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Primary Structures of Somatostatins from the Islet Organ of the Hagfish Suggest an Anomalous Pathway of Posttranslational Processing of Prosomatostatin-1^*

Clinical Research Group for Gastrointestinal Endocrinology of the Max-Planck-Society, University of Gottingen, Federal Republic of Germany (J.M.C.); Department of Tumor Pathology, Karolinska Institute, Stockholm, Sweden (U.A., S.F.); and Novo Research Institute Bagsvaerd, Denmark (L.T.)

Address requests for reprints and all correspondence to: J. M. Conlon, Klinische Arbeitsgruppe der Max-Planck-Gesellschaft, Gosslerstrasse 10D, D-3400 Gottingen, Federal Republic of Germany.

Abstract

The cyclostomes represent the first class of vertebrate in evolution to develop an endocrine pancreas. Two peptides with somatostatin-like immunoreactivity were isolated from the islet organ of one such cyclostome, the Atlantic hagfish (Myxine glutinosa). The primary structure of the more abundant peptide was established as: Ala-Val-Glu-Arg-Pro⁵-Arg-Gln-Asp-Gly-Gln¹⁰-Val-His-Glu-Pro-Pro¹⁶-Gly-Arg-Glu-Arg-Lys²⁰-Ala-Gly-Cys-Lys-Asn²⁵-Phe-Phe-Trp-Lys-Thr³⁰-Phe-Thr-Ser-Cys.

The second peptide, comprising 27% of the total immunoreactivity in the islet extract, was identical to mammalian somatostatin-14. The pathway of posttranslational processing of prosomatostatin in the hagfish islet differs markedly from the pathway in the higher vertebrates. In the mammalian pancreas, prosomatostatin is cleaved at the site of the single arginyl residue (corresponding to position 6 in hagfish somatostatin-34) and at the arginine-lysine site (corresponding to positions 19 and 20 in the hagfish peptide) to generate somatostatin-14 and somatostatin-28(l–12)-peptide. In the hagfish islet, Arg6 is not used as a cleavage site and cleavage at Arg¹⁹-Lys20 represents only a minor pathway of processing. The data provide further evidence of the strong evolutionary pressure to conserve the complete amino acid sequence of somatostatin-14. (Endocrinology 122: 1855–1859, 1988)

Footnotes

^* This work was supported by the Stiftung Volkswagenwerk, the Swedish Medical Research Council (Project 12X-718), the Swedish Diabetes Association and the Cancer Society of Stockholm.

Received November 3, 1987.

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