TEST FOR PROTEINS/AMINO ACIDS
NAME (TEST) REAGENTS USED EXPECTED INTERPRETATION
POSITIVE RESULT
1. Millon’s Test Mercurous nitrate in Flesh to red color Due to phenol group
HNO3 contained in tyrosine
2. Biuret Test CuSO4 Rose-pink to violet Due to the presence of
peptide linkage (-CONH2)
3. Hopkins Cole Glyoxylic acid Violet ring Due to the presence of an
Reaction (CHOCOOH), CONC. indole nucleus in the
H2SO4 tryptophan component
4. Xanthoproteic Conc. HNO3, NaOH Yellow to orange Due to the nitration of
Reaction the benzene ring (C6H5)
present in the structure
of such amino acids as
tyrosine, tryptophan and
phenylalanine.
(The yellow stain in the
skin produced by HNO3 is
due to this reaction)
5. Test for SH group NaOH -Splits up the sulfur -For protein containing
to form Na2S cystine, cysteine or
methionine
- due to the formation of
- black ppt. lead sulfide
Lead acetate
6. Lieberman’ s test Conc. HCl, sucrose Violet color Presence of tryptophan
soln.
7. Molisch’s test H2SO4 Violet ring Presence of glycol-protein
develops
8. Ninhydrin Triketohydrindene Blue color Due to the presence of
reaction hydrate the α-amino group in the
molecule except for
proline and
hydroxyproline
9. Sakaguchi Alkaline solution, a- Red color Presence of arginine
reaction naphthol and sodium
hypochlorite
NAME (TEST) REAGENTS USED EXPECTED INTERPRETATION
POSITIVE RESULT
1. Millon’s Test Mercurous nitrate in Flesh to red color Due to phenol group
HNO3 contained in tyrosine
2. Biuret Test CuSO4 Rose-pink to violet Due to the presence of
peptide linkage (-CONH2)
3. Hopkins Cole Glyoxylic acid Violet ring Due to the presence of an
Reaction (CHOCOOH), CONC. indole nucleus in the
H2SO4 tryptophan component
4. Xanthoproteic Conc. HNO3, NaOH Yellow to orange Due to the nitration of
Reaction the benzene ring (C6H5)
present in the structure
of such amino acids as
tyrosine, tryptophan and
phenylalanine.
(The yellow stain in the
skin produced by HNO3 is
due to this reaction)
5. Test for SH group NaOH -Splits up the sulfur -For protein containing
to form Na2S cystine, cysteine or
methionine
- due to the formation of
- black ppt. lead sulfide
Lead acetate
6. Lieberman’ s test Conc. HCl, sucrose Violet color Presence of tryptophan
soln.
7. Molisch’s test H2SO4 Violet ring Presence of glycol-protein
develops
8. Ninhydrin Triketohydrindene Blue color Due to the presence of
reaction hydrate the α-amino group in the
molecule except for
proline and
hydroxyproline
9. Sakaguchi Alkaline solution, a- Red color Presence of arginine
reaction naphthol and sodium
hypochlorite
