VPB 112: General Veterinary Biochemistry (1+1)

EXERCISE-14: COLOR REACTIONS OF PROTEINS

Biuret test

• The color reactions of proteins are due to the presence of peptide bonds and alkyl / aryl groups.
• This is a general test for compounds having peptide bonds.

Principle

• Alkaline copper sulphate reacts with compounds containing two or more peptide bonds.
• A violet color is produced due to formation of co-ordination complex of cupric ions with the unshared electron pairs of peptide nitrogen and oxygen of water.

Procedure

• To 2 mL of protein solution add 1 mL of 5% NaOH and 1 to 2 drops of 1% copper sulphate.
• Production of violet color indicates the presence of peptide bonds in proteins.
• Amino acids will give negative results.