Properties of the purified hypothalamic pituitary NA/K-ATPase inhibitor

Previously we described the isolation and final purification of an endogenous sodium-pump inhibitor from the CNS, mainly from bovine hypothalamus and pituitary. The purification protocol consisted of lipophilic chromatography, followed by lipid extraction, and semipreparative and analytical reverse-phase high-pressure liquid chromatography. The bioassays used were in vitro Na+/K(+)-ATPase inhibition, and 3H-ouabain displacement from its specific binding site in the enzyme structure, as well as inhibition of 86Rb uptake from human red blood cells. We have obtained, from both tissues, a low-molecular-weight, nonpeptidic, nonlipidic substance that elutes as a single peak highly pure according to criteria of coincidence of its spectra properties. When rechromatographed in two different chromatographic systems, the same homogeneous peak is obtained suggesting complete purity. This pure substance can be isolated from other bovine tissues as well as from human plasma and human placenta. It shows a very distinctive fluorescence spectrum and it behaves as a potent inhibitor of the Ca2+ pump of synaptosomal plasma membrane.