The Quantitative Significance of the Transsulfuration Enzymes for H 2 S Production in Murine Tissues (original) (raw)
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Biogenesis of Hydrogen Sulfide and Thioethers by Cystathionine Beta-Synthase
Antioxidants & Redox Signaling
Aims: The transsulfuration pathway enzymes cystathionine beta-synthase (CBS) and cystathionine gammalyase are thought to be the major source of hydrogen sulfide (H 2 S). In this study, we assessed the role of CBS in H 2 S biogenesis. Results: We show that despite discouraging enzyme kinetics of alternative H 2 S-producing reactions utilizing cysteine compared with the canonical condensation of serine and homocysteine, our simulations of substrate competitions at biologically relevant conditions suggest that cysteine is able to partially compete with serine on CBS, thus leading to generation of appreciable amounts of H 2 S. The leading H 2 S-producing reaction is condensation of cysteine with homocysteine, while cysteine desulfuration plays a dominant role when cysteine is more abundant than serine and homocysteine is limited. We found that the serine-to-cysteine ratio is the main determinant of CBS H 2 S productivity. Abundance of cysteine over serine, for example, in plasma, allowed for up to 43% of CBS activity being responsible for H 2 S production, while excess of serine typical for intracellular levels effectively limited such activity to less than 1.5%. CBS also produced lanthionine from serine and cysteine and a third of lanthionine coming from condensation of two cysteines contributed to the H 2 S pool. Innovation: Our study characterizes the H 2 S-producing potential of CBS under biologically relevant conditions and highlights the serine-to-cysteine ratio as the main determinant of H 2 S production by CBS in vivo. Conclusion: Our data clarify the function of CBS in H 2 S biogenesis and the role of thioethers as surrogate H 2 S markers. Antioxid. Redox Signal. 28, 311-323.
Enzymology of H 2 S Biogenesis, Decay and Signaling
Antioxidants & Redox Signaling, 2014
Significance: Hydrogen sulfide (H 2 S), produced by the desulfuration of cysteine or homocysteine, functions as a signaling molecule in an array of physiological processes including regulation of vascular tone, the cellular stress response, apoptosis, and inflammation. Recent Advances: The low steady-state levels of H 2 S in mammalian cells have been recently shown to reflect a balance between its synthesis and its clearance. The subversion of enzymes in the cytoplasmic trans-sulfuration pathway for producing H 2 S from cysteine and/or homocysteine versus producing cysteine from homocysteine, presents an interesting regulatory problem. Critical Issues: It is not known under what conditions the enzymes operate in the canonical trans-sulfuration pathway and how their specificity is switched to catalyze the alternative H 2 S-producing reactions. Similarly, it is not known if and whether the mitochondrial enzymes, which oxidize sulfide and persulfide (or sulfane sulfur), are regulated to increase or decrease H 2 S or sulfane-sulfur pools. Future Directions: In this review, we focus on the enzymology of H 2 S homeostasis and discuss H 2 S-based signaling via persulfidation and thionitrous acid. Antioxid. Redox Signal. 20, 770-782.
Involvement of redox-signalling in endogenous hydrogen sulfide production
British Journal of Pharmacology, 2012
Recently, cystathionine-g-lyase (CSE) was found to provide the major physiological pathway for H2S, the third member of the gasotransmitter family. In various pathophysiological conditions, H2S exerted protective effects based on its antioxidant, anti-inflammatory, anti-hypertensive and other regulatory functions. Interestingly, CSE expression had been only poorly studied and only in relation with inflammatory processes. Therefore, the study by Hassan et al. in this issue of the BJP, provides a considerable advance by furnishing direct experimental evidence for the involvement of redox signalling in the regulation of CSE gene expression. They found that PDGF up-regulated CSE expression and activity that was abolished by antioxidants and by deletion of the transcription factor nuclear erythroid-2-related factor-2 (Nrf2). Furthermore, PDGF induced Nrf2 binding to its consensus sequence that was again reversed by antioxidants. As Nrf2 also governs CO biosynthesis, and PDGF inversely affects H2S and NO production, these data could indicate a concerted regulation of the three gasotransmitters by redox signalling.
