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 Gsα (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+).