The degradation of the neuropeptide galanin(1-29) and its fully active synthetic N-terminal fragment galanin(1-16) in hypothalamic tissue, where these peptides potently affect feeding behaviour, is studied. Galanin(1-29) had a half-life of 100 min while galanin(1-16) had a half-life of 28 min when incubated with a hypothalamic membrane preparation. The putative sites of peptidolytic cleavage of the active N-terminal fragment galanin(1-16) were determined as being between amino acids Leu4 and Asn5, between Asn5 and Ser6, and between His14 and Ala15, respectively. The synthetic analogs of galanin(1-16) where Leu4, Asn5 or Ser6 was substituted by Ala were all more stable to peptidolysis; [Ala4]galanin(1-16) had a half-life of 55 min. Cleavage of the galanin(1-16) between His14-Ala15 yields a ligand-galanin(1-14) which binds to the receptor with high affinity (KD approximately 10(7) M), while cleavage at amino acid residues Leu4, Asn5 and Ser6 results in inactive peptide fragments with affinities for the galanin receptor below 10(-4) M. The enzyme(s) responsible for degradation of galanin were identified as endopeptidase(s), which were partially inhibited by bacitracin (1 mg/ml) by up to 50%, but not significantly by EDTA (1 mM), phosphoramidon (1 microM), phenylmethylsulfonyl fluoride, (100 microM) or aprotinin (10 micrograms/ml).
Amino Acid Sequence Animals