PubMed · 10848051
(1) A possible cause of asymptomatic "hyperchloraemia" or hyperchloraemia associated with neurological disorders. (2) Bromide-based preparations must not be prescribed or dispensed.
Explore connections, maps & timelines
1998. Bromide intoxication.. https://pubmed.ncbi.nlm.nih.gov/10848051/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Eosinophil peroxidase has been implicated in promoting oxidative tissue damage in a variety of inflammatory conditions, including asthma. It uses H(2)O(2) to oxidize chloride, bromide and thiocyanate to their respective hypohalous acids. The aim of this study was to establish which oxidants eosinophil peroxidase produces under physiological conditions. By measuring rates of H(2)O(2) utilization by the enzyme at neutral pH, we determined the catalytic rate constants for bromide and thiocyanate as 248 and 223 s(-1) and the Michaelis constants as 0.5 and 0.15 mM respectively. On the basis of these values thiocyanate is preferred 2.8-fold over bromide as a substrate for eosinophil peroxidase. Eosinophil peroxidase catalysed substantive oxidation of chloride only below pH 6.5. We found that when eosinophil peroxidase or myeloperoxidase oxidized thiocyanate, another product besides hypothiocyanite was formed; it also converted methionine into methionine sulphoxide. During the oxidation of thiocyanate, the peroxidases were present as their compound II forms. Compound II did not form when GSH was included to scavenge hypothiocyanite. We propose that the unidentified oxidant was derived from a radical species produced by the one-electron oxidation of hypothiocyanite. We conclude that at plasma concentrations of bromide (20-120 microM) and thiocyanate (20-100 microM), hypobromous acid and oxidation products of thiocyanate are produced by eosinophil peroxidase. Hypochlorous acid is likely to be produced only when substrates preferred over chloride are depleted. Thiocyanate should be considered to augment peroxidase-mediated toxicity because these enzymes can convert relatively benign hypothiocyanite into a stronger oxidant.
Whether reductive dehalogenation proceeds via a one- or a two-electron mechanism has been suggested to affect product distributions, hence potentially influencing the success of engineered treatment systems. In this work, we explore vicinal dibromide stereoisomers as "probes" of the concertedness of electron transfer in reduction by aqueous suspensions of iron and zinc metal. Dibromides consisted of 2,3-dibromopentane (diBP) stereoisomers and (+/-)-1,2-dibromo-1,2-diphenylethane. All dibromides reacted with metals to give the same E:Z ratio of olefins observed during dehalogenation by iodide (a two-electron reductant). Reduction by Cr(II) (a one-electron reductant) yielded distinctly different proportions of E and Z olefins. Although this might be construed as evidence that metals function as two-electron reductants, high stereo-specificity was also obtained for reduction of diBPs by Fe(II) adsorbed to goethite, a presumed one-electron reductant; this can be explained by two single-electron transfers in rapid succession, facilitated by the locally elevated concentration of reducing equivalents at the oxide-water interface. The results suggest that reduction of alkyl halides by metals is not likely to produce free radicals that persist long enough to undergo radical-radical coupling or hydrogen-atom abstraction from minor dissolved constituents. Apparent free-radical coupling products are more likely to result from (possibly surface-bound) organometallic intermediates.
The structure of the conjugative coupling protein TrwBDeltaN70 from Escherichia coli plasmid R388 was solved using two crystal forms. This large multimeric membrane protein of 437 residues per monomer is involved in cell-to-cell single-strand DNA transfer. Diffraction data to 2.4 A were available from trigonal crystals obtained from ammonium sulfate and to 2.5 A from monoclinic crystals grown from tartrate. A single tantalum bromide (Ta(6)Br(12)(2+)) derivative of the trigonal form, which presented a protein hexamer with C6 local symmetry in the asymmetric unit, was used in a three-wavelength MAD experiment to achieve 4.5 A resolution for initial phases. Sixfold averaging and phase extension increased the effective phasing resolution and eventually produced a straightforwardly traceable electron-density map. The monoclinic structure was solved by molecular replacement, i.e. a hexamer of the trigonal form was used as a search model. Two such hexamers are present in the asymmetric unit.