title: Primary structure of insulin and a truncated C-peptide from an elasmobranchian fish, Torpedo marmorata.
abstract: Insulin has been isolated from the pancreas of Torpedo marmorata, an elasmobranchian fish, and shown to contain 21 amino acid residues in the A-chain and 30 residues in the B-chain. The sequence of insulin has been strongly conserved within the class Elasmobranchii with only one substitution and one deletion in the A chain and one substitution in the B-chain compared with insulin from the spiny dogfish, Squalus acanthias. A second peptide, present in the pancreatic extracts in approximately equimolar concentration with insulin, was identified as a heptadecapeptide. The sequence of this peptide shows homology to the N-terminal region of anglerfish (Lophius americanus) C-peptide at six of 17 sites. The isolation of a truncated C-peptide suggests either that the sequence encoding the COOH-terminal region of T. marmorata C-peptide has been deleted from the preproinsulin gene or that a larger C-peptide has undergone a proteolytic cleavage in the central portion of the molecule during packaging in the secretory granules of the B cell.
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002096:C-Peptide / Q000302:isolation & purification*; D002851:Chromatography, High Pressure Liquid; D004284:Dogfish; D005399:Fishes; D006801:Humans; D007328:Insulin / Q000302:isolation & purification*; D010179:Pancreas / Q000032:analysis*; D011863:Radioimmunoassay; D014101:Torpedo / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D002096:C-Peptide; D007328:Insulin