Effects of Pb++ and other divalent cations on ouabain binding to E. electricus electroplax (Na+ + K+) -adenosinetriphosphatase

Siegel, G.J.; Fogt, S.K.

Molecular Pharmacology 15(1): 43-48

1979


ISSN/ISBN: 0026-895X
PMID: 218092
Accession: 068524477

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Abstract
PbCl2 reduces the level of [3H]ouabain binding to (Na+ + K+)-ATPase in Electrophorus electricus electroplax microsomal preparations in the presence of Mg2+ and ATP with or without Na+. The inhibition is competitive with ATP, and Na+ is cooperative with Pb2+ in reducing the affinity for ATP at a site involved in ouabain binding. The ATP site involved in ouabain binding is not the substrate site since no such cooperative interactions among Pb2+, Na+, and ATP could be observed with regard to phosphorylation or inhibition of hydrolysis. ADP also stimulates ouabain binding, which is inhibited competitively by Pb2+. Cd2+, Cu2+, Hg2+ and Zn2+ also inhibit ouabain binding in the presence of Mg2+, ATP, with or without 50 mM Na+ but only the inhibition by Cd2+ is potentiated by 50 mM Na+, BaCl2, FeCl2, CaCl2, MnCl2, NiCl2, CoCl2, and SrCl2 at concentrations of 60 mM did not inhibit drug binding.