Spin-labeled ouabain as a probe for cardiac glycoside receptor/Na, K-ATPase.

We have synthesized a nitroxide spin-label derivative of the cardiac glycoside, ouabain. It has been tested on purified Na,K-ATPase from dog kidney as a probe to study the physico-chemical interactions of this class of drugs with receptor(s). Spin-labeled ouabain retained the biochemical properties of native ouabain as judged by dose response curves for inhibition of Na,K-ATPase activity and inhibition of [3H]-ouabain binding to receptor. Electron paramagnetic resonance spectra of the spin-labeled ouabain-Na,K-ATPase complex revealed the presence of two types of bound label with differing degrees of immobilization.