Interactions between Coomassie Blue Dye and DNA in the Bradford Assay

The Bradford Assay is well known for its ability to detect and quantify protein in solution with a great degree of sensitivity. During the assay, Coomassie Blue dye is allowed to bind to the protein for a carefully measured period of time, and then the samples are analyzed by visible spectrophotometry. Construction of a standard curve reveals an extinction coefficient that correlates absorbance of light at 595 nm with the concentration of protein in the test solution. For relatively pure protein solutions, the correlation is excellent and consistent however, presence of nucleic acids in a crude protein preparation has potential for interference. Interactions between Coomassie Blue Dye (G‐250) and DNA from salmon testes during the Bradford Assay were characterized. It was found that Coomassie Blue G‐250 in Bradford Assay reagent does interact with DNA at approximately one‐fifteenth the rate of the interactions with standard bovine serum albumin.