Jon M. Fukuto's research while affiliated with Sonoma State University and other places

1,4-naphthoquinones (NQs) catalytically oxidize H2S to per- and polysufides and sulfoxides, reduce oxygen to superoxide and hydrogen peroxide, and can form NQ-SH adducts through Michael addition. Here, we measured oxygen consumption and used sulfur-specific fluorophores, liquid chromatography tandem mass spectrometry (LC-MS/MS), and UV-Vis spectrometry to examine H2S oxidation by NQs with various substituent groups. In general, the order of H2S oxidization was DCNQ ~ juglone > 1,4-NQ > plumbagin >DMNQ ~ 2-MNQ > menadione, although this order varied somewhat depending on the experimental conditions. DMNQ does not form adducts with GSH or cysteine (Cys), yet it readily oxidizes H2S to polysulfides and sulfoxides. This suggests that H2S oxidation occurs at the carbonyl moiety and not at the quinoid 2 or 3 carbons, although the latter cannot be ruled out. We found little evidence from oxygen consumption studies or LC-MS/MS that NQs directly oxidize H2S2–4, and we propose that apparent reactions of NQs with inorganic polysulfides are due to H2S impurities in the polysulfides or an equilibrium between H2S and H2Sn. Collectively, NQ oxidation of H2S forms a variety of products that include hydropersulfides, hydropolysulfides, sulfenylpolysulfides, sulfite, and thiosulfate, and some of these reactions may proceed until an insoluble S8 colloid is formed.

Cysteine-bound sulfane sulfur atoms in proteins have received much attention as key factors in cellular redox homeostasis. However, the role of sulfane sulfur in zinc regulation has been overlooked. We report here that cysteine-bound sulfane sulfur atoms serve as ligands to hold and release zinc ions in growth inhibitory factor (GIF)/metallothionein-3 (MT3) with an unexpected C–S–S–Zn structure. Oxidation of such a zinc/persulfide cluster in Zn7GIF/MT3 results in the release of zinc ions, and intramolecular tetrasulfide bridges in apo-GIF/MT3 efficiently undergo S–S bond cleavage by thioredoxin to regenerate Zn7GIF/MT3. Three-dimensional molecular modeling confirmed the critical role of the persulfide group in the thermostability and Zn-binding affinity of GIF/MT3. The present discovery raises the fascinating possibility that the function of other Zn-binding proteins is controlled by sulfane sulfur.

Cysteine-bound sulfane sulfur atoms in proteins have received much attention as key factors in cellular redox homeostasis. However, the role of sulfane sulfur in zinc regulation has been overlooked. We report here that cysteine-bound sulfane sulfur atoms serve as ligands to hold and release zinc ions in growth inhibitory factor (GIF)/metallothionein-3 (MT3) with an unexpected C–S–S–Zn structure. Oxidation of such a zinc/persulfide cluster in Zn7GIF/MT3 results in the release of zinc ions, and intramolecular tetrasulfide bridges in apo-GIF/MT3 efficiently undergo S–S bond cleavage by thioredoxin to regenerate Zn7GIF/MT3. Three-dimensional molecular modeling confirmed the critical role of the persulfide group in the thermostability and Zn-binding affinity of GIF/MT3. The present discovery raises the fascinating possibility that the function of other Zn-binding proteins is controlled by sulfane sulfur.

Cysteine-bound sulfane sulfur atoms in proteins have received much attention as key factors in cellular redox homeostasis. However, the role of sulfane sulfur in zinc regulation has been overlooked. We report here that cysteine-bound sulfane sulfur atoms serve as ligands to hold and release zinc ions in growth inhibitory factor (GIF)/metallothionein-3 (MT3) with an unexpected C-S-S-Zn structure. Oxidation of such a zinc/persulfide cluster in Zn7GIF/MT3 results in the release of zinc ions, and intramolecular tetrasulfide bridges in apo-GIF/MT3 efficiently undergo S-S bond cleavage by thioredoxin to regenerate Zn7GIF/MT3. Three-dimensional molecular modeling confirmed the critical role of the persulfide group in the thermostability and Zn-binding affinity of GIF/MT3. The present discovery raises the fascinating possibility that the function of other Zn-binding proteins is controlled by sulfane sulfur.

Hydropersulfides (RSSH) are oxidized thiol (RSH) derivatives that have been shown to be biologically prevalent with likely important functions (along with other polysulfur compounds). The functional utility of RSSH can be gleaned from their unique chemical properties. That is, RSSH possess chemical reactivity not present in other biologically relevant sulfur species that should allow them to be used in specific ways in biology as effector/signaling molecules. For example, compared to RSH, RSSH are considered to be superior nucleophiles, reductants and metal ligands. Moreover, unlike RSH, RSSH can be either reductants/nucleophiles or oxidants/electrophiles depending on the protonated state. It has also become clear that studies related to the chemical biology and physiology of hydrogen suflide (H2S) must also consider the effects of RSSH (and related polysulfur species) as they are biochemically linked. Herein is a discussion of the relevant chemistry of RSSH that can serve as a basis for understanding how RSSH can be used by cells to, for example, combat stresses and used in signaling. Also, discussed are some current experimental studies regarding the biological activity of RSSH that can be explained by their chemical properties.

