The Experts below are selected from a list of 1536 Experts worldwide ranked by ideXlab platform
Michael T. Ashby - One of the best experts on this subject based on the ideXlab platform.
-
Reactive sulfur species: kinetics and mechanisms of the reaction of cysteine Thiosulfinate ester with cysteine to give cysteine sulfenic acid.
Journal of Organic Chemistry, 2007Co-Authors: Péter Nagy, Kelemu Lemma, Michael T. AshbyAbstract:The kinetics and mechanisms of the reaction of cysteine with cysteine Thiosulfinate ester in aqueous solution have been studied by stopped-flow spectrophotometry between pH 6 and 14. Two reaction pathways were observed for pH > 12: (1) an essentially pH-independent nucleophilic attack of cysteinate on cysteine Thiosulfinate ester, and (2) a pH-dependent fast equilibrium protonation of cysteine sulfenate that is followed by rate-limiting comproportionation of cysteine sulfenic acid with cysteinate to give cystine. For 6 < pH < 12, the rate-determining reaction between cysteinate and cysteine Thiosulfinate ester becomes pH-dependent due to the protonation of their amine groups. Hydrolysis of cysteine Thiosulfinate ester does not play a role in the aforementioned mechanisms because the rate-determining nucleophilic attack by hydroxide is relatively slow.
-
Reactive sulfur species: kinetics and mechanisms of the oxidation of cysteine by hypohalous acid to give cysteine sulfenic acid.
Journal of the American Chemical Society, 2007Co-Authors: Péter Nagy, Michael T. AshbyAbstract:Cysteine sulfenic acid has been generated in alkaline aqueous solution by oxidation of cysteine with hypohalous acid (HOX, X = Cl or Br). The kinetics and mechanisms of the oxidation reaction and the subsequent reactions of cysteine sulfenic acid have been studied by stopped-flow spectrophotometry between pH 10 and 14. Two reaction pathways were observed: (1) below pH 12, the condensation of two sulfenic acids to give cysteine Thiosulfinate ester followed by the nucleophilic attack of cysteinate on cysteine Thiosulfinate ester and (2) above pH 10, a pH-dependent fast equilibrium protonation of cysteine sulfenate that is followed by rate-limiting comproportionation of cysteine sulfenic acid with cysteinate to give cystine. The observation of the first reaction suggests that the condensation of cysteine sulfenic acid to give cysteine Thiosulfinate ester can be competitive with the reaction of cysteine sulfenic acid with cysteine.
-
Reactive Sulfur Species: Kinetics and Mechanism of the Hydrolysis of Cysteine Thiosulfinate Ester
Chemical research in toxicology, 2007Co-Authors: Péter Nagy, Michael T. AshbyAbstract:The kinetics and mechanisms of the hydrolysis of cysteine Thiosulfinate ester (CyS(═O)SCyx−, x = 0–2) have been investigated by stopped-flow spectrophotometry between pH 6 and pH 14. The rate-limiting reaction of hydroxide is observed for pH < 13. More complicated kinetics are observed above pH 13, where the hydrolysis of CyS(═O)SCy2− can be fast relative to subsequent reactions. The eventual products of hydrolysis are a 1:1 molar ratio of cystine (CySSCy) and cysteine sufinic acid (CySO2H) under all reaction conditions. The rate of hydrolysis is dependent upon the proton state of CyS(═O)SCyx−. Furthermore, cysteine thiosulfonate ester (CyS(═O)2SCy) was observed as an intermediate during the hydrolysis of CyS(═O)SCyx− at lower pH. CyS(═O)2SCy eventually hydrolyzes to give stoichiometric amounts of CySSCy and CySO2H. However, CySO2H is observed under some conditions for which hydrolysis of CyS(═O)2SCy is relatively slow, thus suggesting multiple hydrolysis pathways for CyS(═O)SCyx−. The mechanism up to the...
Francine Rendu - One of the best experts on this subject based on the ideXlab platform.
