Figure 4.

Ca²⁺ differentially inhibits the activity of the different forms of ACV. (A) The forskolin (100 μM)-stimulated activities of the full-length ACV in Sf9 cell membranes, and the two soluble forms of ACV, C1-C2 and C1a-C2, in supernatants of bacterial cell lysates in the presence of various Ca²⁺ concentrations were monitored as described in Fig. 1 and Methods. Free-Ca²⁺ concentrations were determined using Calcium Green-5N dye. (B) Same as A, except that the activities of the different forms of ACV were maximally stimulated by the combination of G_sα (100 nM) and forskolin (100 μM). Values are the mean ± SEM of four determinations. Significant differences were assessed by Student’s unpaired t test analyses. ∗, P < 0.003 (as compared with controls without Ca²⁺).