1H NMR Relaxation Investigation of Inhibitors Interacting with Torpedo californica Acetylcholinesterase

Two naphthyridines interacting with Torpedo californica acetylcholinesterase (AChE) were investigated. H-1 NMR spectra were recorded and nonselective, selective, and double-selective spin-lattice relaxation rates were measured. The enhancement of selective relaxation rates could be titrated by different ligand concentrations at constant AChE (yielding 0.22 and 1.53 mM for the dissociation constants) and was providing evidence of a diverse mode of interaction. The double-selective relaxation rates were used to evaluate the motional correlation times of bound ligands at 34.9 and 36.5 us at 300 K, Selective relaxation rates of bound inhibitors could be interpreted also in terms of dipole-dipole interactions with protons in the enzyme active site