[Effect of incubation medium dielectric permeability on enzymatic activity of functionally different ATPases of...

Some organic solvents (2-10%) have been comparatively studied for their effect on purified transporting Ca2+, Mg(2+)-ATPase, solubilized from the plasma membrane of smooth muscle cells and on actomyosine ATPase of the smooth muscle. The inhibiting effect of solvents on the initial maximum specific activity of Ca2+, Mg(2+)-ATPase corresponds to the sequence dioxane > acetone > ethanol > dimethyl sulfoxide (DMSO). Like the case with Ca2+, Mg(2+)-ATPase, dioxane inhibits actomyosine ATPase; acetone, ethanol and DMSO stimulate ATP-hydrolase reaction which is catalyzed by the complex of contractile proteins. It is proved that the effect of the decrease of ATPase activity with decrease of incubation medium polarity is exceptionally determined by the value of incubation medium the dielectric permeability. This effect is independent of chemical nature of organic solvents which were used with the aim to obtain the corresponding values of D. It is supposed that the cause of activity inhibition of solubilized transporting Ca2+, Mg(2+)-ATPase under the effect of dioxane, acetone, ethanol and inhibition of activity of actomyosine ATPase as affected by dioxane is mainly connected with the increase of electrostatical interaction between opposity charged active centre of ATPase and the product (products) of ATP-hydrolase reaction (Mg ADP-, HPO4(2-)), which is induced by the decrease of incubation medium polarity (the decrease of D value). Stimulating effect of acetone and ethanol on actomyosine ATPase is probably determined by superposition of two components: that connected with direct effect of these solvents on the protein catalyst (interaction with enzyme with the future break of hydrogen and hydrophobic bonds in the protein and its "fluffing") and "electrostatic component" determined by the change of D value of the incubation medium. Possible role of electrostatic interactions between ATPases and reagents as the factor of non-specific control of catalytic activity of these enzymes is discussed.