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Research Article Free access | 10.1172/JCI109786
Washington University School of Medicine, Department of Medicine-Metabolism Division, St. Louis, Missouri 63110
Department of Medicine, Children's Hospital Medical Center, Boston, Massachusetts 02115
Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02115
Find articles by Oyama, H. in: JCI | PubMed | Google Scholar
Washington University School of Medicine, Department of Medicine-Metabolism Division, St. Louis, Missouri 63110
Department of Medicine, Children's Hospital Medical Center, Boston, Massachusetts 02115
Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02115
Find articles by Hirsch, H. in: JCI | PubMed | Google Scholar
Washington University School of Medicine, Department of Medicine-Metabolism Division, St. Louis, Missouri 63110
Department of Medicine, Children's Hospital Medical Center, Boston, Massachusetts 02115
Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02115
Find articles by Gabbay, K. in: JCI | PubMed | Google Scholar
Washington University School of Medicine, Department of Medicine-Metabolism Division, St. Louis, Missouri 63110
Department of Medicine, Children's Hospital Medical Center, Boston, Massachusetts 02115
Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02115
Find articles by Permutt, A. in: JCI | PubMed | Google Scholar
Published May 1, 1980 - More info
Using a radioimmunoassay with labeled synthetic tetradecapeptide somatostatin, a large amount of immunoreactive somatostatin was found in the principal pancreatic islet of the channel catfish (Ictalurus punctata). The purpose of these experiments was to isolate and characterize the somatostatin-like material. Extracts of islets were chromatographed on a Bio-Gel P-30 column, and over 90% of the immunoreactive somatostatin migrated with proteins at least twice the size of synthetic tetradecapeptide somatostatin. This fraction was further purified by ion-exchange chromatography on carboxymethyl-cellulose and DEAE-cellulose columns. Two peptides were obtained with identical immunoreactivity, which was ∼25% that of the synthetic somatostatin. Each peptide was judged to be >95% pure by thin-layer electrophoresis, polyacrylamide gel electrophoresis at pH 8.9, and highpressure liquid chromatography. Further criteria of purity included amino-terminal analysis of fraction IV yielding only aspartic acid. A total of 1.3 mg of fraction II, and 3.8 mg of fraction IV somatostatin-like peptides were obtained from 10 g of fresh frozen islets.
Characterization of the two peptides revealed both peptides slightly more acidic than synthetic tetradecapeptide somatostatin. Fraction II had an isoelectric point of 8.0-8.3, and fraction IV 8.3-9.0. Molecular weight estimation by sodium dodecyl sulfate-urea polyacrylamide gel electrophoresis revealed similar mobility of both peptides, between pancreatic polypeptide (mol wt 4,500) and glucagon (mol wt 3,500). The mobility was not altered by reduction, and was approximately twice the size of synthetic tetradecapeptide somatostatin (mol wt 1,800). This confirmed that the peptides were single polypeptide chains and not aggregates, or somatostatin bound to larger proteins. Molecular weight determination by gel filtration chromatography on Bio-Gel P-6 in 8 M urea gave an estimated mol wt of 3,700. Amino acid analysis of the two immunoreactive somatostatins indicated that they were very similar in composition. Both pancreatic somatostatins (1 μM) had full biological activity relative to synthetic somatostatin measured as inhibition of growth hormone release from rat anterior pituitary cells.
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