Thiosulfate Formation Research Articles

A new sulfur bioconversion process development for energy- and space-efficient secondary wastewater treatment

Harvesting organic matter from wastewater, chemical enhanced primary treatment for instance, is widely applied to maximize energy recovery; however, it limits the applicability of secondary treatment for acceptable effluent discharge into surface water bodies. To turn this bottleneck issue into an opportunity, this study developed oxygen-induced thiosulfatE production duRing sulfATe reduction (ERATO) to provide efficient electron donor for denitrification or partial denitrification anammox in wastewater treatment. Typical pretreated wastewater was synthesized with chemical oxygen demand of 110 mg/L, sulfate of 50 mg S/L, ammonium of 30 mgN/L, and varying dissolved oxygen (DO) and was fed into a moving-bed biofilm reactor (MBBR) with a short hydraulic retention time of 40 min. The ORP maintained at − 311 mV in the bioreactor, indicating that the influent DO was vanished immediately when it enters the bioreactor. In 349 days’ continuous operation, the surface-specific sulfate reduction rate reached 0.42 g S/(m2·d). Notably, the formation rate of thiosulfate reached 0.12–0.18 g S/(m2·d) with a high thiosulfate-Sproduced/sulfide-Sproduced ratio of 38–73% when influent DO was 2.7–3.6 mg/L, much higher than 0–17% obtained in previously reported sulfate-reducing process. Then, batch tests and metabolism analysis were conducted to confirm the oxygen effect on thiosulfate formation, and to explore the mechanism of oxygen-induced thiosulfate formation in ERATO. Results examined that oxygen supply promoted the thiosulfate-Sproduced/sulfide-Sproduced ratio from 4% to 24–26%, demonstrated that S0 and sulfate were critical for thiosulfate production, and indicated that oxygen induces thiosulfate formation mainly through: sulfide first oxidized to S0 which then reacts with sulfite derived from oxygen-regulated biological sulfate reduction (S0 + SO32−→S2O32−). The proposed compact ERATO process with high thiosulfate production, supporting space- and energy-efficient secondary wastewater treatment.

Novel Adsorption-Catalysis Design of CuO Impregnated CeO2 Nanorods As Cathode Modifier for Lithium-Sulfur Battery

Lithium sulfur batteries (LSBs) are a promising candidate to be used in modern commodities like electric vehicles, grid energy storage, electric aviation, and many others because of the exceptionally high theoretical capacity of sulfur (1675 mAh g-1), almost 5 times higher than the conventional lithium-ion batteries. However, the problem of polysulfide shuttling effect originating from the dissolved lithium polysulfides in the electrolyte results in poor cycling stability, hindering the commercialization of LSB. Significant advancement has been made over the years due to a great deal of research on novel materials development and structural design for lithium polysulfide (Li2Sn: 4≤ n ≤8) adsorption synergy to counter the polysulfide shuttling effect 1. However, rather than focusing only on the adsorption synergy (Physical confinement and chemical binding), novel catalysts that can accelerate the polysulfide conversion reaction kinetics are needed to design the next generation LSB. Previously, our group investigated shape-controlled cerium oxide (CeO2) to accelerate the polysulfide conversion reactions by generating the intermediate steps of thiosulfate and polythionate 2, 3. Copper oxide (CuO), being a p-type semiconducting material, is another promising material that can activate thiosulfate formation as its redox potential is 2.53 V vs Li/Li+, which lies in the potential window of 2.4 V < E° ≤ 3.05 V that selectively triggers the formation of thiosulfate. Herein, we investigated 10 wt% of CuO impregnated on the CeO2 nanorods (10 wt%CuO/CeO2) as a cathode host for LSB. The CuO impregnation on the surface of CeO2 nanorods attributed strong interaction between the surface defect rich CeO2 nanorods and the copper oxides (CuOx: Cu2O and CuO) promoting excellent electrocatalytic activity. The 10 wt%CuO/CeO2 sample provides adsorption-catalysis dual synergy to chemically bind and further catalyze the polysulfide conversion by polythionate and thiosulfate generation. As a result, the derived LSB exhibited excellent electrochemical performance with high capacity of 1141 mAh g-1 at 0.2 C with a sulfur loading of 1.33 mg cm-2 and a capacity loss of only 0.04% per cycle after 60 cycles. Key words: lithium sulfur batteries, lithium polysulfides, shuttle effect, cerium oxide, catalysis. Xiong, D. G.; Zhang, Z.; Huang, X. Y.; Huang, Y.; Yu, J.; Cai, J. X.; Yang, Z. Y., Boosting the polysulfide confinement in B/N–codoped hierarchically porous carbon nanosheets via Lewis acid–base interaction for stable Li–S batteries. Journal of Energy Chemistry 2020, 51, 90-100. Azam, S.; Wei, Z.; Wang, R., Cerium oxide nanorods anchored on carbon nanofibers derived from cellulose paper as effective interlayer for lithium sulfur battery. J Colloid Interface Sci 2022, 615, 417-431. Wei, Z.; Li, J.; Wang, R., Surface engineered polar CeO2-based cathode host materials for immobilizing lithium polysulfides in High-performance Li-S batteries. Applied Surface Science 2022, 580.

