FIGURE 9.

Vanadate dependence of Na⁺,K⁺-ATPase activity. The rate of ATP hydrolysis was determined at 37 °C in 30 mm histidine (pH 7.4), 130 mm NaCl, 20 mm KCl, 3 mm MgCl₂, 3 mm ATP, 1 mm EGTA, 10 μm ouabain, and the indicated concentrations of vanadate. Filled circle, wild type; crossed circle, ΔY; filled triangle pointing upward, ΔTYY; dotted triangle pointing upward, ΔWVEKETYY; open square, EKE-AAA; crossed square, K768A; filled square, K768M; dotted triangle pointing downward, YY-AA. Each line shows the best fit of the Hill equation, and the extracted K_0.5(vanadate) values for vanadate inhibition are indicated in Table 1.