title: Calcium inhibition of a heat-stable cyclic nucleotide phosphodiesterase from Neurospora crassa.
abstract: Neurospora crassa had a heat-stable (up to 95 degrees C), soluble cyclic nucleotide phosphodiesterase (PDE). Both unheated and heat-stable PDE activities were inhibited by micromolar concentrations of Ca2+. This inhibition was reversed by EGTA or EDTA in molar excess of the Ca2+ concentration. Calmodulin was not involved in the Ca2+ inhibition, nor was Ca2+ inhibition of the heat-stable PDE due to cleavage inactivation of the enzyme by a Ca2+-stimulated protease. In addition to Ca2+, several other cations inhibited the activity of the heat-stable enzyme. Cyclic AMP and cGMP, but not 2'3' cAMP were substrates for both unheated and heat-stable PDEs. This is the first report of a PDE which is inhibited by micromolar concentrations of Ca2+.
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000302:isolation & purification; D002412:Cations / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006358:Hot Temperature; D009491:Neurospora / Q000201:enzymology*; D009492:Neurospora crassa / Q000201:enzymology*
chemical_list: D002147:Calmodulin; D002412:Cations; D004533:Egtazic Acid; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D002118:Calcium