Probing the Active Site of Amine Oxidase with Electron Tunneling Wires

Abstract

Amine oxidases (AO) are copper-containing enzymes that catalyze the conversion of amines to aldehydes. The active site is deeply buried within the protein network, a factor which has precluded many investigations into the mechanism. A series of electron tunneling molecular wires has been synthesized, designed to access the cofactors of amine oxidase by means of the substrate channel. These wires are comprised of phenyl-ethynyl units and thus promote rapid rates of electron transfer to the active site. An amine group attached to one end of the oligomer serves as the channel-specific functionality, which binds within the channel. Binding of the oligomers to AO was demonstrated through inhibition and fluorescence quenching studies. A variety of reporter groups has been attached to the chain end opposite the amine group, allowing us to probe the enzyme using a variety of techniques. A Re terminated complex was designed for electron transfer studies with the enzyme. The photophysics of this complex were investigated in the presence of AO. A thiol terminated wire also has been synthesized, which was employed in electrochemical studies of the amine oxidase cofactors. These studies provide evidence for the ability to communicate with the active site using the molecular wires. In addition, these complexes fulfilled our primary goal and enabled us to determine a redox potential of the TPQ cofactor.