title: Modulation of the response of bovine adrenocortical adenylate cyclase to corticotropin.
abstract: An assessment was made of some of the basic parameters responsible for the modulation of adenylate cyclase activity in a bovine adrenocortical plasma-membrane preparation. When determined at 0.1 mM-ATP, basal adenylate cyclase activity increased with increasing MgCl2 concentrations, whereas in the presence of corticotropin activity was essentially maximal at 10mM-MgCl2; high concentrations (25mM) of MgCl2 inhibited adenylate cyclase activity determined in the presence of both corticotropin and GTP. At all MgCl2 concentrations, corticotropin and GTP activated the enzyme in a synergistic fashion. The magnitude of the stimulation of basal activity produced by corticotropin was a function of Mg2+ concentration, whereas that produced by GTP appeared largely independent of Mg2+ concentration. Adenylate cyclase activity in the bovine adrenal membrane was half-maximally stimulated by corticotropin concentrations in the range 0.3--1.0 nM. The concentration of corticotropin evoking half-maximum response was not significantly affected by raising the free Mg2+ concentration from 0.4 to 4.9 mM, nor by the presence of GTP. In the presence of GTP, high concentrations (over 1 micrometer) of corticotropin inhibited adenylate cyclase activity, although no inhibition was apparent in the absence of guanine nucleotide.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000302:Adrenal Cortex / Q000187:drug effects / Q000201:enzymology*; D000324:Adrenocorticotropic Hormone / Q000494:pharmacology*; D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000201:enzymology; D003366:Cosyntropin / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology
chemical_list: D003366:Cosyntropin; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D000324:Adrenocorticotropic Hormone; D000262:Adenylyl Cyclases; D008274:Magnesium