2016
Long noncoding RNAs (lncRNAs) are emerging as main nodes of regulatory networks underlying developmental processes in Eukaryotes. Their action is particularly relevant in the central nervous system, whose wide variety of cells are highly transcriptionally active and express almost half of the lncRNAs detected in the human brain [1]. In addition, their potential activity as oncosuppressors or oncogenes and their association with cancer subtypes and clinical prognosis is also emerging [2].
Hydrogen sulfide chemical biology: Pathophysiological roles and detection
Nitric Oxide, 2013
Hydrogen sulfide (H 2 S) is the most recent endogenous gasotransmitter that has been reported to serve many physiological and pathological functions in different tissues. Studies over the past decade have revealed that H 2 S can be synthesized through numerous pathways and its bioavailability regulated through its conversion into different biochemical forms. H 2 S exerts its biological effects in various manners including redox regulation of protein and small molecular weight thiols, polysulfides, thiosulfate/ sulfite, iron-sulfur cluster proteins, and anti-oxidant properties that affect multiple cellular and molecular responses. However, precise measurement of H 2 S bioavailability and its associated biochemical and pathophysiological roles remains less well understood. In this review, we discuss recent understanding of H 2 S chemical biology, its relationship to tissue pathophysiological responses and possible therapeutic uses.
PLOS ONE, 2015
Urothelium, the epithelial lining the inner surface of human bladder, plays a key role in bladder physiology and pathology. It responds to chemical, mechanical and thermal stimuli by releasing several factors and mediators. Recently it has been shown that hydrogen sulfide contributes to human bladder homeostasis. Hydrogen sulfide is mainly produced in human bladder by the action of cystathionine-β-synthase. Here, we demonstrate that human cystathionine-β-synthase activity is regulated in a cGMP/PKG-dependent manner through phosphorylation at serine 227. Incubation of human urothelium or T24 cell line with 8-Bromo-cyclic-guanosine monophosphate (8-Br-cGMP) but not dibutyryl-cyclic-adenosine monophosphate (d-cAMP) causes an increase in hydrogen sulfide production. This result is congruous with the finding that PKG is robustly expressed but PKA only weakly present in human urothelium as well as in T24 cells. The cGMP/PKG-dependent phosphorylation elicited by 8-Br-cGMP is selectively reverted by KT5823, a specific PKG inhibitor. Moreover, the silencing of cystathionine-β-synthase in T24 cells leads to a marked decrease in hydrogen sulfide production either in basal condition or following 8-Br-cGMP challenge. In order to identify the phosphorylation site, recombinant mutant proteins of cystathionine-β-synthase in which Ser32, Ser227 or Ser525 was mutated in Ala were generated. The Ser227Ala mutant cystathionine-β-synthase shows a notable reduction in basal biosynthesis of hydrogen sulfide becoming unresponsive to the 8-Br-cGMP challenge. A specific antibody that recognizes the phosphorylated form of cystathionine-β-synthase has been produced and validated by using T24 cells and human urothelium. In conclusion, human cystathionine-β-synthase can be phosphorylated in a PKG-dependent manner at Ser227 leading to an increased catalytic activity.
