Heme-(hydro)peroxide mediated O- and N-dealkylation - A study with microperoxidase

The mechanism of microperoxidase-8 (MP-8) mediated O- and N-dealkylation wa s investigated. In the absence of ascorbate (peroxidase mode), many unident ified polymeric products are formed and the extent of substrate degradation correlates (r = 0.94) with the calculated substrate ionization potential, reflecting the formation of radical intermediates. In the presence of ascorbate (P450 mode) formation of polymeric products is largely prevented but, surprisingly, dealkylation is not affected. In addi tion, aromatic hydroxylation and oxidative dehalogenation is observed. The results exclude a radical mechanism and indicate the involvement of a (hydr o)peroxo-iron heme intermediate in P450-type of heteroatom dealkylation.