Colour reactions of protein

organic chemistry colour reactions of protien with equation

1. N.Gokila III B.Sc Chemistry S.B.K College

2. Colour reactions of proteins

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 o r absence of proteins shown by using several tests.

4. Biuret test 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. Xanthoprotein test 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.

6. Millon’s test 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.

7. Molisch’s test 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.

8. Hopkins colour test Protein solution is mixed with a little glyoxylic acid and concentrated sulphuric acid is poured along the sides of the test tube blue-violet colour is obtained.

9. Lead sulphide test 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.

10. Ninhydrin test Proteins, having free –COOH and –NH 2 groups, give an intense blue colour with ninhydrin. This is an extremely delicate test.

11. Ninhydrin Amino acid

12. Coagulation test The protein solution is acidified with acetic acid and heated. Coagulation indicates the presence of albumin, a simple protein.

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