A. General Protein Color Tests
1. Biuret Test
- chemical test for detecting presence of peptide bonds in the presence of peptides
- Positive visible result: violet
1. Biuret Test
- chemical test for detecting presence of peptide bonds in the presence of peptides
- Positive visible result: violet
(From L to R) 1ml each of 1% egg albumin, 1% glycine, 1% pheylalanine, and distilled water. Each of the solutions were added 1ml 10% sodium hydroxide solution and 10 drops of 0.1% cupric sulfate solution. The violet coloration in the egg albumin solution indicates a positive visible result for the Biuret test.
2. Ninhydrin Test
- shows positive test for alpha amino acids and proteins that contain free amino acid groups
- Positive visible result: deep blue or purple color
- shows positive test for alpha amino acids and proteins that contain free amino acid groups
- Positive visible result: deep blue or purple color
3. Xanthoproteic Test
Xanthoprotein - yellow acid substance formed by the reaction of hot HNO3 on albuminous or protein matter and is changed to a deep orange-yellow color by the addition of NH3
Xanthoprotein - yellow acid substance formed by the reaction of hot HNO3 on albuminous or protein matter and is changed to a deep orange-yellow color by the addition of NH3
B. Color Tests for Specific Amino Acids
1. Millon's Test for Tyrosine
- a test developed by Auguste Millon, a French chemist
- This test is not specific for proteins. It detects phenolic compounds. A reddish-brown coloration or precipitate indicates the presence of tyrosine residue.
1. Millon's Test for Tyrosine
- a test developed by Auguste Millon, a French chemist
- This test is not specific for proteins. It detects phenolic compounds. A reddish-brown coloration or precipitate indicates the presence of tyrosine residue.
2. Hopkins-Cole Test for Tryptophan
- positive visible result: purple ring in the junction where the two liquids meet
- positive visible result: purple ring in the junction where the two liquids meet
3. Sakaguchi test for Arginine
-positive result: red
-positive result: red
4. Lead Acetate test for Labile Sulfur