Investigating role of abiotic side and finding optimum abiotic condition for improving gas biodesulfurization using Thioalkalivibrio versutus

Hydrogen sulfide (H2S) is a super toxic substance that produces SOx gases when combusted. Therefore, it should be removed from gas streams. Biodesulfurization is one of the developing methods for removing sulfide. Gas biodesulfurization must be accelerated to be competitive with chemical processes. This process has two sides: biotic and abiotic sides. To increase the rate of sulfide removal, this substance should be given to the bacteria in the maximum amount (Max. − RHS B). Therefore, it is necessary to minimize the rate of adverse abiotic reactions of sulfide (Min. − RHS A). Minimizing the sulfide reaction with biosulfur and oxygen and thiosulfate generation (Min. − RHS thio2) was assessed in de-microbized medium. It was concluded that the pH should be kept as low as possible. The kinetics of thiosulfate formation from sulfide oxidation (− RHS thio1) are strongly dependent on the sulfide concentration, and to minimize this reaction rate, sulfide should be gently injected into the culture. To minimize sulfide reduction to hydrogen sulfide (Min. − RHS rev), the pH should be kept as high as possible. Using the Design Expert v.13, a model was driven for the abiotic side to obtain optimum condition. The pH value was found to be 8.2 and the sulfide concentration to 2.5E−05 M. Thioalkalivibrio versutus cultivation under identified abiotic conditions resulted in biological removal of sulfide up to 1.5 g/h. The culture was not able to remove 2 g/h input sulfide, and to increase this, the biotic side should be studied.

Comparison of sulfide-oxidizing Sulfurimonas strains reveals a new mode of thiosulfate formation in subsurface environments.

Sulfur-oxidizing Sulfurimonas spp. are widespread in sediments, hydrothermal vent fields, aquifers and subsurface environments such as oil reservoirs where they play an important role in the sulfur cycle. We determined the genome sequence of the oil field isolate Sulfurimonas sp. strain CVO and compared its gene expression during nitrate-dependent sulfide oxidation to the coastal sediment isolate Sulfurimonas denitrificans. Formation of elemental sulfur (S0 ) and high expression of sulfide quinone oxidoreductase (SQR) genes indicates that sulfide oxidation in both strains is mediated by SQR. Subsequent oxidation of S0 was achieved by the sulfur oxidation enzyme complex (SOX). In the coastal S. denitrificans, the genes are arranged and expressed as two clusters: soxXY1 Z1 AB and soxCDY2 Z2 H, and sulfate was the sole metabolic end product. By contrast, the oil field strain CVO has only the soxCDY2 Z2 H cluster and not soxXY1 Z1 AB. Despite the absence of the soxXY1 Z1 AB cluster, strain CVO oxidized S0 to thiosulfate and sulfate, demonstrating that soxCDY2 Z2 H genes alone are sufficient for S0 oxidation in Sulfurimonas spp. and that thiosulfate is an additional metabolic end product. Screening of publicly available metagenomes revealed that Sulfurimonas spp. with only the soxCDY2 Z2 H cluster are widespread suggesting this mechanism of thiosulfate formation is environmentally significant.

