Dear Regouat,

Please read the following text:

The Bradford protein assay is a spectroscopic analytical procedure used to measure the concentration of protein in a solution. It is subjective, i.e., dependent on the amino acid composition of the measured protein.

The Bradford assay is linear over a short range, typically from 0 µg/mL to 2000 µg/mL, often making dilutions of a sample necessary before analysis.

It is also inhibited by the presence of detergents.

Much of the non-linearity stems from the equilibrium between two different forms of the dye which is perturbed by adding the protein. The Bradford assay linearizes by measuring the ratio of the absorbances, 595 over 450 nm. This modified Bradford assay is approximately 10 times more sensitive than the conventional one. (Zor & Selinger, 1995).

Alternative protein assays include:

Ultraviolet–visible spectroscopy

Biuret protein assay

Lowry protein assay

BCA protein assay

Amido black protein assay

For more details, please access the following links:

https://en.wikipedia.org/wiki/Bradford_protein_assay

http://www.ruf.rice.edu/~bioslabs/methods/protein/bradford.html

Hoping this will be helpful,

Rafik

The Bradford method is very convenient for measuring the total concentration of protein in an extract, as long as the amount of any interfering substances is not too high. You will need a standard, which is a purified protein solution with a known concentration, such as bovine serum albumin. Here is the product literature for one Bradford assay kit. Many companies sell pre-made Bradford reagents.

http://www.bio-rad.com/LifeScience/pdf/Bulletin_9004.pdf

Other relatively simple assays for total protein are the BCA assay and the Lowry assay, also available as kits.

There is a commercial kit  for protein assays that can be used with interfering detergents and reagents of all types. I no longer do this kind of work, but at one point I had to solve this problem and this kit works.  It of course works even when interference is not an issue. The company is still selling it.  Just tracked it down: http://www.gbiosciences.com/PDF/Protocol/NI_Protein_Assay.pdf