Mechanism and regulation of peroxidase-catalyzed nitric oxide consumption in physiological fluids: critical protective actions of ascorbate and thiocyanate.
Free Radic Biol Med
; 72: 91-103, 2014 Jul.
Article
em En
| MEDLINE
| ID: mdl-24704973
ABSTRACT
Catalytic consumption of nitric oxide (NO) by myeloperoxidase and related peroxidases is implicated as playing a key role in impairing NO bioavailability during inflammatory conditions. However, there are major gaps in our understanding of how peroxidases consume NO in physiological fluids, in which multiple reactive enzyme substrates and antioxidants are present. Notably, ascorbate has been proposed to enhance myeloperoxidase-catalyzed NO consumption by forming NO-consuming substrate radicals. However, we show that in complex biological fluids ascorbate instead plays a critical role in inhibiting NO consumption by myeloperoxidase and related peroxidases (lactoperoxidase, horseradish peroxidase) by acting as a competitive substrate for protein-bound redox intermediates and by efficiently scavenging peroxidase-derived radicals (e.g., urate radicals), yielding ascorbyl radicals that fail to consume NO. These data identify a novel mechanistic basis for how ascorbate preserves NO bioavailability during inflammation. We show that NO consumption by myeloperoxidase Compound I is significant in substrate-rich fluids and is resistant to competitive inhibition by ascorbate. However, thiocyanate effectively inhibits this process and yields hypothiocyanite at the expense of NO consumption. Hypothiocyanite can in turn form NO-consuming radicals, but thiols (albumin, glutathione) readily prevent this. Conversely, where ascorbate is absent, glutathione enhances NO consumption by urate radicals via pathways that yield S-nitrosoglutathione. Theoretical kinetic analyses provide detailed insights into the mechanisms by which ascorbate and thiocyanate exert their protective actions. We conclude that the local depletion of ascorbate and thiocyanate in inflammatory microenvironments (e.g., due to increased metabolism or dysregulated transport) will impair NO bioavailability by exacerbating peroxidase-catalyzed NO consumption.
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Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Ácido Ascórbico
/
Tiocianatos
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Peroxidase
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Biocatálise
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Óxido Nítrico
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Antioxidantes
Limite:
Animals
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Humans
Idioma:
En
Revista:
Free Radic Biol Med
Assunto da revista:
BIOQUIMICA
/
MEDICINA
Ano de publicação:
2014
Tipo de documento:
Article