Regulation of secretion from the adrenal medulla. Evidence for adenylate cyclase activity in secretory vesicle membranes

Adenylate cyclase activity was found in purified secretory vesicle membranes from the adrenal medulla. Activity was detected both by formation of radioactive cAMP from [α ³²P]ATP and by the competitive protein binding assay for cAMP. Activity was highest at pH 8.0 to 8.5, and was stimulated by sodium fluoride and guanyl 5' yl imidodiphosphate (GppNHp), a GTP analogue known to stimulate adenylate cyclase activity in plasma membrane preparations. The reaction rate was strongly dependent on the molar ratio of Mg²⁺:ATP in the system. This is the first demonstration of adenylate cyclase in a secretory vesicle membrane.