PubMed · 14172892
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O TADA. 1964. [NITRIC OXIDE].. https://pubmed.ncbi.nlm.nih.gov/14172892/
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We identified the RNA-binding protein Rop, encoded on the pOSAK1 plasmid of enterohaemorrhagic Escherichia coli (EHEC), as a novel factor that enhances nitric oxide (NO) resistance, although it has previously been reported to regulate plasmid copy number. The Rop-induced increase in NO resistance was significantly reduced in several small noncoding RNA (sRNA) gene-deficient EHEC mutants. Among these sRNAs, DsrA, ArcZ, and RprA were directly involved in the translational regulation of rpoS expression, suggesting that Rop modulates rpoS expression through sRNAs. To examine this mechanism, we generated sRNA gene-deficient mutants with an additional deletion of the 5' untranslated region (5' UTR) of rpoS, which is required for translational regulation. The increase in NO resistance by Rop was restored in the double mutant, suggesting that this phenotype is mediated by Rop-dependent interactions between sRNAs and the 5' UTR of rpoS mRNA. Furthermore, Rop promoted rpoS mRNA degradation, an effect that likely suppresses RpoS production and may thereby enhance NO resistance. Finally, an hfq-deficient EHEC mutant exhibited no increase in NO resistance in the presence of Rop, indicating that Hfq is essential for Rop-mediated NO resistance.
Oxidative modifications of amino acids in proteins can serve to regulate enzyme activity. This emerging field of redox regulation is related to other cellular signaling pathways, however, neither the chemical mechanisms in the cellular environment nor the affected metabolic and physiological changes are well understood. From data on endotoxin action in vascular tissue and reports on thiol modifications and tyrosine nitrations a unified scheme with five key components is proposed, governed solely by variations in the fluxes of nitrogen monoxide (NO) and superoxide (O(2)(-)). Crucial to the interactions is the formation of peroxynitrite which at concentrations of 10(-9)-10(-6)M elicits events like activation of prostanoid formation, metal catalyzed nitrations and two electron oxidations at cysteines and methionines. As a new concept we postulate that peroxynitrite formed in situ from NO and O(2)(-) is in rapid equilibrium with excess NO to form a nitrosating species that transfers NO(+). The resulting S-nitrosations occur prior to oxidative peroxynitrite action and seem to be involved in the down-regulation of reductive pathways. As the flux of O(2)(-) exceeds the one of NO, cellular damage develops induced by one-electron oxidations caused by nitrogen dioxide and by the Fenton reaction.
Two distinct stages, which can be monitored spectrophotometrically, have been observed for the first time in multiple reactions between thiol, such as l-cysteine and some well-known nitrovasodilators, namely S-nitroso-N-acetyl-d,l-penicillamine (SNAP), S-nitrosoglutathione (GSNO), and S-nitrosocaptopril (SNOCap) in aqueous solution (in the presence of EDTA). The first part of the reaction occurs at stopped-flow time scale ( approximately 10(-2)s(-1)) in one single step and has been found to be transnitrosation; followed by a slow decomposition of the products of the transnitrosation reaction with the formation of a variety of nitrogen products. Reactivity with regard to the first stage occurs in the order GSNO>SNAP>SNOCap. The second stage shows first-order rate constants of the order 10(-4)s(-1), although some degree of complexity exists in elucidating an accurate rate equation with which a comparative study could be done.