title: Catalytic consumption of nitric oxide by prostaglandin H synthase-1 regulates platelet function.
abstract: Nitric oxide (( small middle dot)NO) plays a central role in vascular homeostasis via regulation of smooth muscle relaxation and platelet aggregation. Although mechanisms for ( small middle dot)NO formation are well known, removal pathways are less well characterized, particularly in cells that respond to ( small middle dot)NO through activation of soluble guanylate cyclase. Herein, we report that ( small middle dot)NO is catalytically consumed by prostaglandin H synthase-1 (PGHS-1) through acting as a reducing peroxidase substrate. With purified ovine PGHS-1, ( small middle dot)NO consumption requires peroxide (LOOH or H(2)O(2)), with a K(m)( (app)) for 15(S)hydroperoxyeicosatetraenoic acid (HPETE) of 3. 27 +/- 0.35 microm. During this, 2 mol ( small middle dot)NO are consumed per mol HPETE, and loss of HPETE hydroperoxy group occurs with retention of the conjugated diene spectrum. Hydroperoxide-stimulated ( small middle dot)NO consumption requires heme incorporation, is not inhibited by indomethacin, and is further stimulated by the reducing peroxidase substrate, phenol. PGHS-1-dependent ( small middle dot)NO consumption also occurs during arachidonate, thrombin, or activation of platelets (1-2 microm.min(-1) for typical plasma platelet concentrations) and prevents ( small middle dot)NO stimulation of platelet soluble guanylate cyclase. Platelet sensitivity to ( small middle dot)NO as an inhibitor of aggregation is greater using a platelet-activating stimulus () that does not cause ( small middle dot)NO consumption, indicating that this mechanism overcomes the anti-aggregatory effects of ( small middle dot)NO. Catalytic consumption of ( small middle dot)NO during eicosanoid synthesis thus represents both a novel proaggregatory function for PGHS-1 and a regulated mechanism for vascular ( small middle dot)NO removal.
authors.affiliation: Wales Heart Research Institute, University of Wales College of Medicine, Heath Park, Cardiff CF4 4XN, United Kingdom. odonnellvb@cardiff.ac.uk
authors.forename: V B
authors.initials: VB
authors.lastname: O'Donnell
authors.forename: B
authors.initials: B
authors.lastname: Coles
authors.forename: M J
authors.initials: MJ
authors.lastname: Lewis
authors.forename: B C
authors.initials: BC
authors.lastname: Crews
authors.forename: L J
authors.initials: LJ
authors.lastname: Marnett
authors.forename: B A
authors.initials: BA
authors.lastname: Freeman
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology; D001792:Blood Platelets / Q000502:physiology*; D002384:Catalysis; D002417:Cattle; D051545:Cyclooxygenase 1; D005978:Glutathione / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D015289:Leukotrienes / Q000378:metabolism; D008054:Lipid Peroxides / Q000378:metabolism; D008565:Membrane Proteins; D009569:Nitric Oxide / Q000378:metabolism*; D009603:Nitroso Compounds / Q000494:pharmacology; D010974:Platelet Aggregation / Q000502:physiology*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D026422:S-Nitrosoglutathione; D012756:Sheep; D013379:Substrate Specificity; D013917:Thrombin / Q000494:pharmacology
chemical_list: D007527:Isoenzymes; D015289:Leukotrienes; D008054:Lipid Peroxides; D008565:Membrane Proteins; D009603:Nitroso Compounds; D010975:Platelet Aggregation Inhibitors; D016718:Arachidonic Acid; D009569:Nitric Oxide; D026422:S-Nitrosoglutathione; C025086:15-hydroperoxy-5,8,11,13-eicosatetraenoic acid; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D006861:Hydrogen Peroxide; D051545:Cyclooxygenase 1; C496511:PTGS1 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; D013917:Thrombin; D005978:Glutathione