Figure 9.

Ca²⁺ increases RGS17-stimulated GTP hydrolysis. A GTPase-Glo assay was used to detect and quantify RGS-stimulated GTP hydrolysis on a rate-altered Gα_i1 mutant, Gα_i1 R178M/A326S. A, RGS17 increases the rate of GTP hydrolysis in the presence (red squares) or absence (blue circles) of saturating CaCl₂. Addition of CaCl₂ significantly decreased the K_m (Table 2). B, RGS4 stimulates GTP hydrolysis on Gα_i1 but is insensitive to the presence of CaCl₂. Data represents the mean of four independent experiments ±S.E. (error bars).