Neuropeptide Y (human) free acid belongs to the pancreatic polypeptide family, plays an important role in circadian rhythms, neurogenesis, and neuroprotection, nociception, feeding behavior, energy regulation, neuronal excitability, emotion, cognition, and stress response. The amidation of Neuropeptide Y C-terminal tyrosine is critical for its function. Non-amidated Neuropeptide Y fails to elicit G protein signaling.