Figure 5.

The rate of activation of PMCA by CaM is not affected by dilution. Panel A: ATP hydrolysis by PMCA was measured continuously by the procedure of Webb [11]. Upon addition of calmodulin the data were fitted by the following equation:

$$\text{Y}(\text{t})={\text{Y}}_0-{\text{v}}_{\text{c}}/\text{k}+({\text{v}}_{\text{0}}+{\text{v}}_{\text{c}})\text{t}+({\text{v}}_{\text{c}}/\text{k})exp(-\text{k\hspace{0.17em}t})$$ (3)

where Y₀ is the amount of product present at time = 0, v₀ is the ATPase activity in the absence of calmodulin, v_c is the increase in activity upon calmodulin addition, and k (app k in the figure) is the rate constant for the change in activity. A detailed justification for this equation is provided in ref. [19]. Panel B: k for the different conditions presented as bar graphs.