Calcium-dependent adenylate cyclase from rat cerebral cortex. Reversible activation by sodium fluoride.

The adenylate cyclase activity of a particulate preparation of rat cerebral cortex is comprised of two contributing components, only one of which requires a Ca’+-dependent regulator protein (CDR) for activity. The CDR-dependent component was stabilized by CDR. responded to increasing free Ca’+ concentrations biphasically (activation then inhibition), and was inhibited by high ratios of Mg’+ to Ca’+ and by chlorpromazine (0.1 to 0.5 m&. This component, which represented approximately 80% of the basal activity of a cortex homogenate, was completely deactivated by the removal of CDR during the preparation of the particulate fraction. Adenylate cyclase activity which was not dependent on CDR was inhibited with increasing free Ca’+ concentrations, had elevated activity at high ratios of Mg’+ to Ca”, and was not affected by chlorpromazine (0.1 to 0.5 mx). The CDR-dependent component was activated 50 to 100% by 5 rnM NaF. Activation required the presence of Ca”, was facilitated by warming to 37”, and was immediately and completely reversed by assaying with or washing with ethylene glycol bis(P-aminoethyl ether)N,N’-tetraacetic acid (EGTA). Alternately, the component which did not respond to CDR was activated 4to &fold by F. This activation was not influenced by Ca’+ or CDR and was not reversed by EGTA. Total adenylate cyclase activity of the particulate preparation was activated approximately S-fold by Fwhen Ca’+ and CDR were present. Each component when fully activated by Fcomprised about half of the overall activity. Pretreatment of the preparation with Ca’+ and CDR for 1 h at 37” resulted in the selective inactivation of enzyme which was not dependent on CDR. The remaining adenylate cyclase activity was loto 30-fold dependent on CUR and retained the characteristics of the CDR-dependent component of the original preparation.