Moessbauer and EPR study of reaction intermediates of cytochrome P450

We present a complementary Mossbauer and EPR study on reaction intermediates of substrate-free and substrate-bound cytochrome P450(cam) from Pseudomonas putida prepared by the freeze-quench method from Fe-57-labeled P450(cam) using peroxy acetic acid as oxidizing agent. When reacting the substrate-free P450(cam) for 8 ms reaction time the reaction mixture consists of similar to85% of ferric low-spin iron (Fe(III)) with g-factors and hyperfine parameters of the starting material; the remaining similar to15% are identified as ferryl iron (Fe(IV); S-Fe = 1) by its Mossbauer signature. Parallel to the ferryl iron a tyrosine radical (S-rad = 1 2) is formed. The two paramagnetic species are not exchange-coupled; however, they are close enough to significantly influence the (EPR) relaxation behavior of the radical spin. In the case of substrate-bound P450(cam) only trace amounts of the tyrosine radical are formed within 8 ms (