O2 Activation by Non-Heme Iron Enzymes

The non-heme Fe enzymes are ubiquitous in nature and perform a wide range of functions involving O-2 activation. These had been difficult to study relative to heme enzymes; however, spectroscopic methods that provide significant insight into the correlation of structure with function have now been developed. This Current Topics article summarizes both the molecular mechanism these enzymes use to control O-2 activation in the presence of cosubstrates and the oxygen intermediates these reactions generate. Three types of O-2 activation are observed. First, non-heme reactivity is shown to be different from heme chemistry where a low-spin Fe-III-OOH non-heme intermediate directly reacts with substrate. Also, two subclasses of non-herne Fe enzymes generate high-spin Fe-IV=O intermediates that provide both sigma and pi frontier molecular orbitals that can control selectivity. Finally, for several subclasses of non-herne Fe enzymes, binding of the substrate to the Fe-II site leads to the one-electron reductive activation of O-2 to an Fe-III-superoxide capable of H atom abstraction and electrophilic attack.