title: A calcium and calmodulin-dependent protein kinase present in differentiating Dictyostelium discoideum.
abstract: A protein kinase from Dictyostelium discoideum which phosphorylates the synthetic peptide, calmodulin-dependent protein kinase substrate (CDPKS, amino acid sequence: PLRRTLSVAA) and is stimulated by Ca2+/calmodulin is described. This is the first report of a protein kinase with these characteristics in D. discoideum. The enzyme was partially purified by Q-Sepharose chromatography. The protein kinase is very labile, and rapidly loses Ca2+/calmodulin-dependence upon standing at 4 degrees C, even in the presence of protease inhibitors, making further purification and characterisation difficult. In the active fractions, a 55 kDa polypeptide is labelled with [gamma-32P]ATP in vitro under conditions in which intramolecular rather than intermolecular reactions are favoured. The phosphorylation of this peptide is stimulated in the presence of Ca2+ and calmodulin but not Ca2+ alone. Ca2+/calmodulin-dependent stimulation is inhibited in the presence of the calmodulin antagonist, trifluoperazine (TFP). It is proposed that the 55 kDa polypeptide may represent the autophosphorylated form of the enzyme.
authors.affiliation: School of Biological Sciences, Flinders University of South Australia, Adelaide.
authors.forename: A J
authors.initials: AJ
authors.lastname: Dunbar
authors.forename: J F
authors.initials: JF
authors.lastname: Wheldrake
mesh_terms: D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000737:chemistry / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002847:Chromatography, Agarose; D004023:Dictyostelium / Q000201:enzymology* / Q000254:growth & development; D004591:Electrophoresis, Polyacrylamide Gel; D008970:Molecular Weight; D010766:Phosphorylation; D011494:Protein Kinases / Q000737:chemistry / Q000378:metabolism*; D014268:Trifluoperazine / Q000494:pharmacology
chemical_list: D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002147:Calmodulin; D011494:Protein Kinases; D014268:Trifluoperazine