-
Allium compounds, dipropyl and dimethyl Thiosulfinates as antiproliferative and differentiating agents of human acute myeloid leukemia cell lines
Dove Medical Press, 2008Co-Authors: Faten Merhi, Jacques Auger, Francine Rendu, Brigitte BauvoisAbstract:Faten Merhi1, Jacques Auger2, Francine Rendu1, Brigitte Bauvois11UMR 7131 UPMC Paris Universitas/CNRS, Groupe Hospitalier Broussais-HEGP, Paris, France; 2University F. Rabelais, IRBI, UPRESA CNRS 6035, Tours, FranceAbstract: Epidemiologic studies support the premise that Allium vegetables may lower the risk of cancers. The beneficial effects appear related to the organosulfur products generated upon processing of Allium. Leukemia cells from patients with acute myeloid leukemia (AML) display high proliferative capacity and have a reduced capacity of undergoing apoptosis and maturation. Whether the sulfur-containing molecules Thiosulfinates (TS), diallyl TS (All2TS), dipropyl TS (Pr2TS) and dimethyl TS (Me2TS), are able to exert chemopreventative activity against AML is presently unknown. The present study was an evaluation of proliferation, cytotoxicity, differentiation and secretion of AML cell lines (U937, NB4, HL-60, MonoMac-6) in response to treatment with these TS and their related sulfides (diallylsulfide, diallyl disulfide, dipropyl disulfide, dimethyl disulfide). As assessed by flow cytometry, ELISA, gelatin zymogaphy and RT-PCR, we showed that Pr2TS and Me2TS, but not All2TS and sulfides, 1) inhibited cell proliferation in dose- and time-dependent manner and this process was neither due to cytotoxicity nor apoptosis, 2) induced macrophage maturation, and 3) inhibited the levels of secreted MMP-9 (protein and activity) and TNF-α protein, without altering mRNA levels. By establishing for the first time that Pr2TS and Me2TS affect proliferation, differentiation and secretion of leukemic cell lines, this study provides the opportunity to explore the potential efficiency of these molecules in AML.Keywords: acute myeloid leukemia, Thiosulfinate, proliferation, differentiation, matrix metalloproteinase-
-
Thiosulfinates modulate platelet activation by reaction with surface free sulfhydryls and internal thiol-containing proteins.
Platelets, 2007Co-Authors: Perrine Badol, Monique David-dufilho, Jacques Auger, Sidney W. Whiteheart, Francine RenduAbstract:Thiosulfinates are characteristic flavors of Allium vegetables, with a highly reactive S-S=O group, that we previously showed to inhibit platelet aggregation through calpain-dependent mechanisms. With the aim to clarify the mode of action of these redox phytochemicals, we studied their effect on extracellular free sulfhydryls in relation to their effect on platelet responses (Ca(2+) signals, release reaction, and a(IIb)beta(3) integrin activation state). At the platelet surface, Thiosulfinate dose-dependently increased the basal level of free sulfhydryls, independently of protein disulfide isomerase activity. This generation of new free sulfhydryls was associated with: (i) a three fold increase in labeling of resting platelets with an anti ligand-induced binding site antibody and (ii) marked inhibition of subsequent a(IIb)beta(3) activation by agonists. Thiosulfinates increased the basal intracellular Ca(2+) level of platelets. In activated platelets, they markedly inhibited the Ca(2+) mobilization independently of the external Ca(2+), the calpain-induced SNAP-23 cleavage and the granule release. In platelet free systems, Thiosulfinates inhibited the activity of purified calpain and the free sulfhydryl of glutathione without any reducing properties on disulfides. The results demonstrate for the first time that Thiosulfinates rapidly interact with sulfhydryls both at the platelet surface and inside the cell on intracellular cysteine-proteins, especially calpain. Inhibition of free cysteine and glutathione in whole blood may also contribute to their anti-aggregant properties. Such sulfur compounds are of interest for the development of a new class of antithrombotic agents.
-
Thiosulfinates modulate platelet activation by reaction with surface free sulfhydryls and internal thiol-containing proteins.
Platelets, 2007Co-Authors: Perrine Badol, Monique David-dufilho, Jacques Auger, Sidney W. Whiteheart, Francine RenduAbstract:Thiosulfinates are characteristic flavors of Allium vegetables, with a highly reactive S-S=O group, that we previously showed to inhibit platelet aggregation through calpain-dependent mechanisms. With the aim to clarify the mode of action of these redox phytochemicals, we studied their effect on extracellular free sulfhydryls in relation to their effect on platelet responses (Ca2+ signals, release reaction, and aIIb3 integrin activation state). At the platelet surface, Thiosulfinate dose-dependently increased the basal level of free sulfhydryls, independently of protein disulfide isomerase activity. This generation of new free sulfhydryls was associated with: (i) a three fold increase in labeling of resting platelets with an anti ligand-induced binding site antibody and (ii) marked inhibition of subsequent aIIb3 activation by agonists. Thiosulfinates increased the basal intracellular Ca2+ level of platelets. In activated platelets, they markedly inhibited the Ca2+ mobilization independently of the external Ca2+, the calpain-induced SNAP-23 cleavage and the granule release. In platelet free systems, Thiosulfinates inhibited the activity of purified calpain and the free sulfhydryl of glutathione without any reducing properties on disulfides. The results demonstrate for the first time that Thiosulfinates rapidly interact with sulfhydryls both at the platelet surface and inside the cell on intracellular cysteine-proteins, especially calpain. Inhibition of free cysteine and glutathione in whole blood may also contribute to their anti-aggregant properties. Such sulfur compounds are of interest for the development of a new class of antithrombotic agents.
