Conjugates of Heme-Thiolate Enzymes with Photoactive Metal-Diimine Wires

Abstract

Heme-thiolate enzymes, notably cytochromes P450 and nitric oxide synthases, use dioxygen to oxygenatesubstrates. Photoactive metal-diimine molecular wires that are capable of effecting rapid redox state changesat 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 induciblenitric oxide synthase (iNOS) primarily by hydrophobic interactions. The wire-binding specificity of eachenzyme is critically dependent on the structural flexibility of the protein. P450CAM:wire conjugates canadopt open or partially open conformations, thereby accommodating a wide range of wires, whereas onlylong wires with smaller [Re(CO)_3(bpy)Im]^+ head groupsare able to bind tightly in the rigid active-site channel of iNOS. Dansyl-terminated molecular wires functionas highly sensitive and isoform specific fluorescent sensors for P450CAM.