The Role of Hemoproteins: Hemoglobin, Myoglobin and Neuroglobin in Endogenous Thiosulfate Production Processes.

Thiosulfate formation and biodegradation processes link aerobic and anaerobic metabolism of cysteine. In these reactions, sulfite formed from thiosulfate is oxidized to sulfate while hydrogen sulfide is transformed into thiosulfate. These processes occurring mostly in mitochondria are described as a canonical hydrogen sulfide oxidation pathway. In this review, we discuss the current state of knowledge on the interactions between hydrogen sulfide and hemoglobin, myoglobin and neuroglobin and postulate that thiosulfate is a metabolically important product of this processes. Hydrogen sulfide oxidation by ferric hemoglobin, myoglobin and neuroglobin has been defined as a non-canonical hydrogen sulfide oxidation pathway. Until recently, it appeared that the goal of thiosulfate production was to delay irreversible oxidation of hydrogen sulfide to sulfate excreted in urine; while thiosulfate itself was only an intermediate, transient metabolite on the hydrogen sulfide oxidation pathway. In the light of data presented in this paper, it seems that thiosulfate is a molecule that plays a prominent role in the human body. Thus, we hope that all these findings will encourage further studies on the role of hemoproteins in the formation of this undoubtedly fascinating molecule and on the mechanisms responsible for its biological activity in the human body.

Characterization of a newly isolated strain Pseudomonas sp. C27 for sulfide oxidation: Reaction kinetics and stoichiometry.

Sulfide biooxidation by the novel sulfide-oxidizing bacteria Pseudomonas sp. C27, which could perform autotrophic and heterotrophic denitrification in mixotrophic medium, was studied in batch and continuous systems. Pseudomonas sp. C27 was able to oxidize sulfide at concentrations as high as 17.66 mM. Sulfide biooxidation occurred in two distinct stages, one resulting in the formation of sulfur with nitrate reduction to nitrite, followed by thiosulfate formation with nitrite reduction to N2. The composition of end-products was greatly impacted by the ratio of sulfide to nitrate initial concentrations. At a ratio of 0.23, thiosulfate represented 100% of the reaction products, while only 30% with a ratio of 1.17. In the continuous bioreactor, complete removal of sulfide was observed at sulfide concentration as high as 9.38 mM. Overall sulfide removal efficiency decreased continuously upon further increases in influent sulfide concentrations. Based on the experimental data kinetic parameter values were determined. The value of maximum specific growth rate, half saturation constant, decay coefficient, maintenance coefficient and yield were to be 0.11 h−1, 0.68 mM sulfide, 0.11 h−1, 0.21 mg sulfide/mg biomass h and 0.43 mg biomass/mg sulfide, respectively, which were close to or comparable with those reported in literature by other researches.

Transient Kinetic Analysis of Hydrogen Sulfide Oxidation Catalyzed by Human Sulfide Quinone Oxidoreductase

The first step in the mitochondrial sulfide oxidation pathway is catalyzed by sulfide quinone oxidoreductase (SQR), which belongs to the family of flavoprotein disulfide oxidoreductases. During the catalytic cycle, the flavin cofactor is intermittently reduced by sulfide and oxidized by ubiquinone, linking H2S oxidation to the electron transfer chain and to energy metabolism. Human SQR can use multiple thiophilic acceptors, including sulfide, sulfite, and glutathione, to form as products, hydrodisulfide, thiosulfate, and glutathione persulfide, respectively. In this study, we have used transient kinetics to examine the mechanism of the flavin reductive half-reaction and have determined the redox potential of the bound flavin to be -123 ± 7 mV. We observe formation of an unusually intense charge-transfer (CT) complex when the enzyme is exposed to sulfide and unexpectedly, when it is exposed to sulfite. In the canonical reaction, sulfide serves as the sulfur donor and sulfite serves as the acceptor, forming thiosulfate. We show that thiosulfate is also formed when sulfide is added to the sulfite-induced CT intermediate, representing a new mechanism for thiosulfate formation. The CT complex is formed at a kinetically competent rate by reaction with sulfide but not with sulfite. Our study indicates that sulfide addition to the active site disulfide is preferred under normal turnover conditions. However, under pathological conditions when sulfite concentrations are high, sulfite could compete with sulfide for addition to the active site disulfide, leading to attenuation of SQR activity and to an alternate route for thiosulfate formation.

