Xanthoproteic reaction

The Xanthoproteic reaction (Greek: xanthos "yellow", proteuo " I'll take the first place ") is a detection reaction for aromatic amino acids in proteins. To the aromatic amino acids include those which contain a benzene ring ( phenylalanine, tyrosine and tryptophan).

With the addition of nitric acid (HNO3), nitration on the benzene ring takes place.

The nitric acid are added to the egg white, the flocculation takes place which is due to the denaturation of the albumen of the acid. When heated in addition, this solution gives a yellow nitro compound. In this case, a hydrogen atom by the NO2 group ( from nitric acid ) is substituted. Thus, the skin changes color upon contact with concentrated nitric acid yellowish because skin cells contain proteins with aromatic amino acids.

Further detection reactions for proteins

• Biuret
• Millon reaction
• Ninhydrin reaction
• Bradford assay
• Protein determination according to Lowry