Protein quantitation based on bicinchoninic acid (BCA) is simple, sensitive, and tolerant to many detergents and substances known to interfere with the Lowry method. However, certain compounds often used during protein purification do interfere with the BCA protein assay. The response of the BCA chromophore to various interfering substances has provided insight into the mechanism of protein quantitation by BCA. Certain substances (e.g., glucose, mercaptoethanol, and dithiothreitol) elicit a strong absorbance at 562 nm when combined with the BCA working reagent. The absorbance appears to be identical to the normal response elicited by protein. Other agents (e.g., ammonium sulfate and certain ampholytes) diminish the protein-induced color development and shift the wavelength of the color response. Both types of interference can be eliminated by selectively precipitating protein with deoxycholate and trichloroacetic acid (A. Bensadoun and D. Weinstein (1976) Anal. Biochem. 70, 241-250) prior to reaction with bicinchoninic acid. The modifications described here permit quick, efficient removal of many interfering substances that are commonly utilized during protein purification.
Bibliographical noteFunding Information:
by the Hormel Foun- of Minnesota Graduate American Cancer Soci- Additional support was Program Project Grant
Direct support for these studies was provided dation, by a grant-in-aid from the University School, and by the University of Minnesota’s ety Institutional Research Grant Program. provided by Public Health Service HL08214.