title: Light activation of phospholipase A2 in rod outer segments of bovine retina and its modulation by GTP-binding proteins.
abstract: Light stimulates phospholipase A2 activity in rod outer segments (ROS) of bovine retina as measured by the liberation of arachidonate from phosphatidylcholine, in in vitro assays of dark-adapted ROS. A role for GTP-binding proteins (G or N proteins) in the light activation of phospholipase A2 is suggested by the capacity for guanosine 5'-O-(thiotriphosphate) (GTP gamma S) to activate phospholipase A2 in dark-adapted ROS. In contrast, addition of GTP gamma S coincident with light exposure inhibited the light activation of phospholipase A2, suggesting that phospholipase A2 activity in the ROS is under dual regulation by G proteins. Transducin, the major G protein of the ROS, mediates the activation of cGMP phosphodiesterase by light and is a substrate for both cholera and pertussis toxin. Treatment of dark-adapted ROS with either toxin inhibits both basal and light-activated phospholipase A2, mimicking the action of the toxins on the light-induced cGMP phosphodiesterase activity of ROS. There is a loss of light-sensitive phospholipase A2 activity coincident with extraction of transducin from ROS membranes. In addition, the light-sensitive phospholipase A2 activity can be partially restored by the addition of purified transducin to the extracted ROS membranes. Light activation of phospholipase A2 in ROS membranes thus occurs by a transducin-dependent mechanism.
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D002417:Cattle; D002772:Cholera Toxin / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects / Q000528:radiation effects; D019204:GTP-Binding Proteins / Q000502:physiology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D008027:Light; D008565:Membrane Proteins / Q000502:physiology; D037342:Pertussis Toxin; D010713:Phosphatidylcholines / Q000378:metabolism; D010740:Phospholipases / Q000528:radiation effects*; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000528:radiation effects*; D054467:Phospholipases A2; D010786:Photoreceptor Cells / Q000201:enzymology*; D012374:Rod Cell Outer Segment / Q000201:enzymology*; D013873:Thionucleotides / Q000494:pharmacology; D015293:Transducin; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D001095:Arachidonic Acids; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D016718:Arachidonic Acid; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D002772:Cholera Toxin; D037342:Pertussis Toxin; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D019204:GTP-Binding Proteins; D015293:Transducin