Model Studies for Heme Oxygenase-Catalyzed Porphyrin Meso Hydroxylation

Nonenzymatic model studies based on a porphyrin analogue (2,4-diacetyldeuteroporphyrin) that avoid the steric effect complications of the heme oxygenase active site were carried out to determine the polarity of the ferric hydroperoxide attacking species. Mass spectral and deuterium-labeling experiments indicate that the porphyrin meso positions that are at higher π-electron densities in ferric 2,4-diacetyldeuteroporphyrin are selectively attacked. This supports an electrophilic aromatic substitution mechanism for the heme oxygenase-catalyzed porphyrin meso hydroxylation.