The bicinchoninic acid (BCA) protein assay, a colorimetric assay for the estimation of protein concentration, is affordable and highly sensitive. It is compatible with a wide range of ionic and nonionic detergents and is highly sensitive with a linear range of 20 to 2000 µg/ml. The assay relies primarily on two reactions. First, the peptide bonds in the protein sample reduce Cu²⁺ ions to Cu⁺. Then, two molecules of bicinchoninic acid (BCA) chelate with each Cu⁺ ion, forming a purple-colored product that readily absorbs light at a wavelength of 562 nm. Because the amount of Cu²⁺ reduced in the first reaction is proportional to the amount of protein present in the solution, the amount of protein present in a solution can be quantified by measuring the absorption spectra and comparing protein solutions with known concentrations. The bicinchoninic acid (BCA) protein assay is suitable for quantifying protein solutions in 1-ml assays or in microwells. It is available in two sizes sufficient for 500 1-ml assays/2500 microassays or 1000 1-ml assays/5000 microassays.
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