Xanthoprotein reaction
The xanthoprotein reaction ( Greek : xanthos "yellow", proteuo "first") is a detection reaction for aromatic amino acids in proteins . The aromatic amino acids include those that contain a benzene ring ( phenylalanine , tyrosine, and tryptophan ).
When nitric acid (HNO 3 ) is added, nitration takes place on the benzene ring.
If the nitric acid is added to egg white, flocculation takes place, which is due to the denaturation of the egg white by the acid. If this solution is additionally heated, a yellow nitro compound is formed. One hydrogen atom is substituted by the NO 2 group (from nitric acid). Similarly, the skin turns yellow on contact with concentrated nitric acid, as skin cells also contain proteins with aromatic amino acids.
Further detection reactions for proteins
Individual evidence
- ↑ Beyer-Walter: Textbook of Organic Chemistry , 23rd Edition, S. Hirzel Verlag 1998 ISBN 3-7776-0808-4 .