Second‐coordination sphere effects on selectivity and specificity of heme and nonheme iron enzymes

Mononuclear iron containing enzymes are highly versatile oxidants that often react stereospecifically and/or regioselectively with substrates. Combined experimental and computational studies on heme monoxygenases, nonheme iron dioxygenases and halogenases have revealed the intricate details of the second‐coordination sphere that determine this specificity and selectivity. These second‐coordination sphere effects originate from the positioning of the substrate and oxidant, which involve the binding of the co‐factors and substrate into the active site of the protein. In addition, some enzymes affect the selectivity and reactivity through charge‐stabilization from nearby bound cations/anions, an induced electric field or through the positioning of salt‐bridges and hydrogen bonding interactions to first‐coordination sphere iron ligands and/or the substrate. Examples of all of these second‐coordination sphere effects in iron‐containing enzymes and how these influence structure and reactivity are given