoresis, which for the most part have been restricted to estimates of molecular weights and isoelectric points. To help realize this potential, we have investigated the physical basis of the colorability of proteins.