BIOMOLECULES AND ENZYMES

Detailed explanation-1: -Imino acids, e.g. proline and hydroxyproline, react with ninhydrin to give a yellow color. At higher temperatures (" 100°C), the yellow compound (X) is trans-formed to the purple-red compound (XI) 1°.

Detailed explanation-2: -Proline gives a yellow colour because it is a secondary amine. Most amino acids are primary amines with the general structure H2NCHRCOOH . Except for proline and hydroxyproline, all the -amino acids are oxidized by ninhydrin to give the same intensely colored purple anion.

Detailed explanation-3: -Ninhydrin Test Principle Now, the ammonia goes on to react with another ninhydrin molecule to form diketohydrin (which is also known as Ruhemann’s complex). This complex is responsible for the deep blue colour. When the analyte contains Imino-acids like proline, a yellow coloured complex is formed.

Detailed explanation-4: -Xanthoproteic Test In this reaction, the aromatic rings become nitrated. When nitric acid is added to a sample and the mixture is heated, a yellow solution will result if the sample contains tyrosine or tryptophan.

Detailed explanation-5: -Additionally, proline is the only amino acid that does not form a red-purple colour when developed by spraying with ninhydrin for uses in chromatography. Proline, instead, produces an orange-yellow colour.