Despite its acceptance, the traditional Lowry assay has specific disadvantages, such as reagent instability and the requirements for exact timing of reagent addition and mixing to obtain accurate results. Consequently, modifications of the Lowry assay have found their way into the commercially available Lowry-type assay products. Pierce Chemical's Modified Lowry Protein Assay, for example, is based on a modification that replaces two of the traditional Lowry reagents with one stable solution. The result is a stable, preformulated product with nearly 100 percent color response correlation with the original Lowry assay. Capable of functioning in the presence of 1 percent detergent and many other common reagents, the assay requires only a 15-minute incubation period before samples can be read.
Absorbances are stable for at least two hours.
In September, Bio-Rad introduced the RC DC Protein Assay, a colorimetric assay for determining protein concentration in the presence of both reducing agents and detergents. Based on a modification of the Lowry protocol, this new product has all the unique capabilities of the original DC Protein Assay, in addition to covering a broader range of reagents. Sigma-Aldrich of St. Louis offers two modified Lowry assays. The Modified Lowry Kit for Protein Determination is also based on the above-mentioned modification. The kit facilitates lipoprotein dissolution and uses deoxycholate and trichloroacetic acid to precipitate proteins away from interfering substances.