Glutaredoxins Rapidly Reduce Glutathione Hydroper- and Polysulfides

Hydropersulfides have gained attention as excellent biochemical nucleophiles and membrane-protective radical scavengers. They form perthiyl radicals, which terminate radical chain reactions through self-recombination, yielding polysulfides. It is currently unknown exactly how polysulfides are subsequently reduced. Using stopped-flow kinetic measurements in combination with mass spectrometry, we show that the model class I glutaredoxin from Plasmodium falciparum (PfGrx) rapidly reduces the polysulfides glutathione trisulfide (GS₃G) and tetrasulfide (GS₄G), yielding glutathionylated PfGrx and the corresponding glutathione hydropersulfide (GSSH) and hydrotrisulfide (GS₃H). The second-order rate constants of these reductions ≥10⁷ M^-1s^-1 are even slightly higher than for glutathione disulfide (GSSG). In contrast, PfGrx was inactive or only moderately active toward cystine or cysteine trisulfide. GSSH and GS₃H are further reduced by PfGrx with second-order rate constants on the order of 10^6-10⁷ M^-1s^-1, yielding glutathionylated PfGrx and hydrogen sulfide (H₂S) or hydrogen disulfide (H₂S₂), respectively. Thus, glutaredoxins specifically recognize the glutathione moiety of glutathione (hydro)per/polysulfides. Since reduced glutathione (GSH) rapidly reduces glutathionylated glutaredoxins, glutathione (hydro)per/polysulfides are efficiently converted to GSSG and H₂S or the corresponding hydrogen polysulfides. As a consequence, the steady-state concentration of glutathione (hydro)per/polysulfides should be tightly controlled in subcellular compartments containing active glutaredoxins and high GSH concentrations.