Spectroscopic evidence in support of horseradish peroxidase compound II-catalyzed oxidation of salicylic acid but not of phenylethylamine

Salicylic acid and phenylethylamine are putative substrates for naturally occurring reactions for generation of reactive oxygen species, which are catalyzed by plant peroxidases. Here, we used commercially available highly purified horseradish peroxidase-C (HRP-C) as a model enzyme for spectroscopic analysis, and obtained data suggesting that the Compound II form of HRP-C does not utilize phenylethylamine as substrate. In contrast, addition of salicylic acid to Compound II resulted in rapid conversion of Compound II to the native form.