3. Proteins give a number of colour reactions. Specific
colour obtained with certain reagents are used for
identification of amines. Most of these colour test
depends reaction due to groups contained in one or
more of the constituent amino acids. Thus the
presence are absence of proteins shown by using
several tests.
4. Given substance is dissolved or suspended in a
strong caustic soda solution. A few drop of
dilute copper sulphate solution are added to
the above solution when violet colour is
obtained, a protein is present.
5.
6. Given substance is warmed with nitric acid. A
yellow color , if produced , indicates the
presence of protein.
Yellow stain on fingers while working with
nitric acid is due to this reaction .
the formation of yellow color is due to
nitration of aromatic side chain of amino acids.
7.
8. Millon’s reagent is prepared by dissolving
mercurous and mercuric nitrate in nitric acid.
an adding this solution to a solution of protein
, white precipitate is obtained which turned
brick red colour on boiling.
This test is characteristics of -OH group
present in a protein molecule.
9.
10. An alcoholic solution of 1-naphthol is added to
the protein solution taken in a test tube .
Concentrated sulphuric acid is then poured
slowly along the sides of the test tube.
A violet colour is obtained at the junction of the
two liquids
This test is given only by those proteins which
contain a carbohydrate.
11.
12. Protein solution is mixed with a little glyoxalic
acid and concentrated sulphuric acid is poured
along the sides of the test tube blue-violet
colour is obtained.
13.
14. The given protein solution is boiled with
caustic soda and lead acetate. A black
precipitate is obtained.
This test is characteristics of –S-S- or –SH
groups.
15.
16. Proteins, having free –COOH and –NH2
groups, give an intense blue colour with
ninhydrin.
This is an extremely delicate test.
