Figure 3.

Effects of varied concentrations of ouabain and ouabain derivatives on PNPPase activity. Purified Na⁺,K⁺-ATPase was incubated at 20 μg/ml with varied concentrations of ouabain, AO, FO, and NBDO for 30 min at room temperature, and the PNPPase activity was measured as described in Methods. The data were fitted to a sigmoidal dose-response curve by using prizm 2.01 (GraphPad, San Diego). The fitted parameters and symbols are: ○ = ouabain, EC₅₀ = 6.4 nM; ● = AO, EC₅₀ = 64 nM; □ = NBDO, EC₅₀ = 210 nM; ■ = FO, EC₅₀ = 860 nM.