The peroxidase-catalyzed oxidation of kyotorphins

In vitro experiments are reported showing that the dipeptides Tyr-L-Arg (kyotorphin) and Tyr-D-Arg (D-Arg-kyotorphin) can be oxidized by H2O2-horseradish peroxidase system: the products formed are characterized by absorption spectra with two peaks at 290 nm and 315 nm. The effects of substrate and enzyme concentration on the oxidation rate are described. Amino acid analysis of hydrolysates of peroxidase-treated kyotorphins provides evidence for the presence of dityrosine. The data suggest that the oxidation leads to the production of dimers with an o,o-linkage between the tyrosine residues.