title: The dependence on Ca2+ of the guanine-nucleotide-activated polyphosphoinositide phosphodiesterase in neutrophil plasma membranes.
abstract: The requirement for Ca2+ for the activation of polyphosphoinositide phosphodiesterase was studied with the guanine nucleotide analogue guanosine 5'-[gamma-thio]triphosphate (GTP gamma S). Levels of Ca2+ that pertain in unstimulated neutrophils (100 nM) are obligatory for the full expression of enzyme activity stimulated with GTP gamma S. Reduction of Ca2+ to 1 nM leads to inhibition. Increasing the level of Ca2+ from 100 nM to 1000 nM does not alter enzyme activity. Guanosine 5'-[beta-thio]diphosphate (GDP beta S) does not stimulate the phosphodiesterase but is an effective inhibitor of activation by GTP gamma S. Ca2+ in the millimolar range can also activate the phosphodiesterase alone and this is not inhibited by GDP beta S. It is also shown that Sr2+ in the millimolar range can stimulate enzyme activity similarly to Ca2+.
mesh_terms: D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000201:enzymology; D004533:Egtazic Acid; D004789:Enzyme Activation / Q000187:drug effects; D006150:Guanine Nucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D009504:Neutrophils / Q000201:enzymology*; D054801:Phosphoinositide Phospholipase C; D010727:Phosphoric Diester Hydrolases / Q000097:blood*; D013324:Strontium / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology
chemical_list: D006150:Guanine Nucleotides; D013873:Thionucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004533:Egtazic Acid; D006160:Guanosine Triphosphate; D010727:Phosphoric Diester Hydrolases; D054801:Phosphoinositide Phospholipase C; D002118:Calcium; D013324:Strontium