Biuret Test to Detect the Presence of Peptide Bonds
Biuret Test
Biuret Test
• Biuret Test is a chemical test used to show/detect the presence of peptide bonds, which are the basis for the formation of proteins. Explanation
In the presence of peptides, copper (II) ion forms a violet-colored coordination complexes in an alkaline solution. This test can be used to asses the concentration of protein because peptide bonds occur with the same frequency per amino acid in the peptide.
According to Beer-Lambert Law, the intensity of the color and hence the absorption at 540 nm is directly proportional to the protein concentation.
Procedures
• Mix 1ml of egg white solution and 10 drops of
NaOH in the test tube.
• Add 1 drop of CuSO4 solution. Mix well and record your observation.
• Dissolve one tablet of aspartame or ½ sachet of
Equal in 2 ml of water.
• Add to the resulting solution 10 drops of NaOH and
CuSO4 solution.
• Mix well and record your observation. Compare the two results.
What Is the principle involved in the biuret test? The Biuret Test is based on the reduction of Cu2+ to Cu+ which then complexes with the nitrogen atoms on the peptide bonds. Which it is form a violet-colored (chelate complex) with peptide bonds in alkaline solution.
Cont.
•
•
•
Lone electron pairs from 4 nitrogen atoms in the peptide bond coordinate a copper (II) ion.
A chelate complex is formed, the complex absorbs light at 540 nm so appears violet.
Hence a color changes from blue to violet indicate that proteins are present. The greater concentration of peptide bonds, the greater color intensity. If the concentration of peptide is low, the short-chain peptide are present which the blue color will turn to pink.
OBSERVATIONS and INTERPRETATION
OBSERVATION
• No change (solution remains blue )
• The solution turns from blue to violet
(deep purple)
• The solution turns from blue to pink
INTERPRETATION
• Proteins are not present
• Proteins are present
• Peptides are present
(Peptides or peptones are short chains of amino acid
Biuret Test
• Biuret Test is a chemical test used to show/detect the presence of peptide bonds, which are the basis for the formation of proteins. Explanation
In the presence of peptides, copper (II) ion forms a violet-colored coordination complexes in an alkaline solution. This test can be used to asses the concentration of protein because peptide bonds occur with the same frequency per amino acid in the peptide.
According to Beer-Lambert Law, the intensity of the color and hence the absorption at 540 nm is directly proportional to the protein concentation.
Procedures
• Mix 1ml of egg white solution and 10 drops of
NaOH in the test tube.
• Add 1 drop of CuSO4 solution. Mix well and record your observation.
• Dissolve one tablet of aspartame or ½ sachet of
Equal in 2 ml of water.
• Add to the resulting solution 10 drops of NaOH and
CuSO4 solution.
• Mix well and record your observation. Compare the two results.
What Is the principle involved in the biuret test? The Biuret Test is based on the reduction of Cu2+ to Cu+ which then complexes with the nitrogen atoms on the peptide bonds. Which it is form a violet-colored (chelate complex) with peptide bonds in alkaline solution.
Cont.
•
•
•
Lone electron pairs from 4 nitrogen atoms in the peptide bond coordinate a copper (II) ion.
A chelate complex is formed, the complex absorbs light at 540 nm so appears violet.
Hence a color changes from blue to violet indicate that proteins are present. The greater concentration of peptide bonds, the greater color intensity. If the concentration of peptide is low, the short-chain peptide are present which the blue color will turn to pink.
OBSERVATIONS and INTERPRETATION
OBSERVATION
• No change (solution remains blue )
• The solution turns from blue to violet
(deep purple)
• The solution turns from blue to pink
INTERPRETATION
• Proteins are not present
• Proteins are present
• Peptides are present
(Peptides or peptones are short chains of amino acid