Adenyl cyclase activity has been studied in a particle fraction prepared from fat cells which consists in the main of smooth membrane fragments. These preparations can be stored for at least 2 weeks at —80° without significant loss of cyclase activity or diminution of responsiveness to epinephrine. Cyclase activity was assayed as described by Chase and Aurbach using α-32P- or 3H-labeled adenosine triphosphate. Maximal activity (basal and hormone or NaF stimulated) was observed at pH 8.0 which was used in all assays. Values for cyclase activity assayed by this procedure agreed closely with those obtained when cyclic 3′,5 ′adenosine monophosphate accumulation was quantified in a bioassay. Under the conditions of the assay, about 10% of 0.5 mamole of 3Hlabeled 3′,5′-adenosine monophosphate was degraded. Maximal adenyl cyclase activities were observed in the presence of 3 mM NaF. Activity was less with higher concentrations. Adenyl cyclase activity was enhanced, usually to different maximal levels, by epinephrine, adrenocorticotropin or glucagon. The relative effectiveness of the three hormones varied in different preparations. The effect of epinephrine was prevented by the α-adrenergic blocking agents, dichloroisoproterenol and pronethalol, which themselves enhanced cyclase activity. No effects of insulin or prostaglandin E1 on basal or epinephrine-stimulated cyclase activity could be demonstrated. © 1969, American Chemical Society. All rights reserved.
