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Adenylate Cyclase of Torpedo Synaptosomes Is Inhibited by Calcium and Not Affected by Muscarinic Ligands
Author(s) -
Pinchasi Irit,
Michaelson Daniel M.
Publication year - 1982
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1982.tb07894.x
Subject(s) - cyclase , adenylate kinase , muscarinic acetylcholine receptor , torpedo , muscarinic acetylcholine receptor m5 , gtp' , calmodulin , chemistry , trifluoperazine , biochemistry , g protein , acetylcholine receptor , receptor , biology , biophysics , muscarinic acetylcholine receptor m3 , enzyme
Cholinergic synaptosomes isolated from the electric organ of Torpedo contain membrane‐bound adenylate cyclase activity (∼6 pmol/mg proteidmin), which is dependent on the presence of guanine nucleotides. The activity is strongly dependent on temperature and only slightly affected by NaCl. The Torpedo adenylate cyclase is completely inhibited by low levels of free Ca 2+ (K 0 ∼ 0.5 μ M ). This effect is not altered by either trifluoperazine or addition of exogenous calmodulin. Ca 3+ has no effect on the activation step of the adenylate cyclase by guanyl‐5′‐yl imidodiphosphate (GppNHp), and Mn 2+ abolishes the Ca 2+ ‐dependent inhibition of cyclic AMP synthesis. These findings suggest that Ca 2+ exerts its effect by direct interaction with a site located on the catalytic subunit. Torpedo synaptosomes contain presynaptic inhibitory muscarinic receptors. The binding of muscarinic agonists to the receptors is modulated (to lower affinity) by GTP. However, muscarinic ligands, examined under a variety of assay conditions, have no effect on adenylate cyclase activity. These results suggest that although both the muscarinic receptor and the adenylate cyclase are coupled to G proteins, they either interact with different G proteins or are situated in different regions of the presynaptic membrane.