Adrenal cortex adenylate cyclase. Is Ca2+ involved in ACTH stimulation?

The chelator EGTA inhibits the activation of bovine adrenal cortex adenylate cyclase by ACTH. Hormonal response is restored by addition of Ca2+, Mn2+ and other cations which are able to significantly reduce the concentration of uncomplexed EGTA in the adenylate cyclase assy medium. Time course studies reveal that the enzyme in the activated state (induced by adenylate cyclase reagents and hormone or by pretreatment with hormone) is resistant to EGTA inhibition.