ABSTRACT

A wide range of techniques exist to determine protein concentration, spectroscopically. The Bradford assay is one of the oldest, most reliable, and least expensive ways to determine protein concentration. It is rapid, and easy to do with a standard visible wavelength spectrophotometer. Protein samples are not pure at all, and to determine the protein concentration in mg/mL, a standard curve is made with a known protein such as albumin. It is assumed that on average all proteins would have the same proportion of absorbing residues relative to their mass, and so a milligram of any protein would absorb the same as a milligram of albumin. A protein that was lacking absorbing residues might be very abundant, but would not absorb very well. Bicinchionic Acid (BCA) is a copper-based organic dye, which complexes to peptide bonds. The worst difficulty with the method is that BCA reagent is both expensive and unstable.