Biosynthesis of Avian Glucagon: Evidence for a Possible High Molecular Weight Biosynthetic Intermediate

Ak, Tung

doi:10.1055/s-0028-1093915

Cited by 19 publications

(10 citation statements)

References 6 publications

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“…Large mol. wt glucagons which elute with the G-50 void volume have also been reported (Tung, 1973;O'Connor & Lazarus, 1976). We also found that such a compound is secreted from perifused pancreatic pieces (data not shown); however, we were able to demonstrate the phenomenon only as an inconsistent finding in depancreatized chicken plasma.…”

Section: Postmortem Extractionsupporting

confidence: 48%

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Persistence of Immunoreactive Insulin, Glucagon and Pancreatic Polypeptide in the Plasma of Depancreatized Chickens

Colca¹,

Hazelwood²

1982

Journal of Endocrinology

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The present study evaluates the possibility that an extra-pancreatic source of insulin exists in chickens. The effect of pancreatectomy on plasma levels of immunoreactive insulin (IRI), glucagon (IRG) and pancreatic polypeptide (IRAPP) was examined . Plasma levels of IRI, IRG and IRAPP were measured both in the basal state and after an i.v. challenge with known secretogogues at several times after pancreatectomy. The nature of the avian plasma immunoreactivity was further characterized by gel filtration. Results indicated that plasma IRI and IRG persisted for 5 h, 24 h and 5 days after pancreatectomy. Furthermore, plasma levels of IRI and IRG remained responsive to the stimulus of i.v. arginine. The Sephadex G-50 elution profiles for IRI and IRG were similar for plasma obtained from both depancreatized and intact chickens. Postmortem tissue analyses indicated that the persistence of IRI and IRG in the depancreatized animals was not due to the presence of pancreatic remnants. Plasma IRAPP decreased to undetectable levels 5h after pancreatectomy. Although plasma IRAPP was measurable 1 and 5 days after pancreatectomy, these levels were not responsive to i.v. pentagastrin. Furthermore, gel filtration experiments indicated that the only form of IRAPP remaining after pancreatectomy had an apparent mol. wt of greater than 100 000. Such a compound was not secreted by the pancreas in vitro. Evidence presented herein indicates that pancreatic polypeptide is the only pancreatic hormone to be eliminated from the circulation after pancreatectomy in chickens. It is suggested that the depancreatized chicken might be useful as a model of a 'selective pancreatic polypeptide deficiency.

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Section: Postmortem Extractionsupporting

confidence: 48%

“…The large mol. wt component may represent some form of proglucagon (Tung, 1973) and, as such, contribute to the hyperglucagonaemia observed in depancreatized animals (Valverde, Dobbs & Unger, 1975).…”

Section: Postmortem Extractionmentioning

confidence: 99%

Persistence of Immunoreactive Insulin, Glucagon and Pancreatic Polypeptide in the Plasma of Depancreatized Chickens

Colca¹,

Hazelwood²

1982

Journal of Endocrinology

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“…Some biochemical studies of glucagon biosynthesis in islets from the duck (KRUG and MIALHE, 1970;KRUG et al, 1971) and the pigeon (TUNG and ZEREGA, 1971;TUNG, 1973TUNG, , 1974 showed a rapid incorporation of the labeled amino acid into proglucagon with little incorporation into glucagon.…”

Section: Discussionmentioning

confidence: 99%

Fine Structure of the Pancreatic Islets in Domestic Fowl with Special Reference to the Cell Type and Secretion

Watanabe

Paik

Yasuda

1975

Arch. Histol. Jap., Arch. Histol. Jpn

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“…Reports of analyses of newly labeled proteins in mammalian (6, 7), avian (8), and fish (9) islets indicate that pancreatic glucagon is synthesized in the form of a large precursor (8000-18,000 daltons). Structural analyses of glicentin, a 69-amino acid peptide isolated from porcine intestine, revealed the structure of glucagon with both NH2-and COOH-terminal extensions (10).…”

mentioning

confidence: 99%

Pancreatic preproglucagon cDNA contains two glucagon-related coding sequences arranged in tandem.

Lund¹,

Goodman²,

Dee³

et al. 1982

Proc. Natl. Acad. Sci. U.S.A.

224

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We have constructed and cloned in bacteria recombinant plasmids containing DNA complementary to the mRNA encoding a pancreatic preproglucagon (Mr 14,500), a product of cell-free translation of angler fish islet mRNAs shown previously by immunoprecipitation analyses to be a precursor of glucagon. cDNAs of 630, 180, and 120 base pairs were isolated and correspond to most of the mRNA for the preproglucagon (650 bases). The cDNAs contain a protein coding sequence of 372 nucleotides and 5'-and 3'-untranslated regions of 58 and 206 nucleotides, respectively. From the coding sequence of the cDNAs, we find that the sequence of glucagon, identical to mammalian glucagon in 20 of29 positions, resides in the preproglucagon of 124 amino acids flanked by NH2-and COOH-peptide extensions of 52 and 43 amino acids, respectively. The peptide extensions are linked to the glucagon by Lys-Arg sequences characteristic of the sites that are cleaved during the posttranslational processing of prohormones. Notable is the finding that, following the initial Lys-Arg sequence in the COOH-peptide extension is a pentapeptide, Ser-Gly-Val-Ala-Glu, followed by another Lys-Arg and a sequence of 34 residues that shows striking homology with glucagon and the other peptides of the glucagon family-gastric inhibitory peptide, vasoactive intestinal peptide, and secretin. Thus, the preproglucagon mRNA contains two glucagon-related coding sequences arranged in tandem. The finding of Lys-Arg sequences flanking the glucagon and glucagon-related sequences suggests that these two peptides and a pentapeptide are formed in vivo by posttranslational cleavages of a common precursor.Glucagon is a 29-amino acid peptide hormone (Mr 3500) produced in the A cells of the pancreatic islets (1). The hormone belongs to a multigene family of structurally related peptides that include secretin, gastric inhibitory peptide, vasoactive intestinal peptide, and glicentin (2). These peptides variously regulate carbohydrate metabolism, gastrointestinal motility, and secretory processes (1, 3). In addition to their location in the islets and the gastrointestinal tract, substances that have glucagon-like immunoreactivity have been found in the central nervous system where they may be involved in neuroregulation (4). The principal recognized actions of pancreatic glucagon, however, are to promote glycogenolysis and gluconeogenesis, resulting in an elevation of blood sugar levels. In this regard, the actions ofglucagon are counter regulatory to those ofinsulin and may contribute to the hyperglycemia that accompanies diabetes mellitus (5).Interest has focused on studies of the biosynthesis of the glucagon-related peptides because oftheir widespread distribution in different tissues and their importance in the regulation of carbohydrate metabolism and possible functions as neuropeptides. Reports of analyses of newly labeled proteins in mammalian (6, 7), avian (8), and fish (9) islets indicate that pancreatic glucagon is synthesized in the form of a large precursor (8000-18,000...

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Biosynthesis of Avian Glucagon: Evidence for a Possible High Molecular Weight Biosynthetic Intermediate

Cited by 19 publications

References 6 publications

Persistence of Immunoreactive Insulin, Glucagon and Pancreatic Polypeptide in the Plasma of Depancreatized Chickens

Persistence of Immunoreactive Insulin, Glucagon and Pancreatic Polypeptide in the Plasma of Depancreatized Chickens

Fine Structure of the Pancreatic Islets in Domestic Fowl with Special Reference to the Cell Type and Secretion

Pancreatic preproglucagon cDNA contains two glucagon-related coding sequences arranged in tandem.

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