Horseradish‐Peroxidase‐Catalyzed Tyrosine Click Reaction

The efficiency of protein chemical modification on tyrosine residues with N ‐methylluminol derivatives was drastically improved by using horseradish peroxidase (HRP). In the previous method, based on the use of hemin and H 2 O 2 , oxidative side reactions such as cysteine oxidation were problematic for functionalization of proteins selectively on tyrosine residues. Oxidative activation of N ‐methylluminol derivatives with a minimum amount of H 2 O 2 prevented the occurrence of oxidative side reactions under HRP‐catalyzed conditions. As probes for HRP‐catalyzed protein modification, N ‐methylluminol derivatives showed much higher efficiency than tyramide without inducing oligomerization of probe molecules. Tyrosine modification also proceeded in the presence of β‐nicotinamide adenine dinucleotide (NADH, H 2 O 2 ‐free conditions).