Concentration-dependence of RGS effects on steady-state GTPase activity. Carbachol-dependent GTPase activity was measured at multiple concentrations of RGS2 and RGS4 at free magnesium concentrations of 0.5 and 7.5 mM, as shown in Fig. 5. Data from individual dose-response curves for RGS2 and for RGS4 at 7.5 mM free magnesium were fitted to the Hill equation. RGS4 in the presence of 0.5 mM free magnesium yielded bell-shaped curves, which were individually analyzed as the sum of two rectangular hyperbolae. The parameters presented are mean values ± S.D.
| [Mg2+]free | EC50 | nH | Kup | Kdown | n | |
|---|---|---|---|---|---|---|
| mM | μM | μM | μM | |||
| RGS2 | 0.5 | 1.3 ± 0.6 | 2.6 ± 0.5 | 5 | ||
| RGS2 | 7.5 | 2.2 ± 1.2 | 3.5 ± 0.6 | 4 | ||
| RGS4 | 0.5 | 0.14 ± 0.08 | 4.0 ± 3.0 | 6 | ||
| RGS4 | 7.5 | 0.49 ± 0.07 | 1.8 ± 0.6 | 5 |