Neuropeptide Y (NPY) is a 36-residue peptide isolated from porcine brain. Its complete amino acid sequence was determined using high-performance liquid chromatography (HPLC) for fragment separation and an improved dansyl Edman subtractive technique for sequence analysis. The sequence is: Tyr-Pro-Ser-Lys-Pro-Asp-Asn-Pro-Gly-Glu-Asp-Ala-Pro-Ala-Glu-Asp-Leu-Ala-Arg-Tyr-Tyr-Ser-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu-Ile-Thr-Arg-Gln-Arg-Tyr-NH₂. NPY shows high sequence homology with peptide YY (70%) and pancreatic polypeptide (50%), suggesting they belong to a new peptide family. The discovery of peptide amides in tissue extracts led to the identification of new biologically active peptides, including peptide HI and PYY. These peptides share structural similarities with known hormones and exhibit various biological activities. PYY is structurally similar to pancreatic polypeptide (PP) and inhibits secretin-stimulated pancreatic secretion and gut motility. NPY is abundant in the brain and shares structural similarities with PYY and PP, and also inhibits secretin-stimulated pancreatic secretion. The study re-examined strategies for structural analysis of biologically active peptides. A method combining HPLC for fragment separation and an improved dansyl Edman technique for microsequence analysis was developed. This method allows for the determination of amino acid sequences with high accuracy and efficiency. The technique involves the subtraction of amino acids identified in successive Edman degradation cycles to confirm results and monitor the reaction process. The amino acid composition of NPY was determined to consist of 36 residues, with a high content of tyrosine. Terminal analysis confirmed that NPY has the same NH₂-terminal and COOH-terminal as PYY and the same COOH-terminal as PP. HPLC analysis of tryptic and chymotryptic fragments confirmed the sequence of NPY, showing high homology with PYY and PP. The structural similarities between NPY, PYY, and PP suggest they may be part of a new peptide family. NPY and PYY have distinct sequence homologies to porcine, bovine, and avian PP, with significant homology in the COOH-terminal region. NPY is abundant in the brain and shares structural homologies with bovine and avian PP, suggesting that anti-PP antibodies may cross-react with NPY. NPY and PYY have sequence homologies to members of other peptide families, but their structural similarities to PP are also evident in the identical number of residues and their unique COOH-terminal tyrosine amide structures. They also exhibit similar biological activities, suggesting they may be part of a previously unrecognized peptide family. NPY has potent vasoconstrictorNeuropeptide Y (NPY) is a 36-residue peptide isolated from porcine brain. Its complete amino acid sequence was determined using high-performance liquid chromatography (HPLC) for fragment separation and an improved dansyl Edman subtractive technique for sequence analysis. The sequence is: Tyr-Pro-Ser-Lys-Pro-Asp-Asn-Pro-Gly-Glu-Asp-Ala-Pro-Ala-Glu-Asp-Leu-Ala-Arg-Tyr-Tyr-Ser-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu-Ile-Thr-Arg-Gln-Arg-Tyr-NH₂. NPY shows high sequence homology with peptide YY (70%) and pancreatic polypeptide (50%), suggesting they belong to a new peptide family. The discovery of peptide amides in tissue extracts led to the identification of new biologically active peptides, including peptide HI and PYY. These peptides share structural similarities with known hormones and exhibit various biological activities. PYY is structurally similar to pancreatic polypeptide (PP) and inhibits secretin-stimulated pancreatic secretion and gut motility. NPY is abundant in the brain and shares structural similarities with PYY and PP, and also inhibits secretin-stimulated pancreatic secretion. The study re-examined strategies for structural analysis of biologically active peptides. A method combining HPLC for fragment separation and an improved dansyl Edman technique for microsequence analysis was developed. This method allows for the determination of amino acid sequences with high accuracy and efficiency. The technique involves the subtraction of amino acids identified in successive Edman degradation cycles to confirm results and monitor the reaction process. The amino acid composition of NPY was determined to consist of 36 residues, with a high content of tyrosine. Terminal analysis confirmed that NPY has the same NH₂-terminal and COOH-terminal as PYY and the same COOH-terminal as PP. HPLC analysis of tryptic and chymotryptic fragments confirmed the sequence of NPY, showing high homology with PYY and PP. The structural similarities between NPY, PYY, and PP suggest they may be part of a new peptide family. NPY and PYY have distinct sequence homologies to porcine, bovine, and avian PP, with significant homology in the COOH-terminal region. NPY is abundant in the brain and shares structural homologies with bovine and avian PP, suggesting that anti-PP antibodies may cross-react with NPY. NPY and PYY have sequence homologies to members of other peptide families, but their structural similarities to PP are also evident in the identical number of residues and their unique COOH-terminal tyrosine amide structures. They also exhibit similar biological activities, suggesting they may be part of a previously unrecognized peptide family. NPY has potent vasoconstrictor