title: Protein phosphorylation in pancreatic islets: evidence for separate Ca2+ and cAMP-enhanced phosphorylation of two 57,000 Mr proteins.
abstract: There is a phosphopeptide that has an Mr of 53,000 to 60,000 in insulin-secreting tissues and there is general agreement that this peptide can be phosphorylated in a calcium-dependent manner. The present report shows that there are at least two phosphoproteins with Mr's near 57,000 in rat pancreatic islet cytosol. One peptide has an Mr of 57,000, a pl of 7.5 - 8 and is phosphorylated in a Ca2+-enhanced manner, and the other has an Mr of 54,000, a pl of 5 - 5.5 and is phosphorylated in a cAMP-enhanced manner, as judged by two-dimensional polyacrylamide gel electrophoresis. Sepharose 4B chromatography indicated that the former polypeptide resides in a native protein complex that has an Mr of about 500,000 and the latter in a complex that has an Mr of about 180,000. Tritiated azido cyclic AMP binds to an islet polypeptide that has an Mr of 54,000. The results suggest that Ca2+ and cAMP could regulate stimulus-secretion coupling in pancreatic islets via protein phosphorylation.
mesh_terms: D000345:Affinity Labels / Q000378:metabolism; D000818:Animals; D001386:Azides / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology*; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D003600:Cytosol / Q000378:metabolism; D007515:Islets of Langerhans / Q000378:metabolism*; D007526:Isoelectric Point; D008970:Molecular Weight; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats
chemical_list: D000345:Affinity Labels; D001386:Azides; D010750:Phosphoproteins; C017042:8-azidoadenosine-3',5'-monophosphate; D000242:Cyclic AMP; D002118:Calcium