the encyclopedic entry of Coomassie

Coomassie

Coomassie dyes (also known as Coomassie Brilliant Dyes) are a family of dyes commonly used to stain proteins in sodium dodecyl sulfate and blue native polyacrylamide gel electrophoresis (SDS-PAGE and BN-PAGE, respectively) gels. The gels are soaked in dye and excess stain is then eluted with a solvent ("destaining"). This treatment allows the visualization of protein bands. The gel usually contains a set of molecular weight marker (proteins of pre-determined weight) so that protein molecular weight can be estimated in an unknown solution during the visualization.

Alternatively, Coomassie may be added to undenatured protein in PAGE in place of SDS, in a technique called BN-PAGE; both SDS and CBB have the effect of imparting a net negative charge upon the proteins. Without the Coomassie, the technique is known as CN-PAGE (colorless native), and will only separate negatively-charged proteins.

Variations

The original Coomassie dye was developed as a wool dye and named to commemorate the 1896 British occupation of Coommassie (now Kumasi) in Ghana. The first of the Coomassie series was Coommassie Blue R-250 ("R" standing for "reddish" and "250" being the dye strength indicator). Coommassie Blue G-250 ("G" for "greenish") and Coomassie Violet R-150 later followed. The most commonly used dyes in the laboratory for staining PAGE gels are Coomassie Blue R-250 and G-250. Although G-250 is more sensitive, R-250 affords better resolution, and is often used instead. Shown at right is Coomassie Blue G-250. The structure for Coommassie Blue R-250 is shown Coomassie Brilliant Blue R-250.svg .

Laboratory usage

Coomassie dyes are an integral component of the Bradford Method for determining protein concentration in a solution. The Coomassie dyes binds to proteins via physisorption to arginine, the aromatic amino acids, and histidine. When Coomassie Brilliant Blue G-250 binds to proteins in acid solution, it has an absorbance shift from 465 nm to 595 nm. The absorbance data can then be used in Beer's law to determine protein concentration and ultimately the actual amount of protein in a given solution.