Bio-Rad Protein Assay - Manual (Page 13)

11
6. Is any sample preparation required?
In general, no. However, the protein must be solubilized. (The sample
can not be a suspension or an unfiltered homogenate.)
7. Can protein bound to a solid phase be quantitated?
Yes, according to a recent reference in Analytical Biochemistry.
Consult Anal. Biochem. 200, 195 (1992) for additional information.
8. What is the shelf life of the dye reagent concentrate and the standards?
The Dye Reagent Concentrate is stable for 1 year. For optimum shelf
life, store at 4 ˚C.
Lyophilized preparations of Protein Standard I (bovine gamma globu-
lin) and Protein Standard II (bovine serum albumin), if included,
should be refrigerated upon arrival. These lyophilized preparations
have a shelf life of 1 year at 4 ˚C. Rehydrated and stored at 4 ˚C, the
protein solutions should be used within 60 days. Rehydrated and stored
in aliquots at -20 ˚C, the protein solutions should be used within 5
years. Avoid repeated freeze and thaw cycles of the protein standard.
9. Does the binding of the blue dye to cuvettes skew results?
The amount of dye that binds to cuvettes, especially quartz cuvettes,
is negligible.
1 Therefore, removal of the residual blue color between
each sample reading is unnecessary. However, since the cuvettes may
be used for subsequent procedures, there are several recommended
treatments for dye removal:
(a) Rinse cuvette with methanol, or
(b) Rinse cuvette with concentrated glassware detergent, fol-
lowed by DDI water, then acetone, or
(c) Soak cuvette in 0.1 N HCl for a few hours, then wash as in
(b).
Bio-Rad's disposable polystyrene cuvettes (catalog number 223-9950)
are recommended for the protein assay. They absorb less blue dye
than glass cuvettes, and the cuvettes can be used as the mixing vessels
for the standard assay if sample and reagent volumes are reduced to
50 µl and 2.50 ml, respectively. This technique eliminates the need for
test tubes, and yields twice as many assays per bottle of reagent.
LIT33C 8/31/98 02:25 PM Page 11