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The reagent is commonly used in the biuret protein assay, a colorimetric test used to determine protein concentration by UV/VIS spectroscopy at wavelength 540 nm. High sensitivity variants of the biuret test
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.
The method combines the reactions of copper ions with the peptide bonds under alkaline conditions (the Biuret test) with the oxidation of aromatic protein residues. The Lowry method is based on the reaction of Cu +, produced by the oxidation of peptide bonds, with Folin–Ciocalteu reagent (a mixture of phosphotungstic acid and phosphomolybdic acid in the Folin–Ciocalteu reaction).
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 ...
While it is possible to analyze these proteins individually, total protein is a relatively quick and inexpensive analysis that does not discriminate by protein type. The traditional method for measuring total protein uses the biuret reagent , but other chemical methods such as dye-binding and refractometry are now available.
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.
This reagent is distinct from Folin's reagent, which is used to detect amines and sulfur-containing compounds. A 1951 paper entitled "Protein measurement with the Folin phenol reagent" [ 5 ] was the most cited paper in the 1945–1988 Science Citation Index , with 187,652 citations.