Functional important radical-containing intermediates in thiolate-coordinated heme proteins: cytochrome P450 and chloroperoxidase

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It is believed that a compound I type intermediate is involved in the reaction cycle of cytochrome P450; however, its eletronic structure has not been determined until now. Also, it has not been shown that in the shunt pathway, using peroxy acids as oxidizing agents, a Fe(IV)=0 porphyrin p-cation radical system does really exist. We therefore propose to investigate the valence and spin state of iron, the formation of radicals and the possible interaction between iron and radical in P450 reactions by EPR and Mössbauer spectroscopy. For this purpose P450 will be prepared with 57Fe-enriched porphyrin by heme replacement; reaction intermediates using peroxy acids, in the presence and in the absence of substrate, will be trapped by the freeze-quench technique. The studies on P450 will be complemented by a comparative study on 57Fe-enriched chloroperoxidase as another member of the heme-thiolate protein family.