Péter Nagy - One of the best experts on this subject based on the ideXlab platform.
-
Reactive sulfur species: kinetics and mechanisms of the reaction of cysteine Thiosulfinate ester with cysteine to give cysteine sulfenic acid.
Journal of Organic Chemistry, 2007Co-Authors: Péter Nagy, Kelemu Lemma, Michael T. AshbyAbstract:The kinetics and mechanisms of the reaction of cysteine with cysteine Thiosulfinate ester in aqueous solution have been studied by stopped-flow spectrophotometry between pH 6 and 14. Two reaction pathways were observed for pH > 12: (1) an essentially pH-independent nucleophilic attack of cysteinate on cysteine Thiosulfinate ester, and (2) a pH-dependent fast equilibrium protonation of cysteine sulfenate that is followed by rate-limiting comproportionation of cysteine sulfenic acid with cysteinate to give cystine. For 6 < pH < 12, the rate-determining reaction between cysteinate and cysteine Thiosulfinate ester becomes pH-dependent due to the protonation of their amine groups. Hydrolysis of cysteine Thiosulfinate ester does not play a role in the aforementioned mechanisms because the rate-determining nucleophilic attack by hydroxide is relatively slow.
-
Reactive sulfur species: kinetics and mechanisms of the oxidation of cysteine by hypohalous acid to give cysteine sulfenic acid.
Journal of the American Chemical Society, 2007Co-Authors: Péter Nagy, Michael T. AshbyAbstract:Cysteine sulfenic acid has been generated in alkaline aqueous solution by oxidation of cysteine with hypohalous acid (HOX, X = Cl or Br). The kinetics and mechanisms of the oxidation reaction and the subsequent reactions of cysteine sulfenic acid have been studied by stopped-flow spectrophotometry between pH 10 and 14. Two reaction pathways were observed: (1) below pH 12, the condensation of two sulfenic acids to give cysteine Thiosulfinate ester followed by the nucleophilic attack of cysteinate on cysteine Thiosulfinate ester and (2) above pH 10, a pH-dependent fast equilibrium protonation of cysteine sulfenate that is followed by rate-limiting comproportionation of cysteine sulfenic acid with cysteinate to give cystine. The observation of the first reaction suggests that the condensation of cysteine sulfenic acid to give cysteine Thiosulfinate ester can be competitive with the reaction of cysteine sulfenic acid with cysteine.
-
Reactive Sulfur Species: Kinetics and Mechanism of the Hydrolysis of Cysteine Thiosulfinate Ester
Chemical research in toxicology, 2007Co-Authors: Péter Nagy, Michael T. AshbyAbstract:The kinetics and mechanisms of the hydrolysis of cysteine Thiosulfinate ester (CyS(═O)SCyx−, x = 0–2) have been investigated by stopped-flow spectrophotometry between pH 6 and pH 14. The rate-limiting reaction of hydroxide is observed for pH < 13. More complicated kinetics are observed above pH 13, where the hydrolysis of CyS(═O)SCy2− can be fast relative to subsequent reactions. The eventual products of hydrolysis are a 1:1 molar ratio of cystine (CySSCy) and cysteine sufinic acid (CySO2H) under all reaction conditions. The rate of hydrolysis is dependent upon the proton state of CyS(═O)SCyx−. Furthermore, cysteine thiosulfonate ester (CyS(═O)2SCy) was observed as an intermediate during the hydrolysis of CyS(═O)SCyx− at lower pH. CyS(═O)2SCy eventually hydrolyzes to give stoichiometric amounts of CySSCy and CySO2H. However, CySO2H is observed under some conditions for which hydrolysis of CyS(═O)2SCy is relatively slow, thus suggesting multiple hydrolysis pathways for CyS(═O)SCyx−. The mechanism up to the...
Kirk L. Parkin - One of the best experts on this subject based on the ideXlab platform.
-
In vitro stability and chemical reactivity of Thiosulfinates.
