Millon’s test: (Test For Detection of Tyrosine)
Amino Acid Tyrosine (Hydroxyphenylalanine) and other phenolic compounds give this reaction. Millon’s test is used for the detection of amino acid tyrosine.
Millon’s Reagent: Mixture of mercurous and mercuric nitrates.
The mercurous and mercuric nitrate reacts with the hydroxybenzene radicals (Phenols) forming a red coloured compound. In other words, Millon’s reagent reacts with Phenolic group of tyrosine to form mercuric fumarate which gives pinkish or red coloured compound.
PROCEDURE OF Millon’s test:
If you want to find the presence of tyrosine (an amino acid) in a given solution then just follow the below procedure of Millon’s test, and you will find whether the given solution contains tyrosine or not.
- First of all take 2ml of original solution (protein solution) in a test tube.
- Then add a few drops of the Millon’s reagent to the test tube containing the original solution.
- Hold the test tube by using test tube holder and boil the test tube gently for half a minute.
Also check: Heat Coagulation test for protein
You will observe the solution turn red or a red Precipitate is produces. The proteins, on the addition of Millon’s reagent, form a white precipitate first due to denaturation of proteins by mercury salts, which upon heating turn red.
If the solution on heating turns reddish in colour, then tyrosine is present in the solution.
Tyrosine is the only amino acid which gives this reaction.
Precautions of Millon’s test:
Here are some steps which should be followed for a more accurate result before and while performing the experiments.
- The first step is to wash the apparatus before and after the experiment neatly.
- Test tube should be free of impurities and have washed out neatly before pouring chemicals into it.
- Carefully measure the solution before adding it to the test tube.
- Carefully handle the test tube near the fire burner.
- Prevent prolonged heating of the test tube. Otherwise, it will give you the false result.
If you follow all the Steps mentioned above with better precautions, you will get the positive result that is reddish colour if tyrosine is present in the solution.