Endogenous substrate proteins for Ca2+-calmodulin-dependent, Ca2+-phospholipid-dependent and cyclic AMP-dependent protein kinases in mouse pancreatic islets.
The occurrence of endogenous substrate proteins for Ca2+-dependent protein kinase, augmented by either phospholipid or calmodulin, and for cyclic AMP-dependent protein kinase was examined in homogenates and subcellular fractions of mouse pancreatic islets. Islet protein phosphorylation was enhanced by Ca2+-calmodulin; the major endogenous substrates in the homogenate were two proteins of Mr 53000 and 100000. The Mr-100000 phosphoprotein was localized to a 27000g-supernatant fraction, whereas the Mr-53000 phosphoprotein was present in a 27000g particulate fraction of mouse islets. In the presence of Ca2+, phosphatidylserine stimulated phosphorylation of 15 proteins, of Mr 17000-190000, in a 27000g-supernatant fraction. No effects of Ca2+ plus phosphatidylserine were observed in a 27000g particulate fraction of mouse islets. Examination of cyclic AMP-dependent protein phosphorylation revealed five substrate proteins, of Mr 23000-72000, present in the 27000g supernatant of mouse islets. No common substrates for either the two Ca2+-dependent phosphorylation systems or for the cyclic AMP-dependent and the Ca2+-calmodulin-dependent phosphorylation systems were noted. On the other hand, the actions of the cyclic AMP-sensitive and the Ca2+-phospholipid-sensitive systems may be overlapping, since two common substrates for them were noted in the 27000g-supernatant fraction. The results are consistent with the hypothesis that protein phosphorylation may play a role in the regulation of insulin secretion by Ca2+ and cyclic AMP. The extensive stimulatory effect of phosphatidylserine furthermore suggests that the Ca2+-phospholipid-sensitive protein kinase may prove to be a prominent phosphorylation system in pancreatic islets.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D003600:Cytosol / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000201:enzymology*; D008297:Male; D051379:Mice; D010718:Phosphatidylserines / Q000494:pharmacology; D010766:Phosphorylation; D011493:Protein Kinase C; D011494:Protein Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology
D002147:Calmodulin; D010718:Phosphatidylserines; D011506:Proteins; D000242:Cyclic AMP; D011494:Protein Kinases; D011493:Protein Kinase C; D002118:Calcium