Influence of dielectric permeability and incubation medium temperature on sensitivity of ATPase of contractile protein complex to eosin Y was studied on preparations of uterine smooth muscle actomyosin. It was shown, that a decrease of dielectric permeability from 74.1 to 68.8 is accompanied by inhibition of activity of actomyosin ATPase by 30%. Administration of eosin Y to the incubation medium intensifies the inhibition of activity of actomyosin ATPase, that correlates with a decrease of dielectric permeability and increase of eosin Y concentration. Catalytic titration of actomyosin ATPase by eosin Y (from 10(-7) to 10(-5) M) on the background of a change of dielectric permeability (from 741 to 68.8) shows, that curve of dependence of ATPase activity on the inhibitor concentration is characterized by a lower value of enzymatic activity and its quicker decay at D 68.8 than at D 74.1. Under a decrease of dielectric permeability from 74.1 to 68.8 the observed decrease of the value of inhibition coefficient from 0.74 +/- 0.07 to 0.10 +/- 0.01 MKM, that can evidence for the essential role of electrostatic interactions in the binding of eosin Y with smooth muscle actomyosin. Studies of energy aspects of the mechanism of an eosin Y action on ATP-hydrolase activity of smooth muscle contractive proteins (determination of temperature dependence and activation energy E(o)) show that the inhibitory effect of eosin Y on myometrium actomyosin ATPase activity is connected with an increase of the reaction energy barrier. That is, the effect of eosin Y on actomyosin ATPase activity is shown not only on catalytic but also on thermodynamic levels.