FIGURE 9.

PMCA conformational change induced by G-actin measured as the relative incorporation of [¹²⁵I]TID-PC/16 to PMCA. A, purified human erythrocyte PMCA was incubated with [¹²⁵I]TID-PC/16 as described under “Materials and Methods” after which purified G-actin was added at different concentrations. The reaction medium contained 70 μm Ca²⁺. After 1 min of actin addition, the reaction was stopped by exposing the samples to a UV light source. Data are the mean ± S.E. of two independent experiments. The continuous line corresponds to the best fitted parameters of Equation 3 to the experimental data. B, effect of saturating concentrations of 120 nm CaM, 10 μm phosphatidic acid, and 5 μm actin on the incorporation of [¹²⁵I]TID-PC/16 to purified PMCA. As expected for a calmodulin-like activator, the specific incorporation of [¹²⁵I]TID-PC/16 decreased with actin from near 150% to a value of 95.1 ± 2.4%, although CaM and phosphatidic acid (PA) decreased the specific incorporation to 76 ± 1 and 89 ± 2%, respectively.