[Kinetic uniformity of the ATP hydrolysis reaction catalyzed by Mg2+-ATPase in smooth muscle cell membrane].
The kinetic properties of Mg(2+)-ATPase (EC 3.6.1.3) from myometrium cell plasma membranes have been studied. Under conditions of enzyme saturation with ATP (0.5-1.0 mM) or Mg2+ (1.0-5.0 mM) the initial maximal rates of the Mg(2+)-dependent enzymatic ATP hydrolysis, V0 ATP and V0 Mg, are 27.4 +/- 3.3 and 25.2 +/- 4.1 mumol Pi/hour/mg of protein, respectively. The apparent Michaelis constant, Km, for ATP and of the apparent activation constant, K alpha, for Mg2+ are equal to 28.1 +/- 2.6 and 107.0 +/- 26.0 microM, respectively. The bivalent metal ions used at 1.0 mM suppress the Mg(2+)-dependent hydrolysis of ATP whose efficiency decreases in the following order: Cu2+ > Zn2+ = Ni2+ > Mn2+ > Ca2+ > Co2+. Alkalinization of the incubation medium from pH 6.0 to pH 8.0 stimulates the Mg(2+)-dependent hydrolysis of ATP. It has been found that Mg(2+)-ATPase has the properties of an H(+)-sensitive enzymatic sensor which is characterized by a linear dependence between the initial maximal rate of the reaction, V0, and the pH value. The feasible role of plasma membrane Mg(2+)-ATPase in some reactions responsible for the control of proton and Ca2+ homeostasis in myometrium cells has been investigated.
Kosterin
S A
SA
Bratkova
N F
NF
Zimina
V P
VP
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002384:Catalysis; D002413:Cations, Divalent; D002462:Cell Membrane / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D009130:Muscle, Smooth / Q000166:cytology / Q000201:enzymology*; D013552:Swine
D002413:Cations, Divalent; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase
Kineticheskie zakonomernosti reaktsii gidroliza ATP, kataliziruemoĭ Mg2+-ATPazoĭ plazmaticheskoĭ membrany gladkomyshechnykh kletok.