Nanosecond photoreduction of inducible nitric oxide synthase by a Ru-diimine electron tunneling wire bound distant from the active site

A Ru-diimine wire, [(4,4′,5,5′-tetramethylbipyridine)_2Ru(F_9bp)]^(2+) (tmRu-F_9bp, where F_9bp is 4-methyl-4′-methylperfluorobiphenylbipyridine), binds tightly to the oxidase domain of inducible nitric oxide synthase (iNOSoxy). The binding of tmRu-F_9bp is independent of tetrahydrobiopterin, arginine, and imidazole, indicating that the wire resides on the surface of the enzyme, distant from the active-site heme. Photoreduction of an imidazole-bound active-site heme iron in the enzyme-wire conjugate (k_(ET) = 2(1) × 10^7 s^(−1)) is fully seven orders of magnitude faster than the in vivo process.