Bio-Rad DC™ Protein Assay - Manual (Page 3)

Section 1
Introduction and Principle
The Bio-Rad DC Protein Assay is a colorimetric assay for protein concen-
tration following detergent solubilization. The reaction is similar to the well-doc-
umented Lowry
1 assay, but with the following improvements: The reaction
reaches 90% of its maximum color development within 15 minutes thereby
saving valuable time, and the color changes not more than 5% in 1 hour or 10%
in 2 hours after the addition of reagents.
The assay is based on the reaction of protein with an alkaline copper tartrate
solution and Folin reagent. As with the Lowry assay, there are two steps which
lead to color development: The reaction between protein and copper in an alkaline
medium, and the subsequent reduction of Folin reagent by the copper-treated pro-
tein.
1 Color development is primarily due to the amino acids tyrosine and trypto-
phan, and to a lesser extent, cystine, cysteine, and histidine. 1,2 Proteins effect a
reduction of the Folin reagent by loss of 1, 2, or 3 oxygen atoms, thereby produc-
ing one or more of several possible reduced species which have a characteristic blue
color with maximum absorbance at 750 nm and minimum absorbance at 405 nm.
2
Section 2
Product Description
Reagent package (catalog number 500-0116) includes:
250 ml REAGENT A, an alkaline copper tartrate solution
2000 ml REAGENT B, a dilute Folin Reagent
5 ml REAGENT S
(Sufficient for 500 standard assays or 10,000 microplate assays)
The reagent package may be purchased as a kit with a bovine gamma glob-
ulin standard (kit catalog number 500-0111) or bovine serum albumin standard
(kit catalog number 500-0112).
Section 3
Materials Required but Not Supplied
For standard assay:
13 x 100 mm test tubes
Reservoir for working reagent (size depends on amount of reagent that
will be prepared)
Pipets accurately delivering 100 µl, 500 µl, and 4.0 ml
Graduated cylinders or pipets for reagent preparation
Spectrophotometer set to 750 nm
1
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