Biorad Protein Concentrations

OPUS cjones at opal.tufts.edu
Thu Mar 10 17:28:00 EST 1994


In article <2li8bu$n2a at mserv1.dl.ac.uk>, LYNDON at BMS-UNIT.ICR.AC.UK writes...
>Can anybody make any reccomendations for a standard protein for the Biorad
>protein assay .... Ig G and BSA seem to vary significantly from one another
>in terms of absorbtion at a given concentration. Are there any rules such
>as use protein x if your sample contain n number of whatever residues??
>The Biorad assay seems to be extensively used but very inaccurate! I know I
>could determine the molar absorbtion coeff. but I do not have enough protein to
>do this.

i use the biorad assay in the microplate format all the time, it does a good
job if you make very sure that you are in the linear range of the assay (about
2-200 ug/ml BSA) it took some playing to get the exact range for my protein.
i don't believe there are any rules except get something that is similar to the 
protein of interest.  
 you can calculate the approximate molar extinction coeff from the predicted
sequence. the actual coeff depends greatly on the folding of the protein (if
the trp or phe is hidden inside the protein for example).

if you are desperate, microsequencing will also give you the inital
concentration

good luck

peace


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