Evidence for an Adenylate-Cyclase Activity in Neurosecretory Granule Membranes from Bovine Neurohypophysis

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Abstract
Purified bovine neurosecretory granules and their corresponding membranes were prepared after fractionation and purification processes from bovine pituitaries. An adenylate cyclase activity was detected both in the granules (apparent Km= 0.5 mM) and the corresponding preparations of the membranes (apparent Km= 0.5 mM). This enzyme was activated by fluoride in a way markedly dependent on the concentration of this ion, and with a maximum for a concentration of F−= 3.5 mM. The cyclase activity was also significantly enhanced by GTP. The reaction rate showed a strong dependance on the molar ratio [Mg2+]/[ATP] with maximal velocity for 7. It is suggested that this activity might play an important role in the control and regulation of neurosecretion in the neurohypophysis.