Studies were carried out in conscious dogs in which the immunoreactive gastric inhibitory polypeptide (IR-GIP) response to graded doses of oral fat (triglycerides) and glucose was investigated. The IR-GIP response to the doses of triglycerides used was greater and more prolonged than the response to the glucose loads employed. In addition, the relative insulinotropic potencies of exogenous porcine GIP and IR-GIP released by fat as against those released by oral glucose were assessed. When glucose was administered by the oral route, the immunoreactive insulin (IRI) response was magnified above the IRI response to a comparable intravenous glucose load. The serum IRI response to oral glucose was accompanied by a concomitant rise in serum IR-GIP levels, suggesting a causal relationship. IR-GIP released by oral fat was shown to augment the IRI response to an intravenous glucose load, resulting in an improvement of glucose tolerance. Fat-released IR-GIP augmented IRI levels to a lessor degree than either oral glucose or an infusion of porcine GIP.
The effect of highly purified gastric inhibitory polypeptide (GIP) on immunoreactive insulin (IRI) secretion in the conscious fasted dog was investigated. Significant increases in IRI release were observed with intravenous administration of three different doses of GIP. These were accompanied by depression in fasting serum-glucose levels. Preliminary studies were undertaken to determine whether this insulinotropic action of GIP could be attributed to a particular segment of the GIP molecule. GIP fragments produced by cleavage with cyanogen bromide and trypsin showed no significant stimulation of IRI release. The possibility that GIP might itself enhance glucose uptake or potentiate insulin-induced glucose uptake was studied with the rat hemidiaphragm preparation. No such effect was observed. In the light of this and other recent work, it is concluded that GIP is a strong candidate for an active principle in the enteroinsular axis.
1974) Correction to the Amino Acid Sequence of Porcine Motilin. Can. b. Bischem. 52,7-8 A comparison of the electrophoretic mobilities of the tryptic peptides of natural porcine motilin and a synthetic analogue with norleucine substituted for methisnine revealed the absence of the acidic peptide TR3 of the natural material. Kinetic studies with leucine aminopeptidase and dansyl-Edman degradations on this peptide revealed the presence of glutamine at position 14 and not glutamic acid as previously reported. It is suggested that in the earHier preparation of natural porcine rnotilin deamidation of glutamine occurred. Schubert, PI. & Brown, J. C. (1974) Correction to the Amino Acid Sequence of Porcine Motilin. Can. b. Biochem. 52,7-8La cornparaison des mobilites Clectrophorttiques des peptides trypsiques de la motiline porcine naturelle avec celle d'un analoque synthetique dont la mtthionine est remplacee par la norleucine, rtvkle I'absence du peptide acide TR3 du materiel naturel. L'Ctude cinktique des degradations de ce peptide avec la leucine aminopeptase et le dansyl-Edman rbv$le la presence de la glutamine sur le carbone 14 et non de l'acide glutamique comme on l'a rapport6 prtcedemment. I1 est suggQC que dans la prbparation antkrieure de la motiline porcine naturelle, il y a eu dksamidation de la glutamine.[Traduit par le journal]The synthesis of a norleucine analogue of porcine mstilin, a linear sligopeptide with 22 amino acid residues, has been described (1). The analogue in which norleucine was substituted for the methisnine in position 13 has been shown to have greater than 90% of the biological activity of natural motilin. The amino acid sequence of natural porcine motilin has been reported earlier (2). The availability of the synthetic fragment 9-22 and the 1-22 norleucine analogue allowed a comparison of the electrophoretic mobilities of the tryptic peptides of the synthetic and natural polypeptides to be undertaken (Table I ).Tryptic digestion of both synthetic and natural mstilins, 200 pg of each, were performed as previously described (2). High-voltage electrophoresis of the digestion products at pH 6.5 (3 ) revealed the absence of the acidic peptide TR3 in the natural porcine motilin digest. This peptide had earlier been reported to have the amino acid sequence Me t-Glu-Glu-Lys .A further tryptic digest of 1.0 mg of natural porcine motilin was performed to allow isolation of peptides for further analyses. Peptide TR3 was isolated from the digestion mixture by high-voltage electrophoresis at pH 1.9 (2). N-terminal determination (4) revealed that the peptide was pure. High-voltage electrophoresis at pH 6.5 revealed that the peptide was neutral suggesting that one of the two glutamic acid residues possessed an amide group.The position of the glutamine residue was determined employing a kinetic study with leucine aminopeptidase (LAP, Worthington ) (5). One hundred nanomoles of the peptide TR3 were dissolved in 100 pl buffer at pH 8.5 (0.0025 M MgC12 in 0.05 Ad ]Ma-barbitone). To this was added 5.0 pl LA...
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