Characterization of [H]Propionylated Human Peptide YY-A New Probe for Neuropeptide Y Y Receptor Binding Studies.

The neuropeptide Y (NPY) Y receptor (YR) is a G-protein-coupled receptor that is involved in the regulation of various physiological processes such as neurotransmitter release, bone metabolism, and memory. Consequently, the YR represents a potential drug target, e.g., for the treatment of epilepsy and mood disorders. Until now, the determination of the YR binding affinities of YR ligands has primarily been performed using I-labeled derivatives of the endogenous YR agonists NPY and peptide YY (PYY). A tritium-labeled NPY derivative has also been used; however, its suitability for binding assays in sodium-containing buffer is doubtful. We synthesized a tritium-labeled PYY derivative by [H]propionylation at Lys ([H]). The radioligand was characterized by saturation binding, association, and dissociation kinetics and was applied in competition binding assays. Specific binding of [H] at intact Chinese hamster ovary cells expressing the hYR was saturable in both sodium-free buffer (apparent = 0.016-0.067 nM) and sodium-containing buffer (175 mM Na, apparent = 0.16-0.18 nM). Competition binding experiments with YR reference ligands yielded values, which are in good agreement with the reported YR binding affinities, showing that [H] represents a useful tritiated tool compound for the determination of YR binding affinities also in buffers containing sodium at physiological concentrations.