Coomassie Brilliant Blue G-250

Technical Specifications

Product Description & Scientific Applications

Coomassie Brilliant Blue G-250 binds protein through a pH-dependent equilibrium between three forms — cationic, neutral, and anionic. The free dye in acid is predominantly cationic; although the anionic form is not free at the reagent pH, it is the form that complexes with protein. Binding requires an intact macromolecule and acts chiefly through arginine, with smaller contributions from the other basic and aromatic residues, by van der Waals and hydrophobic contacts. The protein–dye complex is insoluble at the moment of measurement, and a protein's solubility and structure in the reagent set how strongly it responds.

Common Scientific Applications

Bradford protein assay. The dye is the basis of the Bradford assay, a rapid and sensitive way to quantify microgram amounts of protein by protein–dye binding. The protein–dye complex absorbs at 595 nm, which gives the colorimetric read-out. Because the signal depends on arginine, lysine, and histidine content, the response differs between proteins, and the assay is calibrated against a chosen protein standard. The neutral dye species, bases, and detergents interfere by displacing the form equilibrium, so the reagent tolerates only limited detergent; solubilising membrane proteins in glucopyranoside detergents brings them within range.

Blue native electrophoresis. In blue native PAGE the dye coats membrane protein complexes solubilised in mild detergent, giving them a negative surface charge so they migrate to the anode and separate by size without denaturation. Whole multiprotein complexes of the oxidative phosphorylation system resolve in one gel and can be extracted in enzymatically active form. A second dimension of SDS-PAGE then resolves each complex into its subunits, and the method also separates intact respiratory supercomplexes and respirasomes, which in-gel activity stains confirm as functional.

Colloidal gel staining. As a colloidal suspension in phosphoric acid, the dye stains protein bands in polyacrylamide gels — SDS-PAGE and isoelectric focusing alike — with low background. In the colloidal "blue silver" form its sensitivity approaches that of silver staining, down to about 1 ng of protein in a band. The dye binds non-covalently, by ionic anchoring to acidic residues followed by hydrophobic association, so stained bands remain intact for downstream mass-spectrometric identification.

Shipping Destinations

• EU & UK: Priority delivery, 2–5 business days.
• United States (DDP): 3–7 business days, duties and taxes prepaid.
• EFTA Countries (DDP): 3–7 business days, duties and taxes prepaid.
• Worldwide: 7–14 business days, selected locations.