Figure 3. CaM-dependence of the incorporation of [¹²⁵I]TID-PC/16 to PMCA4 (●) and PMCA2 (○).

Incorporation of [¹²⁵I]TID-PC/16 was determined in a medium containing 100 μM Ca²⁺ at 37°C. Eqn (2) $\left\{[{\text{PC}}_{\mathrm{B}}]=[{\text{PC}}_{min}]+\frac{[{\text{PC}}_0]-[{\text{PC}}_{min}]}{1+{\left(\frac{K_{\mathrm{d}(\text{CaM})}}{[\text{CaM}]}\right)}^n}\right\}$ was fitted to the experimental points, where [PC_B] is the percentage relative to EGTA condition of [¹²⁵I]TID-PC/16 bound to PMCA at a given concentration of CaM; [PC_min] is the minimal amount (%) of [¹²⁵I]TID-PC/16 bound to PMCA (at saturating concentration of CaM), [PC₀] is the maximal amount (%) of PC bound to PMCA (at zero [CaM]) and K _d(CaM) is the concentration of CaM for half-maximal binding to PMCA. This resulted in the following values: [PC_min] = 79.9 ± 1.9 %, [PC₀] = 154.5 ± 2.2 %, n = 3.3 ± 0.4 and K _d(CaM) = 17.6 ± 0.9 nM for PMCA4; and [PC_min] = 91.8 ± 0.9 %, [PC₀] = 123.2 ± 1.4 %, n = 1.4 ± 0.6 and K _d(CaM) = 0.52 ± 0.08 nM for PMCA2.