INHIBITION OF (NA+,K+)ADENOSINE TRIPHOSPHATASE AND ITS PARTIAL REACTIONS BY QUERCETIN

The bioflavonoid, quercetin, inhibited the (Na+,K+)ATPase purified from the electric organ of electric eel (Electrophorus electricus) or from lamb kidney. An analysis of its mode of action revealed that the formation of phosphoenzyme from Pi but not from ATP was inhibited. Quercetin increased the amount of ADP-sensitive phosphoenzyme (E1-P), indicating an inhibition of the conversion of E1-P to the ADP-insensitive form (E2-P). The rate of dephosphorylation of the phosphoenzyme formed from ATP was slowed by quercetin. Quercetin may inhibit the formation of E2-P from either Pi or E1-P as well as the hydrolysis of the phosphoenzyme. Its mode of action is therefore different from that of ouabain and other inhibitors of the (Na+,K+)ATPase.