The role of compartment-specific cysteine synthesis for sulfur homeostasis during H2S exposure in Arabidopsis.

Sulfide is the end-product of assimilatory sulfate reduction in chloroplasts. It is then used by O-acetylserine(thiol)lyase (OAS-TL) to produce cysteine, the source of reduced sulfur in plants. While its formation in chloroplasts is essential for plant metabolism, sulfide is also a potent toxin mainly targeting respiration in mitochondria. Here, the application of sublethal concentrations of sulfide to Arabidopsis thaliana was used to by-pass assimilatory sulfate reduction, resulting in down-regulation of most genes of the pathway. The dualism of sulfide as substrate and toxin was investigated using knock-out mutants of the chloroplast-, mitochondrion- and cytosol-targeted OAS-TL isoforms. Surprisingly, growth retardation due to intoxication by sulfide was independent of the presence or absence of the three OAS-TL isoforms, indicating rapid exchange towards sulfur homoeostasis between the compartments. Cysteine, glutathione and sulfate, and less so S-sulfocysteine, were identified as major sinks for excess sulfide in wild-type plants. Additionally, the concentration of thiosulfate increased 1,000-fold, pointing towards a significant function of thiosulfate formation during H2S exposure. Synthesis of cysteine in the cytosol was found to be particularly important for accumulation of sulfite, sulfate and thiosulfate, indicating an important role for cytosolic OAS-TL for the re-oxidation of sulfide. The results show that thiosulfate and sulfate accumulation is strongly linked to cytosolic cysteine synthesis and that scavenging of sulfide by cysteine synthesis enhances sulfur compound accumulation. However, lack of cysteine synthesis in a subcellular compartment has no crucial consequences for toxicity and subsequent growth retardation.

Multiple sulfur isotopes fractionations associated with abiotic sulfur transformations in Yellowstone National Park geothermal springs.

BackgroundThe paper presents a quantification of main (hydrogen sulfide and sulfate), as well as of intermediate sulfur species (zero-valent sulfur (ZVS), thiosulfate, sulfite, thiocyanate) in the Yellowstone National Park (YNP) hydrothermal springs and pools. We combined these measurements with the measurements of quadruple sulfur isotope composition of sulfate, hydrogen sulfide and zero-valent sulfur. The main goal of this research is to understand multiple sulfur isotope fractionation in the system, which is dominated by complex, mostly abiotic, sulfur cycling.ResultsWater samples from six springs and pools in the Yellowstone National Park were characterized by pH, chloride to sulfate ratios, sulfide and intermediate sulfur species concentrations. Concentrations of sulfate in pools indicate either oxidation of sulfide by mixing of deep parent water with shallow oxic water, or surface oxidation of sulfide with atmospheric oxygen. Thiosulfate concentrations are low (<6 μmol L-1) in the pools with low pH due to fast disproportionation of thiosulfate. In the pools with higher pH, the concentration of thiosulfate varies, depending on different geochemical pathways of thiosulfate formation. The δ34S values of sulfate in four systems were close to those calculated using a mixing line of the model based on dilution and boiling of a deep hot parent water body. In two pools δ34S values of sulfate varied significantly from the values calculated from this model. Sulfur isotope fractionation between ZVS and hydrogen sulfide was close to zero at pH < 4. At higher pH zero-valent sulfur is slightly heavier than hydrogen sulfide due to equilibration in the rhombic sulfur–polysulfide – hydrogen sulfide system. Triple sulfur isotope (32S, 33S, 34S) fractionation patterns in waters of hydrothermal pools are more consistent with redox processes involving intermediate sulfur species than with bacterial sulfate reduction. Small but resolved differences in ∆33S among species and between pools are observed.ConclusionsThe variation of sulfate isotopic composition, the origin of differences in isotopic composition of sulfide and zero–valent sulfur, as well as differences in ∆33S of sulfide and sulfate are likely due to a complex network of abiotic redox reactions, including disproportionation pathways.

