27 Chapter 2 An Interest in Thiolate Coordination and Hydrogen Bonding

Abstract

Biochem. 2009; 103: 906–911. 28 The Gray group has been studying electron transfer in protein systems for the past three decades. During this time a vast amount of information has been collected concerning the nature of the protein matrix and its ability to facilitate such charge transfer reactions. This led to the development of techniques for the covalent attachment of photosensitizers to metalloproteins, and later to the development of compounds consisting of sensitizers linked to substrates (dubbed “wires”) in order to promote interactions between the photosensitizer and the metal active site buried deep within the protein. A Ru-diimine wire, [(4,4’,5,5’-tetramethylbipyridine)2Ru(F9bp)] 2+ (tmRu-F9bp, where F9bp is 4-methyl-4’-methylperfluorobiphenylbipyridine), binds tightly to the oxidase domain of inducible nitric oxide synthase (iNOSoxy). The binding of tmRu-F9bp 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 (kET = 2(1) × 10