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 approximately 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).