Biuret reagent

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The Biuret reagent is made of sodium hydroxide and copper (II) sulfate. The blue reagent turns violet in the presence of proteins, and changes to pink when combined with short-chain polypeptides. The sodium hydroxide does not participate in the reaction at all, but is merely there to provide an alkaline medium so that the reaction can take place. The principle can be demonstrated with the chemical compound biuret which, just as proteins, is able to complexate copper (II) ions.

The reagent is commonly used in a biuret protein assay, a colorimetric assay used to determine protein concentration.

The biuret assay does not in fact use biuret (biuret is a compound formed from two urea molecules), but is thus named as it detects the peptide bond between the urea molecules or between amino acids. It is best read at 550nm after a 20 minute incubation period at room temperature. As the absorption read is a relative value, not an absolute, a standard curve is required to quantify protein/peptide content.

[edit] The Biuret Test

Main Article: Biuret test

Not all biuret tests actually require the biuret reagent. Rather, the phrase "biuret test" is a generic term for the testing of proteins by using copper (II) sulfate solution in an alkaline environment. Thus, the process of testing for proteins in a solution by first adding a small amount of sodium hydroxide, and then adding copper (II) sulfate drop by drop, is also known as a biuret test.

[edit] References

[edit] See Also

• Biuret test
• Biuret