FIGURE 1.
Effect of vanadate (A) and lanthanum (B) on PMCA Ca2+-ATPase activity. PMCA Ca2+-ATPase activity was determined as described under “Experimental Procedures” and normalized according to the activity obtained in the absence of (VO4)3− or LaIII. The continuous line represents the fit of Equation 1 to the experimental values. The apparent Ki for the complexes of PMCA with (VO4)3− and LaIII were 1.5 ± 0.1 and 8.2 ± 0.5 μm, respectively. Insets, gel autoradiographs of the phosphorylated intermediates of PMCA obtained in the absence of vanadate (control (C)) or in the presence of 50 μm (VO4)3− (A) or 100 μm LaIII (B).