CATALYTIC PROPERTIES OF PURIFIED CA2+,MG2+-ATPASE OF MYOMETRIAL SARCOLEMMA

The catalytic properties of Ca2+,Mg2+-ATPase of the myometrial sarcolemma, purified from a solubilisate of the plasma membranes by affinity chromatography on calmodulin-Sepharose, were studied. It was established that the enzyme isolated in the presence of azolectin possesses high affinity for Ca2+ (Km = 0.17-mu-M), independent of the presence of calmodulin. Purified Ca2+Mg2+-ATPase possesses strict substrate specificity, is inhibited by low concentrations of orthovanadate, and is unchanged in the presence of oxytocin and prostaglandins E2 and F2-alpha. The enzyme exhibits maximum activity at the temperature 45-degrees-C, pH 7.5-8.0, concentration of Mg-ATP 1.5-2.5 mM, and Ca2+ 5-20-mu-M.