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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.
BCA protein assay in a 96 well plate. The bicinchoninic acid assay (BCA assay), also known as the Smith assay, after its inventor, Paul K. Smith at the Pierce Chemical Company, [1] now part of Thermo Fisher Scientific, is a biochemical assay for determining the total concentration of protein in a solution (0.5 μg/mL to 1.5 mg/mL), similar to Lowry protein assay, Bradford protein assay or ...
The biuret test is a chemical test for proteins and polypeptides. It is based on the biuret reagent, a blue solution that turns violet upon contact with proteins, or any substance with peptide bonds. The test and reagent do not actually contain biuret; they are so named because both biuret and proteins have the same response to the test.
Bicinchoninic acid is most commonly employed in the bicinchoninic acid (BCA) assay, which is used to determine the total concentration of protein in a solution. Bicinchoninic acid is used to detect the presence of cuprous ions, due to its purple coloration via a biuret reaction.
A similar colorimetric assay, the Bicinchoninic acid assay, uses a chemical reaction to determine protein concentration. The Biuret assay utilizes a biuret reagent which turns purple in the presence of proteins due to the chelation of copper salts in an alkaline solution. [4]
It is a common precipitant in protein crystallography and is also an ingredient in the Biuret reagent which is used to measure protein concentration. This ingredient maintains cupric ions in solution at an alkaline pH.
The rate of a reaction is the concentration of substrate disappearing (or product produced) per unit time (mol L −1 s −1). The % purity is 100% × (specific activity of enzyme sample / specific activity of pure enzyme). The impure sample has lower specific activity because some of the mass is not actually enzyme.
Biuret Test Derived Assays: Bicinchoninic acid assay (BCA assay): Detection down to 0.5 μg/mL; Lowry Protein assay: Detection in the range of 0.01–1.0 mg/mL; Fluorescamine: Quantifies proteins and peptides in solution if primary amine are present in the amino acids; Amido black: Detection in the range of 1-12 μg/mL