The role of tyrosine residues in the RNA N-glycosidase activity of cinnamomin A-chain.

Cinnamomin is a type II ribosome-inactivating protein (RIP) and its A-chain (CTA) is a RNA N-glycosidase. It is observed that modification of tyrosine residues by N-acetylimidazole (N-AI) causes almost complete loss of CTA activity. Adenine partially protects tyrosine residues from modification by N-AI. It is proposed that tyrosine residues are involved in the active site of CTA and they are crucial in recognition and binding of ribosomal RNA. Tryptophan residues of CTA are also studied by NBS modification.