title: Characterization of phosphotyrosyl-protein phosphatase activity associated with calcineurin.
abstract: Calcineurin purified from bovine brain is shown to possess phosphotyrosyl -protein phosphatase activity towards proteins phosphorylated by the epidermal growth factor receptor/kinase. The phosphatase activity is augmented by Ca2+/calmodulin or divalent cation (Ni2+ greater than Mn2+ greater than Mg2+ greater than Co2+). In the simultaneous presence of all three effectors, the enzymatic activity is synergistically increased. Ca2+/calmodulin activates the Mg2+-supported activity by decreasing the Km value for phosphotyrosyl -casein from 2.2 to 0.6 microM, and increasing the Vmax from 0.4 to 4.6 nmol/min/mg. These results represent the first demonstration that calcineurin can dephosphorylate phosphotyrosyl -proteins and suggest a novel mechanism of activation of this enzyme.
mesh_terms: D000818:Animals; D001921:Brain / Q000201:enzymology; D002118:Calcium / Q000502:physiology; D002147:Calmodulin / Q000502:physiology; D002148:Calmodulin-Binding Proteins; D002417:Cattle; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D007700:Kinetics; D008274:Magnesium / Q000502:physiology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation
chemical_list: D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D010749:Phosphoprotein Phosphatases; D008274:Magnesium; D002118:Calcium