New Method for H2S Removal in Acid Solutions

Several different technologies are available for H(2)S removal from the gas stream of medium capacity. Among them, the most widely used is Locat with more than 120 plants worldwide. In the last decade, many new processes, such as Sulfatreat-DO, Crystasulf, Caltech, and UCSR, were proposed to overcome the drawbacks of the state-of-the-art processes (low sulfur purity, chemical degradation, thiosulfate formation). We have developed a new H(2)S conversion method based on acid ferric nitrate solution, co-catalyzed by a heteropolyacid. H(2)S was converted to pure sulfur (>99.9 %), with no traces of organic compounds. Due to the acid pH of the solution, no chelant or surfactant was needed and iron content in the solution could reach very high levels. Keggin heteropolyacid (H(6)PW(9)V(3)O(40)) catalyzed the reoxidation of reduced ferrous solution with air at mild temperature and at very high reaction rate. The undesired side reaction (NO(x) formation) could be avoided by simply increasing the oxygen partial pressure.

Biological Treatment of Toxic Petroleum Spent Caustic in Fluidized Bed Bioreactor Using Immobilized Cells of Thiobacillus RAI01

In the present studies, newly isolated Thiobacillus sp was used for the treatment of synthetic spent sulfide caustic in a laboratory-scale fluidized bed bioreactor. The sulfide oxidation was tested using Ca-alginate immobilized Thiobacillus sp. Initially, response surface methodology was applied for the optimization of four parameters to check the sulfide oxidation efficiency in batch mode. Further, reactor was operated in continuous mode for 51 days at different sulfide loading rates and retention times to test the sulfide oxidation and sulfate and thiosulfate formation. Sulfide conversions in the range of 90-98% were obtained at almost all sulfide loading rates and hydraulic retention times. However, increased loading rates resulted in lower sulfide oxidation capacity. All the experiments were conducted at constant pH of around 6 and temperature of 30 +/- 5 degrees C.

The Effect of pH on Thiosulfate Formation in a Biotechnological Process for the Removal of Hydrogen Sulfide from Gas Streams

In a biotechnological process for hydrogen sulfide (H2S) removal from gas streams, operating at natronophilic conditions, formation of thiosulfate (S2O3(2-)) is unfavorable, as it leads to a reduced sulfur production. Thiosulfate formation was studied in gas-lift bioreactors, using natronophilic biomass at [Na+] + [K+] = 2 mol L(-1). The results show that at sulfur producing conditions, selectivity for S2O3(2-) formation mainly depends on the equilibrium between free sulfide (HS(-)) and polysulfide (Sx(2-)), which can be controlled via the pH. At pH 8.6, 21% of the total dissolved sulfide is present as Sx(2-) and selectivity for S2O3(2-) formation is 3.9-5.5%. At pH 10, 87% of the total dissolved sulfide is present as Sx(2-) and 20-22% of the supplied H2S is converted to S2O3(2-), independent of the H2S loading rate. Based on results of bioreactor experiments and biomass activity tests, a mechanistic model is proposed to describe the relation between S2O3(2-) formation and pH.

