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Abstract
The modification of protein and non-protein thiols by oxidants including hydrogen
peroxide (H(2)O(2)), peroxynitrite anion (ONOO(-)) and hypochlorous acid (HOCl) is
well documented. Using an aromatic thiol, 5-thio-2-nitrobenzoic acid, and biologically
relevant oxidants, we have identified higher oxidation states of sulfur including
the sulfonic acid derivative and the disulfide S-oxide, a thiosulfinate, by HPLC and
mass spectrometry. The initial reaction of ONOO(-) with 5-thio-2-nitrobenzoic acid
yielded a transient red intermediate, the sulfenate anion. The red intermediate was
observed when ONOO(-) and H(2)O(2) were used to oxidize 5-thio-2-nitrobenzoic acid
and it persisted for several seconds at pH 7. HOCl oxidized the disulfide, 5,5'dithiobis(2-nitrobenzoic
acid) to the corresponding sulfonic acid and no additional products were detected.
Using this system, we can directly compare the thiol-oxidizing abilities of several
oxidants. Because 5-thio-2-nitrobenzoic acid is the product of the reaction of Ellman's
reagent with protein thiols, a detailed study of its stability in biological matrices
where oxidants may be generated is warranted.