Characterization of endogenous neuropeptide Y in rat hippocampus and its metabolism by nanospray mass spectrometry

Neuropeptide Y (NPY) is a 36-residue-long neuropeptide which has been implicated in the regulation of feeding behavior and modulation of the circadian rhythm. We identified the primary structure of the endogenous NPY-immunoreactive material in the rat hippocampus using a combination of chromatographic techniques and nanospray mass spectrometry. The major component in the brain tissue corresponded to the authentic amidated form of NPY(1-36). The fate of NPY in the central nervous system was studied by subjecting pure peptide to the protease(s) present in hippocampal synaptosomes to reveal potential cleavage site(s). NPY was efficiently metabolized with a single cleavage between Leu30-Ile31. Thus, processing of NPY resulted in formation of the C-terminally truncated fragment NPY(1-30) and its counterpart NPY(31-36). The enzyme revealed properties of aspartic protease, being blocked by pepstatin and having a pH optimum between 4 and 5. The data clarify the structure of NPY and its inactivation pathway in the brain, which is different from that found in the periphery, and may have important consequences in vivo.