title: Characterization of a bovine brain magnesium-dependent phosphotyrosine protein phosphatase that is inhibited by micromolar concentrations of calcium.
abstract: In this study a rho-nitrophenyl phosphate (PNPP) phosphatase was purified 476-fold from bovine brain cytosol. The molecular weight of the enzyme is 84,000 as determined by gel filtration. The PNPP phosphatase could also dephosphorylate [32P-Tyr]-casein and -poly (Glu, Tyr). [32P-ser]-casein and -histone were not substrates. The phosphatase activity was found to be totally dependent on divalent metal ions. Mg2+ was the most effective with Ka of 20 microM. Ca2+ was found to be a potent inhibitor of the phosphatase. Using PNPP as a substrate the IC50 for Ca2+ was 0.6 microM. Several known inhibitors of phosphotyrosyl protein phosphatases such as Zn2+, vanadate, and molybdate also inhibited the PNPP phosphatase. The very high sensitivity for inhibition by Ca2+ suggests that the activity of the phosphotyrosyl protein phosphatase may be regulated by fluctuations in the intracellular concentrations of Ca2+.
authors.affiliation: Department of Biology, University of Waterloo, Ontario, Canada.
authors.forename: T J
authors.initials: TJ
authors.lastname: Singh
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002118:Calcium / Q000494:pharmacology*; D002413:Cations, Divalent; D002417:Cattle; D002848:Chromatography, DEAE-Cellulose; D003600:Cytosol / Q000201:enzymology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D017027:Protein Tyrosine Phosphatases
chemical_list: D002413:Cations, Divalent; D010749:Phosphoprotein Phosphatases; D010744:Phosphoric Monoester Hydrolases; D009597:4-Nitrophenylphosphatase; D017027:Protein Tyrosine Phosphatases; D008274:Magnesium; D002118:Calcium