Regulation of the Catalytic Unit of Adenylate Cyclase System in Rat Brain

It is well known that the adenylate cyclase system in the cell membrane consists of the ligand receptor, the guanine nucleotide-binding regulatory unit (G/F), and the catalytic unit which catalyzes the formation of cyclic AMP from ATP (1,2). As compared with the former two, the catalytic unit has been less characterized, principally because of instability of this protein after solubilization with the use of detergents. Nevertheless, many efforts have gradually clarified the nature of this protein. Among them, success in separation of the catalytic unit from G/F (3) and use of the cyc mutant of S49 lymphoma cell which apparently lacks a functional G/F protein (4) have facilitated the clarification. As a result, the molecular size of the catalytic unit has been estimated to be 170,000–220,000 in several tissues (5,6).