Inhibition of sodium- and potassium-dependent adenosine triphosphatase by ethacrynic acid: Ligand-induced modifications

Abstract

Inhibition of phosphorylation and ATP hydrolyzing activity of(Na + + K +)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) by ethacrynic acid was facilitated by Na + or Mg 2+ plus inorganic phosphate or Na + plus Mg 2+ and ATP. The inhibition of enzyme activity was antagonized by ATP, ADP and K +. ATP with or without ouabain did not reverse the acceleration or retardation of the rate of inhibition of enzyme activity by ethacrynic acid in the presence of Na + or K +. Ouabain did not significantly alter the rate of inhibition of ATP hydrolysis and phosphorylation by ethacrynic acid, indicating that the binding sites of ouabain and ethacrynic acid are probably different. Results show ligand-induced conformational changes in (Na + + K +)-ATPase and give further support to the allosteric model for cation transport involving the formation of a phosphorylated intermediate.