The First Stage a-meso-Hydroxylation

The Fe -02 complex can be observed as an intermediate in the catalytic process (Fig. 4), but must be reduced further for heme oxidation to occur (4). A two-electron reduction of molecular oxygen produces a species formally equivalent in oxidation state to H2O2. We therefore examined the possibility that H2O2 might be a viable substitute for molecular oxygen and reducing equivalents in supporting the catalytic 

In one study, it has been reported that radiolytic reduction of the Fe - 

If the a-meso regioselectivity of hydroxylation is not inherent to the heme group, as indicated by the fact that all four isomers are obtained by coupled heme oxidation (40), how is the regiochemistry of heme oxidation influenced by electronic factors One possibility is that the puckering or ruffling of the porphyrin caused by steric clashes between the meso and flanking substituents in the meso-substituted heme probes 

The conversion of a-meso-hydroxyheme to verdoheme is an oxygen-dependent process because the HO-l a-meso-hydroxyheme complex, whether obtained by reconstitution of the apoenzyme with synthetic a-meso-hydroxyheme or from oxidation of the heme complex with H2O2, is stable under anaerobic conditions 104, 105). EPR analysis of the 

The minimal mechanism required for the conversion of a-meso-hydroxyheme to verdoheme requires deprotonation of a-meso-hydroxyheme to produce an Fe radical species that binds oxygen to give an Fe  

---