Coenzyme Q and Related Quinones Oxidize HS to Polysulfides and Thiosulfate

In the canonical pathway for mitochondrial HS oxidation electrons are transferred from sulfide:quinone oxidoreductase (SQR) to complex III via ubiquinone (CoQ). We previously observed that a number of quinones directly oxidize HS and we hypothesize that CoQ may have similar properties. Here we examine HS oxidation by CoQ and more hydrophilic, truncated forms, CoQ and CoQ, in buffer using HS and polysulfide fluorophores (AzMC and SSP4), silver nanoparticles to measure thiosulfate (HSO), mass spectrometry to identify polysulfides and O-sensitive optodes to measure O consumption. We show that all three quinones concentration-dependently catalyze the oxidization of HS to polysulfides and thiosulfate in buffer with the potency CoQ>CoQ>CoQ and that CoQ specifically oxidizes HS to per-polysulfides, HS. These reactions consume and require oxygen and are augmented by addition of SOD suggesting that the quinones, not superoxide, oxidize HS. Related quinones, MitoQ, menadione and idebenone, oxidize HS in similar reactions. Exogenous CoQ decreases cellular HS and increases polysulfides and thiosulfate production and this is also O-dependent, suggesting that the quinone has similar effects on sulfur metabolism in cells. Collectively, these results suggest an additional endogenous mechanism for HS metabolism and a potential therapeutic approach in HS-related metabolic disorders.