Interaction of digitoxigenin with lecithin membranes.

The binding of digitoxigenin to lecithin model membranes was investigated by application of electron spin- and nuclear magnetic resonance methods. A digitoxigenin spin-label derivative was found to bind specifically to the pseudohexagonal rigid lattice of lecithin membranes. The binding is accomplished by some of the structural features which are required for the biological activity of cardiac glycosides. Digitoxigenin has a procooperative effect on dipalmitoyl-lecithin membranes. The induction of lipid phase separation is discussed as a hypothetic molecular mechanism of action of cardiac glycosides on biological membranes.