Biochemistry, 2011
Cystathionine β-synthase (CBS) catalyzes the first step in the transsulfuration pathway in mammals, i.e., the condensation of serine and homocysteine to produce cystathionine and water. Recently, we have reported a steady-state kinetic analysis of the three hydrogen sulfide (H 2 S)generating reactions that are catalyzed by human and yeast CBS (Singh et al (2009) J Biol Chem 284: 22457-66). In the current study, we report a pre-steady-state kinetic analysis of intermediates in the H 2 S-generating reactions catalyzed by yeast CBS (yCBS). Because yCBS does not have a heme cofactor, in contrast to human CBS, it is easier to observe reaction intermediates with yCBS. The most efficient route for H 2 S generation by yCBS is the β-replacement of the cysteine thiol by homocysteine. In this reaction, yCBS first reacts with cysteine to release H 2 S and forms an aminoacrylate intermediate (k obs =1.61 ± 0.04 mM −1 s −1 at low cysteine and 2.8 ± 0.1 mM −1 s −1 at high cysteine concentrations, at 20 °C), which has an absorption maximum at 465 nm. Homocysteine binds to the E•aminoacrylate intermediate with a bimolecular rate constant of 142 mM −1 s −1 and rapidly condenses to form the enzyme-bound external aldimine of cystathionine. The reactions could be partially rate limited by release of the products, cystathionine and H 2 S. Hydrogen sulfide (H 2 S)1, like nitric oxide and carbon monoxide, is a gaseous signaling molecule (1-3) that elicits a variety of physiological effects. In the cardiovascular system, H 2 S apparently functions as a vasorelaxant (4) and as a cardioprotective agent (5). A dosedependent decrease in murine blood pressure by sodium hydrosulfide has been reported (4). Other reported effects of H 2 S include protection against ischemia reperfusion injury and anti-inflammatory effects in tissues (5,6). In lower organisms like yeast, H 2 S plays a role in population synchronization during ultradian oscillations (7). There are two known mammalian enzymes that can directly generate H 2 S: cystathionase γ-lyase (CGL) and CBS (8). A third enzyme pair, 3-mercaptopyruvate sulfurtransferase together with cysteine aminotransferase, catalyzes the transfer of sulfur to an unknown acceptor and, in the presence of a reductant, can liberate H 2 S (3,9). The role of CGL-dependent H 2 S production in the vasculature is controversial with one group reporting development of age-related hypertension in CGL knockout mice (4) and another, a normotensive phenotype (10).
H2S and its role in redox signaling
Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics, 2014
Hydrogen sulfide (H 2 S) has emerged as an important gaseous signaling molecule that is produced endogenously by enzymes in the sulfur metabolic network. H 2 S exerts its effects on multiple physiological processes important under both normal and pathological conditions. These functions include neuromodulation, regulation of blood pressure and cardiac function, inflammation, cellular energetics and apoptosis. Despite the recognition of its biological importance and its beneficial effects, the mechanism of H 2 S action and the regulation of its tissue levels remain unclear in part owing to its chemical and physical properties that render handling and analysis challenging. Furthermore, the multitude of potential H 2 S effects has made it difficult to dissect its signaling mechanism and to identify specific targets. In this review, we focus on H 2 S metabolism and provide an overview of the recent literature that sheds some light on its mechanism of action in cellular redox signaling in health and disease. This article is part of a Special Issue entitled: Thiol-Based Redox Processes.
American Journal of Physiology-Heart and Circulatory Physiology, 2010
Homocysteine, a cardiovascular and neurocognitive disease risk factor, is converted to hydrogen sulfide, a cardiovascular and neuronal protectant, through the transsulfuration pathway. Given the damaging effects of free homocysteine in the blood and the importance of blood homocysteine concentration as a prognosticator of disease, we tested the hypotheses that the blood itself regulates homocysteine-hydrogen sulfide metabolism through transsulfuration and that transsulfuration capacity and hydrogen sulfide availability protect the endothelium from redox stress. Here we show that the transsulfuration enzymes, cystathionine β-synthase and cystathionine γ-lyase, are secreted by microvascular endothelial cells and hepatocytes, circulate as members of the plasma proteome, and actively produce hydrogen sulfide from homocysteine in human blood. We further demonstrate that extracellular transsulfuration regulates cell function when the endothelium is challenged with homocysteine and that hy...