Purification and structural characterization of insulin from the lesser siren, Siren intermedia (Amphibia: Caudata)

Insulin has been isolated from an extract of the pancreas of a salamander, the lesser siren Siren intermedia, and its primary structure was established as: A-chain, Gly-Ile-Val-Glu-Gln-Cys-Cys-His-Asn-Thr¹⁰-Cys- Ser-Leu-Tyr-Gln-Leu-Glu-Asn-Tyr-Cys²⁰-Asn, and B-chain, Val-Pro-Asn-Lys- Pro-Leu-Cys-Gly-Ala-His¹⁰-Leu-Val-Glu-Val-Met-Tyr-Phe-Val-Cys-Gly²⁰-Asp- Arg-Gly-Phe-Phe-Tyr-Pro-Ser-Ser-Thr^-30. Although those amino acid residues considered to constitute the receptor-binding region of insulin have been retained, siren insulin contains several substitutions (Gln → Lys at B4, Ser → Ala at B9, Ala → Val at B14, Leu → Met at B15, Leu → Phe at B17, Pro → Ser at B28, and Lys → Ser at B29) of amino acid residues that are conserved in insulins from species of other amphibian orders. The biological activity of siren insulin was not investigated in this study but the substitutions at B28 (involved in dimer formation) and at B14 and B17 (involved in hexamer formation) may be expected to influence conformation and therefore biological potency. The data are consistent with the view that the Sirenoidea represent an early divergence from the ancestral stock of salamanders.