BIOMOLECULES AND ENZYMES

Detailed explanation-1: -Xanthoproteic test is used to detect amino acids containing an aromatic nucleus (tyrosine, tryptophan and phenylalanine) in a protein solution which gives yellow color nitro derivatives on heating with conc. HNO3. The aromatic benzene ring undergoes nitration to give yellow colored product.

Detailed explanation-2: -The xanthoproteic reaction is a method that can be used to detect a presence of protein soluble in a solution, using concentrated nitric acid. The test gives a positive result in amino acids carrying aromatic groups, especially in the presence of tyrosine.

Detailed explanation-3: -Millon’s test is specific to phenol containing structures (tyrosine is the only common phenolic amino acid). Millon’s reagent is concentrated HNO3, in which mercury is dissolved. As a result of the reaction a red precipitate or a red solution is considered as positive test.

Detailed explanation-4: -All aryl amino acids give xanthoproteic test except phenylalanine, this is so because the benzene group present in phenylalanine is very stable and it does not react with nitric acid in normal conditions. Therefore, all amino acids do not give a positive xanthoproteic test.

Detailed explanation-5: -The xanthoproteic test is specific for aromatic compounds such as tyrosine, tryptophan and phenyalanine. Xanthoproteic acids are also formed when the acid contacts epithelial cells (typically the fingers) and are a certain giveaway of inadequate care when handling nitric acid.