[36] Gel-staining techniques

Naturally colored proteins, such as myoglobin, hemoglobin, ferritin, and cytochrome c may be directly observed in gels illuminated with light in the visual spectrum, providing that their chromophores are not damaged during electrophoresis. If one is primarily interested in detection of abundant proteins and not concerned with the determination of purity or the detection of trace proteins, the Coomassie Blue stains may be useful. Coomassie Blue staining requires an acidic medium for the generation of an electrostatic attraction between the dye molecules and the amino groups of the proteins. This ionic attraction, together with van der Waals forces, binds the dye–protein complex together. Coomassie Blue stains exhibit three times the staining intensity of Fast Green stain and six times the intensity of Amido Black stain. The staining intensities of these dyes are approximately proportional to their relative molar absorption coefficients. There is no need to remove the remaining unreacted stain reagent as it is not fluorescent and it degrades rapidly in water. It also does not interfere with the electrophoretic separation of the labeled proteins.