Conjugates of heme-thiolate enzymes with photoactive metal-diimine wires

Heme-thiolate enzymes, notably cytochromes P450 and nitric oxide synthases, use dioxygen to oxygenate substrates. Photoactive metal-diimine molecular wires that are capable of effecting rapid redox state changes at buried active sites have been developed to generate intermediates in the catalytic cycles of these enzymes. Wires that feature a photoactive head group tethered to an active-site ligand bind P450CAM and inducible nitric oxide synthase (iNOS) primarily by hydrophobic interactions. The wirebinding specificity of each enzyme is critically dependent on the structural flexibility of the protein. P450CAM:wire conjugates can adopt open or partially open conformations, thereby accommodating a wide range of wires, whereas only long wires with smaller [Re(CO) ₃(bpy)Im]⁺ head groups are able to bind tightly in the rigid active-site channel of iNOS. Dansyl-terminated molecular wires function as highly sensitive and isoform specific fluorescent sensors for P450CAM.