Structural basis of steroid compounds interaction with "digitalis"-receptor sites of Na,K-dependent ATPase.

Twenty-two Steroid molecules have been tested for the inhibition Na,K-dependent ATPase at 10(-7)-10(-4) M concentrations. At the 10(-5) M concentration of the investigated molecules, inhibition ranged from 8 to 36%. To explain the structure-inhibition % relationship, we determined the value of heteropolarity or biphilicity moment of these molecules. This value would appear to be dependent on the space location and hydrophilicity of the molecule elementary fragments, and to the degree of their water accessibility; however, it is independent of the hydrophilicity of the molecules as a whole. On the basis of the obtained data, details of Na,K-ATPase digitalis-receptor structure and the mechanism of the glycoside-receptor interaction are discussed.