Selective Irreversible Inhibition of Neuronal and Inducible Nitric-oxide Synthase in the Combined Presence of Hydrogen Sulfide and Nitric Oxide.
J Biol Chem
; 290(41): 24932-44, 2015 Oct 09.
Article
em En
| MEDLINE
| ID: mdl-26296888
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 â¼2.4·10(-5) and â¼7.9·10(-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 â¼1.5·10(-5) m at pH 6.0 and increased to â¼8.3·10(-5) m at pH 8.0. Preincubation of concentrated nNOS with H2S under turnover conditions decreased activity after dilution by â¼70%, 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 â¼1.9·10(-5) m in the presence of Arg and BH4 but exhibited much higher IC50 values (â¼1.0-6.1·10(-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 â¼ 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.
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Base de dados:
MEDLINE
Assunto principal:
Inibidores Enzimáticos
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Óxido Nítrico Sintase Tipo I
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Óxido Nítrico Sintase Tipo II
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Sulfeto de Hidrogênio
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Óxido Nítrico
Limite:
Animals
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Humans
Idioma:
En
Revista:
J Biol Chem
Ano de publicação:
2015
Tipo de documento:
Article