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 H₂O₂, 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 H₂O₂ 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, H₂O₂-free conditions).