Thiocyanate and chloride as competing substrates for myeloperoxidase

A novel anti-5,5-dimethyl-1-pyrroline N-oxide (DMPO) polyclonal antiserum that specifically recognizes protein radical-derived DMPO nitrone adducts has been developed. In this study, we employed this new approach, which combines the specificity of spin trapping and the sensitivity of antigen-antibody interactions, to investigate protein radical formation from lactoperoxidase (LPO). When LPO reacted with GSH in the presence of DMPO, we detected an LPO radical-derived DMPO nitrone adduct using enzyme-linked immunosorbent assay and Western blotting. The formation of this nitrone adduct depended on the concentrations of GSH, LPO, and DMPO as well as pH values, and GSH could not be replaced by H 2 O 2 . The level of this nitrone adduct was decreased significantly by azide, catalase, ascorbate, iodide, thiocyanate, phenol, or nitrite. However, its formation was unaffected by chemical modification of free cysteine, tyrosine, and tryptophan residues on LPO. ESR spectra showed that a glutathiyl radical was formed from the LPO/GSH/DMPO system, but no protein radical adduct could be detected by ESR. Its formation was decreased by azide, catalase, ascorbate, iodide, or thiocyanate, whereas phenol or nitrite increased it. GSH caused marked changes in the spectrum of compound II of LPO, indicating that GSH binds to the heme of compound II, whereas phenol or nitrite prevented these changes and reduced compound II back to the native enzyme. GSH also dose-dependently inhibited the peroxidase activity of LPO as determined by measuring 2,2 -azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) oxidation. Taken together, these results demonstrate that the GSH-dependent LPO radical formation is mediated by the glutathiyl radical, possibly via the reaction of the glutathiyl radical with the heme of compound II to form a heme-centered radical trapped by DMPO.

Section: Discussionmentioning

confidence: 99%

Protein Radical Formation during Lactoperoxidase-mediated Oxidation of the Suicide Substrate Glutathione

Guo

Detweiler

Mason

2004

“…The purity of EPO preparations was assured before use by demonstrating an RZ of 0.9 (A415/A280), SDS-polyacrylamide gel electrophoresis analysis with Coomassie Blue staining, and in-gel tetramethylbenzidine peroxidase staining to confirm no contaminating myeloperoxidase activity (29). Pentafluorobenzyl hydroxylamine was purchased from Aldrich.…”

Section: Methodsmentioning

confidence: 99%

Eosinophil Peroxidase-derived Reactive Brominating Species Target the Vinyl Ether Bond of Plasmalogens Generating a Novel Chemoattractant, α-Bromo Fatty Aldehyde

Albert¹,

Thukkani²,

Heuertz³

et al. 2003

Plasmalogens are a subclass of glycerophospholipids that are enriched in the plasma membrane of many mammalian cells. The vinyl ether bond of plasmalogens renders them susceptible to oxidation. Accordingly, it was hypothesized that reactive brominating species, a unique oxidant formed at the sites of eosinophil activation, such as in asthma, might selectively target plasmalogens for oxidation. Here we show that reactive brominating species produced by the eosinophil peroxidase system of activated eosinophils attack the vinyl ether bond of plasmalogens. Reactive brominating species produced by eosinophil peroxidase target the vinyl ether bond of plasmalogens resulting in the production of a neutral lipid and lysophosphatidylcholine. Chromatographic and mass spectrometric analyses of this neutral lipid demonstrated that it was 2-bromohexadecanal (2-BrHDA). Reactive brominating species produced by eosinophil peroxidase attacked the plasmalogen vinyl ether bond at acidic pH. Bromide was the preferred substrate for eosinophil peroxidase, and chloride was not appreciably used even at a 1000-fold molar excess. Furthermore, 2-BrHDA production elicited by eosinophil peroxidase-derived reactive brominating species in the presence of 100 M NaBr doubled with the addition of 100 mM NaCl. The potential physiological significance of this pathway was suggested by the demonstration that 2-BrHDA was produced by phorbol myristate acetate-stimulated eosinophils and by the demonstration that 2-BrHDA is a phagocyte chemoattractant. Taken together, the present studies demonstrate the targeting of the vinyl ether bond of plasmalogens by the reactive brominating species produced by eosinophil peroxidase and by activated eosinophils, resulting in the production of brominated fatty aldehydes.

“…Enzyme concentration was determined spectrophotometrically (⑀ 430 ϭ 178 mM Peroxidase Activity Assay-The purity of myeloperoxidase and eosinophil peroxidase were assessed by peroxidase activity using nondenaturing polyacrylamide slab gel electrophoresis and gel system 8 (46,47). Glycerol (25% w/v) and cetyltrimethylammonium bromide (0.05% w/v) were included in all buffers.…”

Section: Methodsmentioning

confidence: 99%

Production of Brominating Intermediates by Myeloperoxidase

Henderson¹,

Byun²,

Williams³

et al. 2001

118

The existence of interhalogen compounds was proposed more than a century ago, but no biological roles have been attributed to these highly oxidizing intermediates. In this study, we determined whether the peroxidases of white blood cells can generate the interhalogen gas bromine chloride (BrCl ؊ -Br ؊ system generated a gas that converted cyclohexene into 1-bromo-2-chlorocyclohexane, implicating BrCl in the reaction. Moreover, human neutrophils used myeloperoxidase, H 2 O 2 , and Br ؊ to brominate deoxycytidine by a taurine-sensitive pathway, suggesting that transhalogenation reactions may be physiologically relevant. 5-Bromouracil incorporated into nuclear DNA is a well known mutagen. Our observations therefore raise the possibility that transhalogenation reactions initiated by phagocytes provide one pathway for mutagenesis and cytotoxicity at sites of inflammation.