Effect of different CaM species on the activity of PDE1.

<p>(<i>A</i>) The cyclic nucleotide PDE1 activity was assayed in the absence (<i>None</i>) and presence of the indicated CaM species (1.9 μM) in the presence of 100 μM free Ca²⁺ as described in Materials and Methods. The plot presents the average ± SEM of triplicate samples from three separate experiments (** p = 0.02 using the Student’s t test). (<i>B</i>) The plots present the PDE1 activity assayed as in <i>A</i> but using increasing concentrations of the indicated CaM species. (<i>C</i>) The plot presents the average ± SEM activity of PDE1 of three independent experiments assayed at increasing concentrations of non-phosphorylated CaM (<i>open symbols</i>) or phospho-(Y)-CaM (<i>filled symbols</i>) prepared as described in Materials and Methods. (<i>D</i>) The plot presents the PDE1 activity assayed as in <i>A</i> in the presence of the indicated CaM species (1.9 μM) at increasing concentrations of free Ca²⁺ using an EGTA/Ca²⁺ buffer as described in Materials and Methods. (<i>E</i>) The plot presents the average ± range activity of PDE1 assayed in the presence of non-phosphorylated CaM (<i>open symbols</i>) and phospho-(Y)-CaM (<i>filled symbols</i>) (0.97 μM) of two independent experiments assayed at increasing concentrations of free Ca²⁺ using an EGTA/Ca²⁺ buffer as described in Materials and Methods.