The Bio-Rad protein assay is a simple colorimetric assay for measuring total protein concentration and is based on the Bradford dye-binding method (Bradford 1976). Using standard procedure, the assay is used with samples having protein concentrations between 200 and 1,400 µg/ml (20–140 µg total). It is easy to adapt the assay from the standard-concentration range to a low-concentration (<25 µg/ml; 1–20 µg total) microassay or for rapid determinations in 96-well microplates.
The Bio-Rad protein assay is:
- Based on the color change of Coomassie brilliant blue G-250 dye in response to various concentrations of protein — the dye binds to primarily basic (especially arginine) and aromatic amino acid residues
- Useful for measuring proteins and polypeptides, depending on the charged groups, with molecular weights >3,000–5,000
Many detergents and basic protein buffers interfere with the assay; interference may be caused by chemical-protein or chemical-dye interactions. Refer to the list of compatible reagents for more information.
Bio-Rad protein assay kits offer either bovine serum albumin or bovine γ-globulin standards.
Bradford MM (1976). A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem 72. 248–254.