Earlier studies revealed the presence of cysteine persulfide (CysSSH) and related polysulfide species in various mammalian tissues. CysSSH has both antioxidant and oxidant properties, modulates redox-dependent signal transduction and has been shown to mitigate oxidative stress. However, its functional relevance in the setting of myocardial ischaemia/reperfusion injury (IRI) remains unknown. The present study was undertaken to (1) study the dynamics of production and consumption of persulfides under normoxic and hypoxic conditions in the heart, and (2) determine whether exogenous administration of the CysSSH donor, cysteine trisulfide (Cys-SSS-Cys) at the onset of reperfusion rescues functional impairment and myocardial damage by interfering with lipid peroxidation. Utilising a well-established ex vivo Langendorff murine model, we here demonstrate that endogenous tissue concentrations of CysSSH are upregulated when oxygen supply is compromised (global myocardial ischaemia) and rapidly restored to baseline levels upon reperfusion, suggestive of active regulation. In a separate set of experiments, exogenous administration of Cys-SSS-Cys for 10 min at the onset of reperfusion was found to decrease malondialdehyde (MDA) concentrations, formation of 4-hydroxynonenal (4-HNE) protein adducts and rescue the heart from injury. Cys-SSS-Cys also restored post-ischaemic cardiac function, improving both coronary flow and left ventricular developed pressure (LVDP). Taken together, these results support the notion that endogenous CysSSH plays an important role as a “redox preconditioning” agent to combat the oxidative insult in myocardial IRI.

Ferroptosis is a mechanism of cell death that has possible roles in numerous diseases. Two new studies have identified hydropersulfides as potent inhibitors of O2-dependent membrane damage and destruction, and as potential regulators of ferroptosis.

It has become apparent that hydrogen sulfide (H2S), hydropersulfides (RSSH) and other polysulfide species are all intimately linked biochemically. Indeed, at least some of the biological activity attributed to hydrogen sulfide (H2S) may actually be due to its conversion to RSSH and derived polysulfur species (and vice-versa). The unique chemistry associated with the hydropersulfide functional group (-SSH) predicts that it possesses possible protective properties that can help a cell contend with oxidative and/or electrophilic stress. However, since RSSH and polysulfides possess chemical properties akin to disulfides (RSSR), they can also be sources of oxidative/electrophilic stress/signaling as well. Herein are discussed the unique chemistry, possible biochemistry and the physiological implications of RSSH (and polysulfides), especially as it pertains to their putative cellular protection properties against a variety of stresses and/or as possible stressors/signaling agents themselves.

As a member of the group of small di‐ and tri‐atomic endogenous signaling species (i.e. NO, CO, O 2 , and H 2 S), the chemical biology of H 2 S and related and/or derived species has become a topic of significant biological/physiological interest. As the simplest of all biological thiols, much of the biologically relevant chemistry of H 2 S can parallel that of thiols (e.g. cysteine‐based systems). One possible fate of H 2 S in a biological system is the formation of alkylhydropersulfides (RSSH), which possess unique and potentially important biological activity. Indeed, it has been hypothesized that RSSH species represent an important biological functional group that may serve to, among other things, protect cells from oxidative and/or electrophilic stress. Herein, a discussion of the chemical biology of H 2 S and related RSSH species is given as a prelude to begin to try to understand the chemical mechanisms of the possible biological utility of these species.

S-Nitrosothiol (RS-NO) generation/levels have been implicated as being important to numerous physiological and pathophysiological processes. As such, the mechanism(s) of their generation and degradation are important factors in determining their biological activity. Along with the effects on the activity of thiol proteins, RS-NOs have also been reported to be reservoirs or storage forms of nitric oxide (NO). That is, it is hypothesized that NO can be released from RS-NO at opportune times to, for example, regulate vascular tone. However, to date there are few established mechanisms that can account for facile NO release from RS-NO. Recent discovery of the biological formation and prevalence of hydropersulfides (RSSH) and their subsequent reaction with RS-NO species provides a possible route for NO release from RS-NO. Herein, it is found that RSSH is capable of reacting with RS-NO to liberate NO and that the analogous reaction using RSH is not nearly as proficient in generating NO. Moreover, computational results support the prevalence of this reaction over other possible competing processes. Finally, results of biological studies of NO-mediated vasorelaxation are consistent with the idea that RS-NO species can be degraded by RSSH to release NO.