Interaction of glucocorticoid hormones with mitochondrial membranes

The mechanism of 3H glucocorticoid binding with the rat liver mitochondria in vitro is investigated. The linear dependence of the amount of bound hormones on the concentration of the free ones is shown and no saturation in the region of the physiological concentrations is observed. A very low specific binding in the presence of a 100-fold excess of an unlabelled hormone is found. The outer mitochondrial membranes binds a considerably higher amount of steroids, than the inner one. The binding of steroids with the intact liver mitochondria is 2-3 times higher as compared to the binding with spheroplasts of Escherichia coli. Delipidization of mitochondria by diverse lipotropic agents differently influences the binding of steroids with the different functional groups. The interaction of steroids with mitochondria depends on the osmolarity of the incubation medium: the binding is 1.5-3 times higher in the isotonic sucrose solution, that in the hypo- or hypertonic ones. A conclusion is made about the nonspecific character of glucocorticoid binding with mitochondria caused by the interaction with hydrophobic compounds of the mitochondrial membranes. The possible chemical mechanisms for such an interaction are discussed.