Microperoxidase 8 catalyzed nitration of phenol by nitrogen dioxide radicals

Microperoxidase 8 (MP8) is a heme octapeptide obtained by hydrolytic digest ion of horse heart cytochrome c. At pH below 9, the heme iron is axially co ordinated to the imidazole side chain of His18 and to a water molecule. Rep lacement of this weak ligand by H2O2 allows the formation of high-valent ir on-ore species which are responsible for both peroxidase-like and cytochrom e P450-like activities of MP8. This paper shows that MP8 is able to catalyze the nitration of phenol by ni trite. The reaction requires H2O2 and is inhibited by ligands having a high affinity for the iron, catalase and radical scavengers. This suggests that the nitrating species could be NO2. radicals formed by the oxidation of ni trite by high-valent iron-ore species. This new activity of MP8 opens a new access to nitroaromatic compounds unde r mild conditions and validates the use of this minienzyme to mimick heme p eroxidases, especially in the reactions of NO-derived species with biomolec ules under oxidative stress conditions.