title: Selective Irreversible Inhibition of Neuronal and Inducible Nitric-oxide Synthase in the Combined Presence of Hydrogen Sulfide and Nitric Oxide.
abstract: Citrulline formation by both human neuronal nitric-oxide synthase (nNOS) and mouse macrophage inducible NOS was inhibited by the hydrogen sulfide (H2S) donor Na2S with IC50 values of ∼2.4·10(-5) and ∼7.9·10(-5) m, respectively, whereas human endothelial NOS was hardly affected at all. Inhibition of nNOS was not affected by the concentrations of l-arginine (Arg), NADPH, FAD, FMN, tetrahydrobiopterin (BH4), and calmodulin, indicating that H2S does not interfere with substrate or cofactor binding. The IC50 decreased to ∼1.5·10(-5) m at pH 6.0 and increased to ∼8.3·10(-5) m at pH 8.0. Preincubation of concentrated nNOS with H2S under turnover conditions decreased activity after dilution by ∼70%, suggesting irreversible inhibition. However, when calmodulin was omitted during preincubation, activity was not affected, suggesting that irreversible inhibition requires both H2S and NO. Likewise, NADPH oxidation was inhibited with an IC50 of ∼1.9·10(-5) m in the presence of Arg and BH4 but exhibited much higher IC50 values (∼1.0-6.1·10(-4) m) when Arg and/or BH4 was omitted. Moreover, the relatively weak inhibition of nNOS by Na2S in the absence of Arg and/or BH4 was markedly potentiated by the NO donor 1-(hydroxy-NNO-azoxy)-l-proline, disodium salt (IC50 ∼ 1.3-2.0·10(-5) m). These results suggest that nNOS and inducible NOS but not endothelial NOS are irreversibly inhibited by H2S/NO at modest concentrations of H2S in a reaction that may allow feedback inhibition of NO production under conditions of excessive NO/H2S formation.
authors: From the Departments of Pharmacology and Toxicology and.
authors: Christian L
authors: CL
authors: Heine
authors: From the Departments of Pharmacology and Toxicology and.
authors: Renate
authors: R
authors: Schmidt
authors: From the Departments of Pharmacology and Toxicology and.
authors: Kerstin
authors: K
authors: Geckl
authors: From the Departments of Pharmacology and Toxicology and.
authors: Astrid
authors: A
authors: Schrammel
authors: Pharmaceutical Chemistry, Institute of Pharmaceutical Sciences, Karl Franzens University Graz, A-8010 Graz, Austria.
authors: Bernd
authors: B
authors: Gesslbauer
authors: From the Departments of Pharmacology and Toxicology and.
authors: Kurt
authors: K
authors: Schmidt
authors: From the Departments of Pharmacology and Toxicology and.
authors: Bernd
authors: B
authors: Mayer
authors: From the Departments of Pharmacology and Toxicology and antonius.gorren@uni-graz.at.
authors: Antonius C F
authors: AC
authors: Gorren
mesh_terms: D000818:Animals; D002956:Citrulline / Q000096:biosynthesis; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004926:Escherichia coli / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005978:Glutathione / Q000494:pharmacology; D006801:Humans; D006862:Hydrogen Sulfide / Q000494:pharmacology*; D051379:Mice; D009249:NADP / Q000378:metabolism; D009569:Nitric Oxide / Q000494:pharmacology*; D052248:Nitric Oxide Synthase Type I / Q000037:antagonists & inhibitors* / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors* / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D013438:Sulfhydryl Compounds / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D013438:Sulfhydryl Compounds; D002956:Citrulline; D009569:Nitric Oxide; D009249:NADP; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D005978:Glutathione; D006862:Hydrogen Sulfide
keywords: enzyme inactivation; hydrogen sulfide; nitric oxide; nitric-oxide synthase; reactive nitrogen species (RNS)