Bio-Rad Protein Assay - Manual (Page 11)

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4. My sample is a mixture of proteins. Which protein standard should I
use to generate the standard curve?
In any protein assay, the best protein to use as a standard is a purified
preparation of the protein being assayed. In the absence of such an
absolute reference protein, one must select another protein as a rela-
tive standard. The best relative standard to use is one which has simi-
lar properties to, and which gives a color yield similar to that of, the
protein(s) being assayed.
Any purified protein can be selected as a reference standard if only
relative protein values are desired. Bio-Rad offers two standards,
Bovine gamma globulin (Standard I, catalog number 500-0005) and
bovine serum albumin (Standard II, catalog number 500-0007).
5. How does the Bio-Rad Protein Assay compare to other assay methods?
The Bio-Rad Protein Assay compares favorably with two other pro-
tein assay methods, the Biuret and the Lowry. In the table below,
results are tabulated from dilutions made to gravimetrically prepared
10 mg/ml solutions of commercially available proteins. Bio-Rad
Protein Standard I (bovine gamma globulin) was used for the Lowry
and Bio-Rad Protein Assays, with bovine serum albumin was used for
the Biuret method. All three assays display considerable variation in
response to different proteins, but the averages were comparable.
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