Question

What is the difference between the BCA assay and the Biuret reaction when it comes to protein analysis?

Answer 1

The BCA protein assay is used for quantitation of total protein in a sample. The principle of this method is that proteins can reduce Cu⁺² to Cu⁺¹ in an alkaline solution and result in a purple color formation by bicinchoninic acid.

The biuret test, also known as Piotrowski's test, is a chemical test used for detecting the presence of peptide bonds. In the presence of peptides, a copper ion forms mauve-colored coordination complexes in an alkaline solution. Several variants on the test have been developed, such as the BCA test and the Modified Lowry test.

The biuret reaction can be used to assess the concentration of proteins because peptide bonds occur with the same frequency per amino acid in the peptide. The intensity of the color, and hence the absorption at 540 nm, is directly proportional to the protein concentration, according to the Beer–Lambert law.