Cytochrome c Reduction by H₂S Potentiates Sulfide Signaling

Abstract

Hydrogen sulfide (HS) is an endogenously produced gas that is toxic at high concentrations. It is eliminated by a dedicated mitochondrial sulfide oxidation pathway, which connects to the electron transfer chain at the level of complex III. Direct reduction of cytochrome c (Cyt C) by HS has been reported previously but not characterized. In this study, we demonstrate that reduction of ferric Cyt C by HS exhibits hysteretic behavior, which suggests the involvement of reactive sulfur species in the reduction process and is consistent with a reaction stoichiometry of 1.5 mol of Cyt C reduced/mol of HS oxidized. HS increases O consumption by human cells (HT29 and HepG2) treated with the complex III inhibitor antimycin A, which is consistent with the entry of sulfide-derived electrons at the level of complex IV. Cyt C-dependent HS oxidation stimulated protein persulfidation in vitro, while silencing of Cyt C expression decreased mitochondrial protein persulfidation in a cell culture. Cyt C released during apoptosis was correlated with persulfidation of procaspase 9 and with loss of its activity. These results reveal a potential role for the electron transfer chain in general, and Cyt C in particular, for potentiating sulfide-based signaling.

Hydrogen sulfide perturbs mitochondrial bioenergetics and triggers metabolic reprogramming in colon cells

“…The sulfide oxidation pathway generates reactive sulfur species that could be important in signaling (18,19). We therefore used the fluorescent SSP4 probe (20) to examine whether SQR activity modulates sulfane sulfur levels.…”

H2S and reactive sulfur signaling at the host-bacterial pathogen interface

“…Emerging evidence in mammalian systems demonstrates the role of ferric (Fe III )-heme in the oxidation of H 2 S, which reduces the Fe III to Fe II and forms the one-electron oxidized radical HS • upon dissociation ( Fig. 4A) (117)(118)(119)(120)(121). Recent work reveals that this mechanism is used to reactivate enzymes requiring a catalytically active ferrous heme from the inactive ferric state, formed during turnover (121).…”

The Role of Host-Generated H2S in Microbial Pathogenesis: New Perspectives on Tuberculosis

“…The mechanism of this inhibition is complex, involving as many as three sulfide molecules, acting both as an electron donor and a ligand to oxidized states of C c O, including ferric heme a 3 ( Cooper and Brown, 2008 ). Sulfide also reduces cytochrome c , providing electrons for C c O, and the sulfur oxidation product(s) increases protein persulfidation, thereby possibly potentiating sulfide signaling ( Vitvitsky et al., 2018 ). A similar formation of sulfur oxidation products from endogenously produced sulfide has been reported for intact red blood cells, mediated by hemoglobin ( Vitvitsky et al., 2015 ).…”