Journal of agricultural and food chemistry, 2002Co-Authors: Cunxi Shen, Hang Xiao, Kirk L. ParkinAbstract:A model reaction system was used to generate pure Thiosulfinates (3) from S-alk(en)yl-l-cysteine sulfoxides (1) to facilitate studies on the intrinsic pH and thermal sensitivities of individual Thiosulfinate species. Thiosulfinate decay could be characterized as first-order processes over the pH range of 1.2−9.0 and at 20−80 °C. The stability of Thiosulfinates was greatest at pH 4.5−5.5, followed by pH 1.2, pH 6.5−7.5, and pH 8.0−9.0. Thiosulfinates with longer and saturated alk(en)yl groups were generally more stable than those with shorter and unsaturated alk(en)yl groups. Thiosulfinates underwent thioalkyl-exchange reactions at pH 8−9 without loss of total Thiosulfinate levels within 60−90 min at 20 °C. Keywords: Thiosulfinates; Allium; organosulfur; stability; reactivity; thioalk(en)yl-exchange
-
Fate and kinetic modeling of reactivity of alkanesulfenic acids and Thiosulfinates in model systems and onion homogenates.
Journal of agricultural and food chemistry, 2002Co-Authors: Cunxi Shen, Zongxuan Hong, Kirk L. ParkinAbstract:The dynamic changes in Thiosulfinate profiles were studied in reaction systems containing a crude onion alliinase, S-alk(en)yl-l-cysteine sulfoxide substrates (1) and preformed Thiosulfinates (4). Regioisomeric excesses of one of two possible heterologous 4 species (RS(O)SR‘, where R ≠ R‘) could be manipulated under conditions where alliinase, 1, and 4 levels were varied. Regioisomeric excesses could be explained by a Thiosulfinate (4)/alkanesulfenic acid (2) trapping mechanism, with the greatest control over product profile governed by the rate of 2 generation in the system. The series of reactions existing in this dynamic reaction system was kinetically modeled with reasonable fits to the experimental data. The application of the 4/2 trapping strategy to manipulate Thiosulfinate and related organosulfur product profiles in diluted onion homogenates was demonstrated using exogenous MeS(O)SMe (4a), PrS(O)SPr (4c), and AllS(O)SAll (4d) as the preformed Thiosulfinate. Keywords: Thiosulfinate; alkanesulfenic...
-
Antioxidant functions of selected allium Thiosulfinates and S-alk(en)yl-L-cysteine sulfoxides.
Journal of agricultural and food chemistry, 2002Co-Authors: Hang Xiao, Kirk L. ParkinAbstract:Pure Thiosulfinates, R−S(O)S−R (2), where R = Me (2a), Pr (2b), or All (2c), at levels up to 4 mM were not capable of scavenging hydrogen peroxide or superoxide anion. Relative to standard antioxidants (ascorbic acid, n-propyl gallate, butylated hydroxytoluene, Trolox, and reduced glutathione), these Thiosulfinates were 1−3 orders of magnitude less efficient at reducing 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, 0.5−2 orders of magnitude less efficient at quenching singlet oxygen, and about equally effective at scavenging hydroxyl radical. Generally, AllS(O)SAll (2c) was the most effective and PrS(O)SPr (2b) was the least effective Thiosulfinate in these assays, except that MeS(O)SMe (2a) exhibited no quenching effect toward singlet oxygen. These Thiosulfinates were also incapable at levels up to 0.1 mM (where they were toxic) of in vitro induction of quinone reductase (QR) in murine hepatoma (hepa 1c1c7) cells. However, S-1-propenyl-l-cysteine sulfoxide (isoalliin, 1a) and cycloalliin (3) induced QR i...
-
In Vitro Biogeneration of Pure Thiosulfinates and Propanethial-S-oxide
Journal of agricultural and food chemistry, 2000Co-Authors: Cunxi Shen, Kirk L. ParkinAbstract:A model reaction system was developed for generating pure Thiosulfinates and propanethial-S-oxide (PTSO) using an isolated alliinase (EC 4.4.1.4) and isolated or synthetic alk(en)yl-l-cysteine sulfoxides (ACSO). Reaction yields ranged from 30 to 60% after 3 h at 21−23 °C, and organosulfur reaction products were extracted into CHCl3 to yield product preparations of controlled composition. A pure Thiosulfinate or PTSO was derived from a single ACSO, and a preparation containing a mixture of four Thiosulfinate species was derived from reaction mixtures employing binary ACSO substrate systems. Identities of homologous Thiosulfinates and PTSO were confirmed by 1H NMR. This approach has the potential to be used as a preparative tool for yielding pure Thiosulfinates and PTSO to facilitate the study of chemical and biological properties of this group of compounds or as a means to study the dynamics of organosulfur chemistry in preparations from Allium spp. Keywords: Allium; Thiosulfinates; propanethial-S-oxide; b...
