Studies on the Adrenocorticotropic Hormone-activated Adenyl Cyclase of a Functional Adrenal Tumor

An adrenocorticotropic hormone (ACTH)-sensitive, steroid-producing mouse adrenal tumor was homogenized and fractionated by differential centrifugation. The adenyl cyclase activity that was stimulated by ACTH and by fluoride was purified 10- to 20-fold and localized to particulate fractions. The enzyme activity was not affected by several other polypeptide hormones, by epinephrine, or by prostaglandin PGE 1 . The ACTH-induced increase in adenyl cyclase activity was maximal at pH 7.4 to pH 7.7. The optimal Mg 2+ :ATP ratio was 1 to 1.5. Enzyme activity in the presence of ACTH was decreased by Ca 2+ , Na + , K + , and propranolol. Other nucleotides at equimolar concentrations to ATP also decreased the ACTH effect to a variable extent; dATP was the most effective inhibitor.