Ozone Oxidizes Glutathione to a Sulfonic Acid

Abstract

Biosurfaces are universally covered with fluid microfilms containing reduced glutathione (GSH) and other antioxidants whose putative roles include the detoxification of ambient ozone (O_3). It is generally believed that O_3 accepts an electron from the thiolate GS^(2-) function [pK_a(GS^-) = 8.8] of GSH to produce thiyl GS^(•-) radicals en route to the disulfide GSSG. Here, we report novel electrospray mass spectrometry experiments showing that sulfonates (GSO_3^-/GSO_3^(2-)), not GSSG, are the exclusive final products on the surface of aqueous GSH microdroplets exposed to dilute O_3(g) for ~1 ms. The higher reactivity of the thiolate GS^(2-) toward O_3(g) over the thiol GS^- is kinetically resolved in this time frame due to slow GS^- acid dissociation. However, our experiments also show that O_3 will be largely scavenged by the more reactive ascorbate coantioxidant in typical interfacial biofilms. The presence of GSSG and the absence of GSO_3^-/GSO_3^(2-) in extracellular lining fluids are therefore evidence of GSH oxidation by species other than O_3.

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