Electron-nuclear double resonance of the hydrogen peroxide compound of cytochrome c peroxidase: identification of the free radical site with a methionyl cluster.

Abstract

The results of electron-nuclear double resonance and EPR studies on the hydrogen peroxide compound of baker''s yeast cytochrome c peroxidase are inconsistent with previous proposals for the source of the EPR signal in this compound, in particular with its identification with an aromatic amino acid radical such as would arise by oxidation of a tryptophanyl side chain. The EPR signal may be associated with a cluster containing at least 1 methionine and in which proximate side chains share the charge created by loss of 1 electron.