Kinetics of sulfur isotope exchange between aqueous sulfide and thiosulfate involving intra- and intermolecular reactions at hydrothermal conditions

Sulfur isotope exchange between sulfide (H 2S) and thiosulfate (HSSO 3H) can be described by the general rate law for a two-compound system (X and AB) with three exchangeable atoms (X, A, and B) proposed by [X. Chu, H. Ohmoto, Kinetics of isotope exchange reactions involving intra- and intermolecular reactions: I. Rate law for a system with two chemical compounds and three exchangeable atoms. Geochim. Cosmochim. Acta 55 1991 1953–1961]. According to the rate law, the isotope exchange reaction is comprised of one overall intramolecular exchange between sulfane (–SH or SH) and sulfonate (–SO 3H or SO 3H) sulfurs of thiosulfate (i.e., SH⇔SO 3H in thiosulfate) and two overall intermolecular exchanges between sulfide and sulfane sulfur of thiosulfate (i.e., H 2S⇔SH of thiosulfate) and between sulfide and sulfonate sulfur of thiosulfate (i.e., H 2S⇔SO 3H of thiosulfate). The rate constants for the three overall exchange reactions and the equilibrium isotopic fractionation factors among sulfide, sulfane, and sulfonate of thiosulfate were estimated by fitting [F. Uyama, H. Chiba, M. Kusakabe, H. Sakai, Sulfur isotope exchange reaction in the aqueous system: thiosulfate–sulfide–sulfate at hydrothermal temperature. Geochem. J. 19 1985 301–315] experimental data on sulfur isotope exchange between aqueous H 2S and sodium thiosulfate by the least squares method. At temperatures of 100–170 °C, the equilibrium fractionation factors (in per mil) can be expressed as: 1000 ⁢ ln α H 2 S – SH = − 0.327 ± 0.055 ( 10 12 / T 4 ) + 2.676 ± 0.341 ( 10 6 / T 2 ) 1000 ⁢ ln α SO 3 H – SH = − 0.352 ± 0.009 ( 10 12 / T 4 ) + 7.523 ± 0.054 ( 10 6 / T 2 ) and 1000 ⁢ ln α SO 3 H – H 2 S = − 0.0293 ± 0.058 ( 10 12 / T 4 ) − 4.871 ± 0.357 ( 10 6 / T 2 ) ( T in K). At near-neutral pH, the overall rate (m −1 s −1) for the sulfur isotope exchange between H 2S and –SO 3H of thiosulfate is described by log k SO 3 H ⇔ H 2 S = − 5.14 ( 10 3 / T ) + 10.35 ( T in K) with an activation energy of 98.3 kJ/mol at 100–170 °C. A comparison of the rates of sulfur exchanges among H 2S, –SH, and –SO 3H of thiosulfate with the rates of polysulfide–thiosulfate formation and disproportion reactions determined by [W.F. Giggenbach, Kinetics of the polysulfide–thiosulfate disproportionation up to 240 °C. Inorg. Chem. 13 1974b 1730–1733] suggests that the sulfur isotope exchanges between aqueous sulfide and thiosulfate may proceed via the formation and disproportionation of polysulfides (e.g., S 3S 2−, S 4S 2−, etc.): 10H 2S+3S 2O 3 2−=4S 3S 2−+2H ++9H 2O and S n S 2−+SSO 3 2−=S n+1 S 2−+SO 3 2− . The disproportionation reaction of polysulfides appears to control the exchange rate between S 2− and S 6+ atoms in thiosulfate and is considered the rate-determining step in the sulfate–sulfide exchange reaction rather than the intramolecular exchange of thiosulfate proposed by [H. Ohmoto, A.C. Lasaga, Kinetics of reactions between aqueous sulfates and sulfides in hydrothermal systems. Geochim. Cosmochim. Acta 46 1982 1727–1745]. Therefore, polysulfides may play an important role in the chemical and isotopic reactions between aqueous sulfide and sulfate under hydrothermal conditions.

高濃度ポリサルファイドの開発

A new electrolytic oxidation process to produce highly concentrated polysulfide (PS) liquor front the white liquor (WL) has been developed. A specially-designed electrolytic cell makes the system suitable for actual mill operation. The WL, is oxidized to produce PS liquor in the anode compartment. while pure sodium hydroxide is formed in the cathode compartment simultaneously. Since the undesirable thiosulfate formation is easy to control in the electrochemical process, it was possible to produce highly concentrated PS liquor with a good current efficiency. Consequently this process achieves to concentrate sodium sulfide in WL, and produce highly concentrated PS simultaneously, while the sulfur balance in the Kraft pulping process can be maintained. PS with SAQR pulping of hardwoods was evaluated using the oxidized liquor produced by the bench scale cell with the laboratory digester. Then, the large increases of pulp yields and large reductions of kappa number were observed, and modified cooking intensified these effects. A capable case of system closure for the bleached kraft pulp production was also proposed.

