The copper amine oxidase from Arthrobacter globiformis (AGAO) is reversibly inhibited by molecular wires comprising a Ru(II) complex head group and an aromatic tail group joined by an alkane linker. The crystal structures of a series of Ru(II)-wire-AGAO complexes differing with respect to the length of the alkane linker have been determined. All wires lie in the AGAO active-site channel, with their aromatic tail group in contact with the trihydroxyphenylalanine quinone (TPQ) cofactor of the enzyme. The TPQ cofactor is consistently in its active ("off -Cu") conformation, and the side chain of the so-called "gate" residue Tyr296 is consistently in the "gate-open" conformation. Among the wires tested, the most stable complex is produced when the wire has a -(CH2)(4)- linker. In this complex, the Ru(II)(phen)(bpy)(2) head group is level with the protein molecular surface. Crystal structures of AGAO in complex with optically pure forms of the C-4 wire show that the linker and head group in the two enantiomers occupy slightly different positions in the active-site channel. Both the A and A isomers are effective competitive inhibitors of amine oxidation. Remarkably, inhibition by the C-4 wire shows a high degree of selectivity for AGAO in comparison with other copper-containing amine oxidases.