Mechanism of eosin Y action of activity of solubilized Ca2+, Mg2+- ATPase from smooth muscle sarcolemma

The eosin Y inhibitory effect on the activity of smooth muscle plasma membrane Ca(2+)-transporting ATPase was studied: effect of this inhibitor on the maximal initial rate of ATP-hydrolase reaction, catalyzed by Ca2+, Mg(2+)-ATPase, on the affinity of enzyme for the reaction reagents (Ca2+, Mg2+, ATP). Dependence of eosin Y inhibitory effect on some physicochemical factors of incubation medium was studied too. It was determined that eosin Y inhibited reversibly and with high specificity purified Ca2+, Mg(2+)-ATPase solubilized from myometrial cell plasma membrane (Ki--0.8 microM), decreased the turnover rate of this enzyme determined both by Mg2+, ATP and Ca2+. This inhibitor had no effect on the enzyme affinity for Ca2+, increased affinity for Mg2+ and decreased affinity for ATP. It was determined that inhibition of Ca2+, Mg(2+)-ATPase by eosin Y depended on pH and dielectric permeability of the incubation medium: increasing of pH from 6.5 to 8.0 reduced the apparent Ki, decreasing of dielectric permeability from 74.07 to 71.19 increased the apparent Ki.