Commercially available preparations of porcine glucose-dependent insulinotropic polypeptide (GIP) contain a biologically inactive GIP-fragment and cholecystokinin-33/-39.
Commercially available preparations of natural porcine glucose-dependent insulinotropic polypeptide (GIP) were subjected to reverse phase HPLC. The material was found to give rise to 4 peaks which were characterized by HPLC-retention time and N-terminal sequence analysis. They represented: intact porcine GIP(1-42), 58% (wt/wt); the GIP-fragment des-tyr-ala-GIP(3-42), 32% (wt/wt); cholecystokinin (CCK)-33 2% (wt/wt); CCK-39 2% (wt/wt). HPLC-pure GIP(1-42) stimulated insulin release in rat isolated pre-cultured pancreatic islets in the presence of 16.7 mM glucose up to 240% vs. control, whereas the fragment des-tyr-ala-GIP(3-42) did neither increase insulin release nor exhibit antagonistic activity to GIP(1-42) at 100 ng/ml. These results indicate that commercially available porcine GIP-preparations may contain the biologically inactive des-tyr-ala-GIP(3-42) in high amounts, and in addition may be contaminated by CCK-peptides. HPLC-characterization of these peptide preparations prior to any biological study is crucial.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002478:Cells, Cultured; D002766:Cholecystokinin / Q000032:analysis / Q000031:analogs & derivatives; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D005749:Gastric Inhibitory Polypeptide / Q000302:isolation & purification* / Q000494:pharmacology / Q000592:standards; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism; D010446:Peptide Fragments / Q000032:analysis; D051381:Rats; D013552:Swine
D000596:Amino Acids; D007328:Insulin; D010446:Peptide Fragments; D005749:Gastric Inhibitory Polypeptide; C032740:cholecystokinin 39; D002766:Cholecystokinin