Purification and primary structure of galanin from the alligator stomach.

Galanin-like immunoreactivity (6 pmol/g tissue) was detected by radioimmunoassay in an extract of the stomach of the alligator, Alligator mississipiensis, but the peptide was present only in low concentration (< 0.5 pmol/g) in extracts of the brain and small intestine. Alligator galanin comprises 29 amino acid residues and contains an alpha-amidated C-terminal residue. Residues 1-22 of alligator galanin are identical to the corresponding sequence in pig/sheep/rat galanins, demonstrating that strong evolutionary pressure has acted to conserve the receptor-binding domain of the peptide. Unexpectedly, in view of the close phylogenetic relationship between crocodilians and birds, alligator galanin is structurally more similar to sheep galanin (three amino acid substitutions) than to chicken galanin (four amino acid substitutions).