title: Characterization of an ATP-Mg2+-dependent guanine nucleotide-stimulated adenylate cyclase from Neurospora crassa.
abstract: A novel adenylate cyclase activity was found in crude homogenates of Neurospora crassa. The adenylate cyclase had substantial activity with ATP-Mg2+ as substrate differing significantly from the strictly ATP-Mn2+-dependent enzyme characterized previously. Additionally, the ATP-Mg2+-dependent activity was stimulated two- to fourfold by GTP or guanyl-5'-yl-imido-diphosphate (Gpp(NH)p). We propose that the ATP-Mg2+-dependent, guanine nucleotide-stimulated activity is due to a labile regulatory component (G component) of the adenylate cyclase which was present in carefully prepared extracts. The adenylate cyclase had a pH optimum of 5.8 and both the catalytic and G component were particulate. The Km for ATP-Mg2+ was 2.2 mM in the presence of 4.5 mM excess Mg2+. Low Mn2+ concentrations had no effect on adenylate cyclase activity whereas high concentrations of Mn2+ or Mg2+ stimulated the enzyme. Maximal Gpp(NH)p stimulation required preincubation of the enzyme in the presence of the guanine nucleotide and the K1/2 for Gpp(NH)p stimulation was 110 nM. Neither fluoride nor any of a variety of glycolytic intermediates or hormones, including glucagon, epinephrine, and dopamine, had an effect on ATP-Mg2+-dependent adenylate cyclase activity. However, the enzymatic activity was stimulated not only by GTP but also by 5'-AMP and was inhibited by NADH.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000262:Adenylyl Cyclases / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D006150:Guanine Nucleotides / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000494:pharmacology*; D009491:Neurospora / Q000201:enzymology*; D009492:Neurospora crassa / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D006150:Guanine Nucleotides; D000255:Adenosine Triphosphate; D000262:Adenylyl Cyclases; D008274:Magnesium