Non-heme iron enzymes: Contrasts to heme catalysis

Non-heme iron enzymes catalyze a wide range of O-2 reactions, paralleling those of heme systems. Non-heme iron active sites are, however, much more difficult to study because they do not exhibit the intense spectral features characteristic of the porphyrin ligand. A spectroscopic methodology was developed that provides significant mechanistic insight into the reactivity of non-heme ferrous active sites. These studies reveal a general mechanistic strategy used by these enzymes and differences in substrate and cofactor interactions dependent on their requirement for activation by iron. Contributions to O-2 activation have been elucidated for non-heme relative to heme ligand sets, and major differences in reactivity are defined with respect to the heterolytic and homolytic cleavage of O-O bonds.