-
Relationship between Thiosulfinates and pink discoloration in onion extracts, as influenced by pH
Food Chemistry, 1998Co-Authors: Chen-hsien Lee, Kirk L. ParkinAbstract:Abstract The influence of immediate and delayed pH control, and added S-methyl-L-cysteine sulfoxide (MCSO) on the progress of pink discoloration in relation to the fate of Thiosulfinates in extracts of yellow onion (Allium cepa) bulbs was evaluated over an incubation period of about 3 weeks at 21–24°C. Greatest discoloration occurred in extracts prepared with immediate pH control at 6.1, and least discoloration occurred at pH 3.2, over the pH range of 3.2–6.1. Initial Thiosulfinate levels, in descending order of abundance, occurred at pH 6.1 > 5.0 > 4.2 > 3.2 for extracts subject to immediate pH control. However, over 21 days incubation, the lowest residual levels (ranging 20–60% of maximum levels) were observed for extracts adjusted to pH 3.2 and 6.1. Extracts subject to delayed (10 min after tissue disruption) pH control (initial extract pH of 5.2–5.4) displayed the greatest extent of discoloration, in descending order, at pH 4.0 > 5.0, 6.0 > 3.0. In these samples, initial Thiosulfinate levels were similar and the greatest residual Thiosulfinate levels over the 21-day incubation period were observed at pH 3.0 and 4.0 (about 50% of maximum levels), with the lowest residual levels observed for extracts adjusted to pH 6.0 (about 20% of maximum levels). Tissue extracts supplemented with 9- to 18-fold excess MCSO were subject to modest increases in both extent of discoloration and Thiosulfinate levels.
Qi Yang - One of the best experts on this subject based on the ideXlab platform.
-
The inhibitory effect of Thiosulfinate on volatile fatty acid and hydrogen production from anaerobic co-fermentation of food waste and waste activated sludge.
Bioresource technology, 2019Co-Authors: Ziletao Tao, Fubing Yao, Xiaoding Huang, Qi Yang, Shengjie Chen, Xuran Liu, Dongbo WangAbstract:Abstract Thiosulfinate, a nature antibiotic, existed in all parts of Allium thereby accumulating in kitchen waste vastly. However, few literatures were available related to its influence on volatile fatty acids (VFA) and hydrogen production when kitchen waste digestion technology was applied. This study aimed to explore the inhibitory effect and the relevant mechanism. Experimental results showed that the hydrogen accumulation decreased from 23.2 ± 0.8 to 8.2 ± 0.1 mL/g VSS (volatile suspended solid) and maximal total VFA yield decreased from 765.7 ± 21.2 to 376.4 ± 21.7 mg COD (chemical oxygen demand)/g VSS when the dosage of Thiosulfinate increased from 0 to 12.5 µg/g VSS. The mechanism study indicated, compared with control group, that the butyric acid decreased from 59% to 20.1% of total VFA yield when reactor in present of 12.5 µg/g VSS Thiosulfinate. Moreover, the relative activities of functional enzymes were inhibited 73.4% (butyryl-CoA) and 72.7% (NADH), respectively.
-
The effects of Thiosulfinates on methane production from anaerobic co-digestion of waste activated sludge and food waste and mitigate method.
Journal of hazardous materials, 2019Co-Authors: Ziletao Tao, Dongbo Wang, Fubing Yao, Xiaoding Huang, Zhuo Chen, Qi YangAbstract:Abstract Thiosulfinates, a natural antibiotic, existed in all parts of Allium, therefore might be accumulated in large amounts in food waste (FW). FW was often added into waste activated sludge (WAS) anaerobic digestion process as a kind of supplement for nutrition balance. However, the impact of Thiosulfinates on methane production and the possible approach to mitigate its inhibition on the co-digestion process could be available in few literatures. This work was carried out in a series of batch experiment at pH 7.0 ± 0.2 and 35 ± 1.0 ℃ to promote the further understanding of this process. The experimental results showed that the methane accumulation decreased from 270.6 ± 13.4 to 16.7 ± 7.0 mL/g VSS (volatile suspended solids) when the initial concentration of Thiosulfinates increased from 0 to 2.5 μg/g VSS. The activities of functional enzymes (F420 and CoM) were inhibited by 99.06% and 99.82% compared with control group when reactor contained 2.5 μg/g VSS Thiosulfinates. Furthermore, different temperature, pH, and combination pretreat were applied to impair the inhibition of Thiosulfinate. Compared with no pretreatment group, methane yield was increased by 2.26, 32.18 and 42.2-fold, respectively which group was under pretreatment method of heat (100 ℃), alkali (pH 9) and combination.
