Below are test used to test for amino acid and proteins:
1) Ninhydrin reaction – test for amnio acids
The reagent ‘Ninhydrin’ (triketohydrindene hydrate) is of great value in the detection and quantitative estimation of amino acids in chromatographic procedures.
Amino acid + ninhydrin → aldehyde + CO2 + NH3 + reduced ninhydrin
Reduced ninhydrin + NH3 + ninhydrin → purple compound
The amino acids proline and hydroxyproline give a yellow colour.
Biuret test test for protein
When urea is heated, it decomposes to give the compound ‘biuret’.
2H2NCO-NH2 → H2NCONHCONH2 + NH3
This compound reacts with cupric ions in alkaline solution to give a deep purple colour. Compounds containing two or more peptide bonds also give the reaction. The reaction with proteins is thus specific for the peptide bond. The Biruet test may be used for quantitative estimation of proteins but requires relatively large amounts of protein (1 – 20mg).
BIOCHEM 