title: Actin-activated Mg-ATPase activity of Dictyostelium myosin II. Effects of filament formation and heavy chain phosphorylation.
abstract: The actin-activated Mg-ATPase activities of unphosphorylated and heavy chain phosphorylated Dictyostelium myosin II and of a Dictyostelium myosin II heavy meromyosin (HMM) fragment were examined at different Mg2+ and KCl concentrations. The Mg-ATPase activity of HMM displayed a maximum rate, Vmax, of about 4.0/s and a Kapp (actin concentration required to achieve 1/2 Vmax) that increased from 8 to 300 microM as the KCl concentration increased from 0 to 120 mM. When assayed with greater than 5 mM Mg2+ and 0 mM KCl the unphosphorylated Dictyostelium myosin II yielded a Kapp of 0.25 microM and a Vmax of 2.8/s. At lower Mg2+ concentrations or with 50 mM KCl the data were not fit well by a single hyperbolic curve and Kapp increased to 25-100 microM. The increase in Kapp did not correlate with the loss of sedimentable filaments. At KCl concentrations above 100 mM Vmax increased to greater than 4/s. Heavy chain phosphorylated myosin (3.5 mol of phosphate/mol myosin) displayed a Vmax of about 5/s and a Kapp of 50 microM under all conditions tested. Thus, heavy chain phosphorylation inhibited the actin-activated Mg-ATPase activity of Dictyostelium myosin II in 5-10 mM Mg2+ and low ionic strength through an increase in Kapp.
authors.affiliation: Department of Biochemistry, Queen's University, Kingston, Ontario, Canada.
authors.forename: T
authors.initials: T
authors.lastname: Truong
authors.forename: Q G
authors.initials: QG
authors.lastname: Medley
authors.forename: G P
authors.initials: GP
authors.lastname: Côté
mesh_terms: D000199:Actins / Q000378:metabolism* / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D004023:Dictyostelium / Q000378:metabolism*; D004789:Enzyme Activation; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009218:Myosins / Q000378:metabolism*; D009994:Osmolar Concentration; D010766:Phosphorylation; D011189:Potassium Chloride / Q000494:pharmacology
chemical_list: D000199:Actins; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase; D009218:Myosins; D008274:Magnesium