The synthesis, physical characterization and receptor binding affinity of neuropeptide Y (NPY)

Porcine neuropeptide Y (pNPY) was synthesized by solid-phase techniques and purified by gel filtration and reverse-phase high performance liquid chromatography. It was found to be equipotent to commercial pNPY (Peninsula) in a receptor binding assay (IC50 = 5 nM). Circular dichroic (CD) spectra of the peptide indicates a concentration-independent alpha-helical conformation in aqueous solution ([theta]222 = -13,998, 2.9 X 10(-5) M in 0.1 M sodium phosphate, pH = 8.0). Lowering the pH of the solution to 6.0 produced little change in the CD spectrum, but CD spectra at pH = 4.2 and 1.8 indicated a loss of alpha-helical content of the peptide with decreasing pH. Sedimentation equilibria of synthetic pNPY showed that it is neither wholly monomeric nor dimeric at pH = 4.2 and 8.0. These data suggest an intramolecularly stabilized helical structure similar to the crystal structure of the homologous avian pancreatic polypeptide (APP).