Abstract
The activation of adenylate cyclase by NaF was dependent on the previous incubation time and the concentration of F-. The activation by F- was irreversible and Mg2+ was required for the maximum effect. Turbidity of microsome suspension was also greatly increased by F- plus Mg2+ . These effects on adenylate cyclase and membrane turbidity were specific for F- and F--saturation curves for both were similar, though Mg2+-saturation curves for both were dissimilar. The increase in turbidity induced by F- plus Mg2+ was rapidly reversed by ATP, GTP, ITP, UTP and CTP. However, ITP only, among all the triphospho-nucleotides tested, reversed the activity of adenylate cyclase previously activated by NaF plus MgCl2. The activity of the enzyme reversed by ITP was not, however, re-enhanced by the presence of NaF in the assay medium. These results suggest the possibility that F- induces a change in the membrane structure itself, and this change can be reversed by incubation with ITP. Consequently, adenylate cyclase may be conformed either to an activated or an unactivated state.
