Roger, While I agree with your list, the BCA assay does not use molybdate (as we make it from scratch with bicinchoninic acid, sodium carbonate, sodium bicarbonate, sodium tartrate, and cupric sulfate pentahydrate). For membrane proteins, I prefer the BCA assay until the protein is pure enough to use A280.
Cheers, Michael **************************************************************** R. Michael Garavito, Ph.D. Professor of Biochemistry & Molecular Biology 603 Wilson Rd., Rm. 513 Michigan State University East Lansing, MI 48824-1319 Office: (517) 355-9724 Lab: (517) 353-9125 FAX: (517) 353-9334 Email: rmgarav...@gmail.com **************************************************************** On Feb 13, 2014, at 10:39 AM, Roger Rowlett <rrowl...@colgate.edu> wrote: > Your basic choices for protein assays are: > Alkaline copper methods (e.g., Biuret and micro-biuret) > alkaline copper + molybdate methods (e.g., Lowry, BCA assays) > Hydrophobic dye methods (e.g. Bradford) > UV methods (e.g., A280, A230, A210, etc.) > Method 1 is least sensitive to amino acid composition, but is also has > highest detection limits. Thiols interfere. Method 2 is very idiosyncratic > with amino acid composition, and also subject to interference by thiols. > Method 3 is not usable in detergent solutions. Method 4 has many inteferences > as most everything absorbs in the far UV region. > If you have some special protein cofactors, metals, chromophores, etc. these > can be exploited for better measurements. For ecample metalloproteins are > easy to quantify by ICP-OES or TXRF if they are reasonably pure. > Cheers, > _______________________________________ > Roger S. Rowlett > Gordon & Dorothy Kline Professor > Department of Chemistry > Colgate University > 13 Oak Drive > Hamilton, NY 13346 > > tel: (315)-228-7245 > ofc: (315)-228-7395 > fax: (315)-228-7935 > email: rrowl...@colgate.edu > On 2/13/2014 10:06 AM, Raji Edayathumangalam wrote: >> Dear CC4BBers, >> >> I am trying to figure out what is the best way to determine the protein >> concentration of my membrane protein. My purified membrane protein is in >> 20mM Tris pH 7, 150mM NaCl and 0.02% DDM (CMC of DDM=0.0076%). >> >> After reading the friendly manuals and searching online, I've learned that >> detergents interferes with assays like Bradford but can't find good >> descriptions of what works best. For now, I am trying to estimate >> concentration from absorbance at 280nm and using molar extinction >> coefficients based on aromatic amino acids, but again suspect detergent >> interference. I would like to know what other folks working on membrane >> proteins are doing. >> >> Thanks very much. >> Raji >> >> -- >> Raji Edayathumangalam >> Instructor in Neurology, Harvard Medical School >> Research Associate, Brigham and Women's Hospital >> Visiting Research Scholar, Brandeis University >> >
