Evidence of a dissociable protein subunit required for calmodulin stimulation of brain adenylate cyclase

An adenylate cyclase [ATP pyrophosphate lyase (cyclizing), EC 4.6.1.1] preparation that is not stimulated by NaF,5'-guanylyl imidodiphosphate, or Ca²⁺-calmodulin has been isolated from bovine cerebral cortex by Affi-Gel Blue chromatography and calmodulin-Sepharose chromatography. Sensitivity to these effectors was restored by incubation of the adenylate cyclase preparation with detergent-solubilized protein from bovine cerebral cortex. Reconstitution of Ca²⁺ calmodulin activation required the presence of 5'-guanylyl imidodiphosphate. The factor required for restoration of Ca²⁺ calmodulin stimulation was sensitive to heat, trypsin digestion, and N-ethylmaleimide. These observations suggested that this adenylate cyclase activity requires the presence of one or more guanyl nucleotide binding subunits for calmodulin sensitivity.