Vanadate interaction with the Na, K-ATPase. An assay of serum vanadate based on the displacement of (48V) vanadate from Na, K-ATPase.

Under optimum conditions for vanadate binding to Na, K-ATPase equilibrium binding date for a range of vanadate concentrations were compiled. Scatchard plots indicated an identical binding capacity for vanadate and ouabain with conventionally prepared Na, K-ATPase batches. A method for determination of vanadate in serum based upon the high affinity of vanadate for Na, K-ATPase is described. The method takes advantage of the shift in equilibrium binding of (48V) vanadate upon addition of an aliquot of vanadate-containing serum. It is shown that the interplay between vanadate and ouabain in vanadate-facilitated ouabain binding to Na, K-ATPase leads to an enzyme-vanadate-ouabain complex to which vanadate is rather firmly bound.