DC Protein Assay Kit From Bio-Rad

The DC Protein Assay Kit by Bio-Rad is used for the detection and quantification of protein following detergent solubilization. The detection is via a colorimetric assay similar to the Lowry assay, whereby a two-step reaction yields a color change that occurs in the presence of amide bonds. The entire procedure from start to finish takes no longer than 30 minutes and should always be performed at room temperature.

The advantage of using this kit is that it is compatible with detergents, a limitation of the traditional Lowry assay. In addition, the reaction reaches 90% of its maximum color development within 15 minutes, which is quicker than some other assays I’ve seen. The color changes less than 5% in 1 hour, making the reaction extremely stable for accurate measurements.

The kit is compatible with many detergents including 10% SDC, 1% Triton X-100, and 0.05% Sodium Azide, 1mM DTT and many more (see manufacturer’s online brochure). However, it is imperative that standards always be prepared in the same buffer as the sample. Protein standards can vary in their readout, so it is critical to ensure reproducibility to use the same protein standard (BSA, gamma globulin, etc.) each time you create a standard curve. The standards are not included in the kit, but can be purchased separately from Bio-Rad.

The kit includes an alkaline copper tartrate solution (reagent A), a dilute Folin Reagent (Reagent B), and protein assay reagent S. Before performing the assay, a working reagent A’ must be created by diluting 20 ul of reagent S into every 1 ml of reagent A. This A’ is stable for one week. Protein standards must be created containing protein ranging from 0.2 mg/ml to 1.5 mg/ml. The reaction is very easy: Simply add reagent A’ to sample and vortex. Then, add reagent B and vortex immediately. A color change should occur. Incubate 15 minutes and then read absorbance at 750 nm in a spectrophotometer or microplate reader. Create a standard curve with your protein standards, and then calculate the protein concentration of sample based on this curve. We have cut the recommended volumes by ¼, so we can read samples in standard spectrophotometer cuvettes and this works just fine, plus it saves reagent. We have successfully used this kit in yeast protein quantification after detergent solubilization in 10% SDS.

I have found that this kit works well and gives highly reproducible results. It is especially nice for working with membrane bound proteins. The price isn’t too bad, with a kit costing around $120, which is enough for approximately 500 standard assays or 10,000 microplate assays. Reagents, when stored out of direct sun light at room temperature, are good for 6 months from date of purchase.

I would happily recommend this kit.