Hepatocyte-Catalysed Detoxification of Cyanide by l- and d-Cysteine

The hepatocyte metabolic pathways involved in the detoxification of cyanide by cysteine have been investigated in vitro using hepatocytes isolated from Sprague–Dawley rats. Cyanide toxicity towards isolated hepatocytes could be prevented by the addition of l- or d-cysteine, cystine, or the cysteine metabolites thiosulfate and mercaptopyruvate, which markedly increased thiocyanate formation. Prior depletion of hepatocyte GSH markedly increased thiosulfate formation from l- or d-cysteine without affecting thiocyanate formation from l- or d-cysteine. This suggested that the major metabolic pathway for thiocyanate formation did not involve thiosulfate. Mercaptopyruvate was a more likely metabolic intermediate, as thiocyanate formation from l-cysteine but not thiosulfate was inhibited markedly by aminooxyacetate, a cysteine aminotransferase inhibitor, and propargylglycine, a γ-cystathionase inhibitor. Furthermore, propargylglycine prevented l-cysteine cytoprotection against cyanide toxicity. Thiocyanate formation from d-cysteine likely also involved mercaptopyruvate, as thiocyanate formation from d-cysteine but not l-cysteine was inhibited by benzoate, an inhibitor of d-amino acid oxidase. Furthermore, benzoate prevented d-cysteine cytoprotection against cyanide toxicity. Cystine may also be an intermediate, as hepatocyte thiocyanate formation from added l-cysteine was inhibited when l-cysteine autoxidation was prevented with the copper chelator bathocuproine disulfonate. Furthermore, thiocyanate formation by rat liver homogenates with l-cystine was far more rapid than that with l-cysteine. Hepatocyte thiocyanate metabolic intermediates of β-mercaptopyruvate and thiocystine were proposed for l-cysteine, and β-mercaptopyruvate was proposed for d-cysteine.

The glutathione dependence of inorganic sulfate formation from l- or d-cysteine in isolated rat hepatocytes

The GSH dependence of the metabolic pathways involved in the conversion of cysteine to sulfate in intact cells has been investigated. It was found that hepatocyte-catalysed sulfate formation from added l-cysteine did not occur if hepatocyte GSH was depleted beforehand, but was restored when GSH levels recovered. Furthermore, sulfate formation did not recover in GSH-depleted hepatocytes if GSH synthesis was prevented with buthionine sulfoximine. Thiosulfate formation was, however, markedly enhanced in GSH-depleted hepatocytes. These results suggest that thiosulfate is an intermediate in the formation of inorganic sulfate from l-cysteine and that GSH was required for the conversion of thiosulfate to inorganic sulfate. Much less sulfate was formed if the cysteine was replaced with cysteinesulfinate. Furthermore, sulfate formation from l-cysteine was markedly inhibited by the addition of the transaminase inhibitor dl-cycloserine or the γ-cystathionase inhibitor dl-propargylglycine. The major routes of sulfate formation from l-cysteine therefore seems to involve pathways that do not involve l-cysteinesulfinate. Similar amounts of sulfate were formed from d-cysteine as l-cysteine. Thiosulfate instead of sulfate was also formed in GSH-depleted hepatocytes. However, sulfate formation from d-cysteine differed from l-cysteine in that it was inhibited by the d-aminoacid oxidase inhibitor sodium benzoate and was not affected by transaminase or γ-cystathionase inhibitors. These results suggest that thiosulfate is an intermediate in sulfate formation from d-cysteine and involves the oxidation of d-cysteine by d-amino acid oxidase to form β-mercaptopyruvate.

