Reactivity of canonical bacterial cytochrome c peroxidases: insights into the electronic structure of Compound I

Abstract

Bacterial cytochrome c peroxidase (bCcP) family members include di-heme enzymes that are capable of producing various high oxidation states in their reactions with the substrate H2O2. Canonical family members such as the enzyme from Nitrosomonas europaea (Ne) are responsible for the detoxification of H2O2 in the periplasm of many Gram negative organisms. Elucidation of the electronic structure of the kinetic intermediates for canonical bCcP enzymes has yet to be attained, through the ortholog MauG and others have evoked a Fe(IV) Fe(IV)=O species capable of long-range oxidation. Here, we use a combination of optical, electron paramagnetic and Mössbauer spectroscopies to demonstrate that the first species produced upon the reaction of the diferric form of Ne bCcP is a ferryl peroxidatic heme that is coupled to a porphyrinyl radical, with an unexpected exchange coupling constant J of -17 cm-1 (Hex = JSFe•Spor).