Abstract

Bovine or rat brain adenylate cyclase (EC 4.6.1.1) solubilized by Lubrol PX contained an activator which was separated from the enzyme by an anionic exchange resin column. Dissociation of the activator from adenylate cyclase rendered the enzyme less active, and reconstituting with an exogenous activator restored full enzyme activity. A pure protein activator of cyclic 3′:5′-nucleotide phosphodiesterase (EC 3.1.4.17) isolated from bovine brain also stimulated this adenylate cyclase. Stimulation of adenylate cyclase by the activator required Ca++, the effect being immediate and reversible. Although the activator was specific, it lacked tissue specificity; an activator isolated from bovine brain cross-activated effectively adenylate cyclase from rat, and vice versa. These findings indicate that brain adenylate cyclase required an activator for activity and that this activator is functionally identical to the protein activator of phosphodiesterase (J.B.C. 249: 4943–4954, 1974).