Intermediates in the reaction of substrate-free cytochrome P450 cam with peroxy acetic acid

Abstract

Freeze-quenched intermediates of substrate-free cytochrome 57Fe-P450 cam in reaction with peroxy acetic acid as oxidizing agent have been characterized by EPR and Mössbauer spectroscopy. After 8 ms of reaction time the reaction mixture consists of ∼90% of ferric low-spin iron with g-factors and hyperfine parameters of the starting material; the remaining ∼10% are identified as a free radical ( S′=1/2) by its EPR and as an iron(IV) ( S=1) species by its Mössbauer signature. After 5 min of reaction time the intermediates have disappeared and the Mössbauer and EPR-spectra exhibit 100% of the starting material. We note that the spin-Hamiltonian analysis of the spectra of the 8 ms reactant clearly reveals that the two paramagnetic species, e.g. the ferryl (iron(IV)) species and the radical, are not exchanged coupled. This led to the conclusion that under the conditions used, peroxy acetic acid oxidized a tyrosine residue (probably Tyr-96) into a tyrosine radical (Tyr -96), and the iron(III) center of substrate-free P450 cam to iron(IV).