Calmodulin Regulation of Cyclic AMP Metabolism

Calmodulin is a relatively small regulatory protein which mediates many Ca2+ effects, including the stimulation of brain adenylate cyclase and Ca2+-sensitive phosphodiesterase. In both cases, calmodulin forms a complex with the apoenzyme in the presence of Ca2+ . The Ca2+-sensitive phosphodiesterase is a tetramer comprised of two catalytic and two calmodulin subunits. Brain may contain distinct forms of adenylate cyclase, one calmodulin-sensitive and another calmodulin-insensitive. Neither form has been vigorously characterized, and the relationship between the two forms remains to be established.