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Hydrogen sulfate5/25/2023 ![]() H 2S is generated subsequently by the β-elimination reaction of cysteine catalyzed by either CBS or CSE. CSE catalyzes the α,γ-elimination of cystathionine to cysteine, α-ketobutyrate and NH 3. The β-replacement reaction of homocysteine with serine is catalyzed by the CBS and generates cystathionine. CBS and CSE are a part of the reverse transsulfuration pathway. H 2S is generated in the tissues by cysteine metabolizing enzymes, cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST) in conjunction with cysteine aminotransferase (CAT). In addition, erythrocytes are able to convert elemental sulfur to HS - by non-enzymatic reduction. Sulfate-reducing bacteria (SRB) colonize the gut and in the presence of an electron donor reduce sulfate to produce H 2S. H 2S is produced in mammalian organisms by non-enzymatic and enzymatic pathways. In order to develop H 2S-releasing donors, researchers started to modify chemical structures of well-described sulfide releasing agents, obtaining several H 2S donors including Lawesson’s reagent and analogues, DTT (1,2-dithiole-3-thiones) derivatives like ADT-OH, ACS 5, ACS 48 and ACS 50, diallyl disulfide (DADS) derivatives like ACS 81, arylthioamides (TBZ), aryl isothiocyanates and thiourea derivatives ( Figure 1). Therefore, H 2S is now regarded as a third gaseous signaling molecule, next to nitric oxide (NO) and carbon monoxide (CO). These effects are believed to be mediated by physiological concentrations of H 2S. Later, a number of important biological actions of H 2S were described, including vasorelaxation, changes in brain neurotransmission, and the effect on neuronal K + channel activity. The 1996 report from Abe and Kimura, suggesting the role of endogenously produced H 2S in neuromodulation, started a new era in H 2S research, and its role in biology and medicine. Similarly, the toxic effects of H 2S on mammals have been known over the centuries. ![]() ![]() First reports linking H 2S with the smell of rotten eggs can be traced back in the 18th century (reviewed in ). Hydrogen sulfide (H 2S) is produced by a variety of organisms, e.g., bacteria, fungi, plants and animals.
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