title: Dual calcium-dependent protein phosphorylation systems in pancreas and their differential regulation by polymyxin B1.
abstract: Both phospholipid/calcium (PL/Ca2+) activated and calmodulin/Ca2+ (CaM/Ca2+)activated protein kinase systems were found in rat pancreatic extracts treated with Sephadex G-25. At least four substrate proteins for PL/Ca2+-activated kinase and one for a CaM/Ca2+-activated kinase were noted. Polymyxin B, an amphipathic antibiotic, was over 100-fold more potent as an inhibitor of PL/Ca2+-dependent protein phosphorylation than of the CaM/Ca2+-dependent system (Ki = app. 7 microM v. 950 microM). Fluphenazine inhibited both PL/Ca2+- and CaM/Ca2+-dependent protein kinases with equal potency, as did dibucaine. Inhibition by polymyxin B of PL/Ca2+-dependent phosphorylation could be overcome by increased amounts of phosphatidylserine. Low concentrations (10(-5)M) of polymyxin B completely inhibited carbachol-stimulated amylase release from intact pancreatic acini. These results indicate that polymyxin B may be useful in delineating the relative roles of PL/Ca2+-dependent and CaM/Ca2+-dependent protein phosphorylation in biological systems and suggest a potential role for the PL/Ca2+-activated kinase in regulation of pancreatic exocrine function.
mesh_terms: D000681:Amylases / Q000378:metabolism; D000818:Animals; D002147:Calmodulin / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005476:Fluphenazine / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D010179:Pancreas / Q000201:enzymology* / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D010766:Phosphorylation; D011112:Polymyxin B / Q000494:pharmacology*; D011113:Polymyxins / Q000494:pharmacology*; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity
chemical_list: D002147:Calmodulin; D010718:Phosphatidylserines; D010743:Phospholipids; D011113:Polymyxins; D047428:Protein Kinase Inhibitors; D002217:Carbachol; D011494:Protein Kinases; D000681:Amylases; D011112:Polymyxin B; D005476:Fluphenazine