The Decomposition of Aqueous Dithionite and its reactions with polythionates SnO2−6 (n = 3–5) studied by ion‐pair chromatography

AbstractAqueous dithionite decomposes at 20°C and pH values not far from 7.0 to give thiosulfate and sulfite from which trithionate may form. Addition of thiosulfate accelerates this reaction only at pH &lt; 6. The pH dependence is explained by formation of HS2O3− ions which are reduced by dithionite to HS− and SO2−3. Sulfide destroys dithionite by nucleophilic cleavage, probably with formation of sulfoxylate and thiosulfite ions. The polythionates SnO2−6 (n = 3–5) are reduced by dithionite at pH = 7.0 and 20°C according to SnO2−6 + S2O2−4 + 2 H2O→S2O32− + Sn–3SO32− + 4H1 + 2SO32− The reaction rate rapidly increases with the number n of sulfur atoms. In secondary reactions sulfite attacks SnO62− ions with thiosulfate formation.

Sulfide oxidation under oxygen limitation by a thiobacillus thioparus isolated from a marine microbial mat

The colorless sulfur bacterium Thiobacillus thioparus T5, isolated from a marine microbial mat, was grown in continuous culture under conditions ranging from sulfide limitation to oxygen limitation. Under sulfide-limiting conditions, sulfide was virtually completely oxidized to sulfate. Under oxygen-limiting conditions, sulfide was partially oxidized to zerovalent sulfur (75%) and thiosulfate (17%). In addition, low concentrations of tetrathionate and polysulfide were detected. The finding of in vivo thiosulfate formation supports the discredited observations of thiosulfate formation in cell free extracts in the early sixties. In a microbial mat most sulfide oxidation was shown to take place under oxygen-limiting conditions. It is suggested that zerovalent sulfur formation by thiobacilli is a major process resulting in polysulfide accumulation. Implications for the competition between colorless sulfur bacteria and purple sulfur bacteria are discussed.

Inhibition of sulfate-forming activity in rat liver mitochondria by (aminooxy)acetate

The effect of (aminooxy)acetate, an inhibitor of aminotransferases, on the sulfate formation fromL-cysteine andL-cysteinesulfinate in rat liver mitochondria was studied. Incubation of 10 mML-cysteine with rat liver mitochondria at 37°C in the presence of 10 mM 2-oxoglutarate and 10 mM glutathione resulted in the formation of 4.60 and 1.52µmol of sulfate and thiosulfate, respectively, per 60 min per mitochondria obtained from 1 g of liver. Under the same conditions sulfate formation fromL-cysteinesulfinate was 24.96µmol, but thiosulfate was not formed. The addition of (aminooxy)acetate at 2 mM or more completely inhibited the sulfate and thiosulfate formation fromL-cysteine and the sulfate formation fromL-cysteinesulfinate. These findings support our previous conclusion that cysteine transamination and 3-mercaptopyruvate pathway (MP pathway) are involved in the sulfate formation fromL-cysteine in rat liver mitochondria (Ubuka et al., 1992).

L-Cysteine metabolism via 3-mercaptopyruvate pathway and sulfate formation in rat liver mitochondria

We have studied the 3-mercaptopyruvate pathway (transamination pathway) ofL-cysteine metabolism in rat liver mitochondria.L-Cysteine and other substrates at 10 mM concentration were incubated with mitochondrial fraction at pH 8.4, and sulfate and thiosulfate were determined by ion chromatography. WhenL-cysteine alone was incubated, sulfate formed was 0.7µmol per mitochondria from one g of liver per 60 min. Addition of 2-oxoglutarate and GSH resulted in more than 3-fold increase in sulfate formation, and thiosulfate was formed besides sulfate. The sum (A + 2B) of sulfate (A) and thiosulfate (B) formed was approximately 7-times that withL-cysteine alone. Incubation with 3-mercaptopyruvate resulted in sulfate and thiosulfate formation, and sulfate was formed with thiosulfate. These reactions were stimulated with glutathione. Sulfate formation fromL-cysteinesulfinate and 2-oxoglutarate was not enhanced by glutathione and thiosulfate was not formed. These findings indicate thatL-cysteine was metabolized and sulfate was formed through 3-mercaptopyruvate pathway in mitochondria.