Applications in Biochemistry
Coomassie Brilliant Blue R-250 was first used to visualise proteins in 1963 by Fazekas de St. Groth and colleagues. Protein samples were separated electrophoretically on a cellulose acetate sheet. The sheet was then soaked in sulfosalicylic acid to fix the protein bands and then transferred to a solution of the dye.
Two years later in 1965 Meyer and Lambert used Coomassie Brilliant Blue R-250 to stain protein samples after electrophoretic separation in a polyacrylamide gel. They soaked the gel in a dye solution containing methanol, acetic acid and water. As the dye stained the polyacrylamide gel as well as the protein, to visualise the protein bands they needed to destain the gel which they did electrophoretically. Subsequent publications reported that polyacrylamide gels could be successfully destained using an acetic acid solution.
The first report of the use of the "G" form of the dye to visualise protein bands in polyacrylamide gels came in 1967, where the dye was dissolved in an acetic acid solution containing methanol. It was subsequently discovered that the protein bands could be stained without staining the polyacrylamide by using a colloid of the "G" form of the dye in a trichloroacetic acid solution containing no methanol. Using this procedure it was no longer necessary to destain the gel. Modern formulations typically use a colloid of the "G" form of dye in a solution containing phosphoric acid, ethanol (or methanol) and ammonium sulfate (or aluminium sulfate).
The Bradford assay uses the spectral properties of Coomassie Brilliant Blue G-250 to estimate the amount of protein in a solution. A protein sample is added to a solution of the dye in phosphoric acid and ethanol. Under the acid conditions the dye is normally a brownish colour but on binding to the protein the blue form of the dye is produced. The optical absorbance of the solution is measured at a wavelength of 595 nm.
On binding to a protein the negatively charged Coomassie Brilliant Blue G-250 dye molecule will give an overall negative charge to the protein. This property can be used to separate proteins or protein complexes using polyacrylamide gel electrophoresis under non-denaturing conditions in a technique called Blue Native PAGE. The mobility of the complex in the polyacrylamide gel will depend on both the size of the protein complex (i.e. the molecular weight) and on the amount of dye bound to the protein.
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