Enzymatic catalysis of the reversible sulfitolysis of glutathione disulfide and the biological reduction of thiosulfate esters (original) (raw)
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Thiosulfoxide (sulfane) sulfur: new chemistry and new regulatory roles in biology
Molecules (Basel, Switzerland), 2014
The understanding of sulfur bonding is undergoing change. Old theories on hypervalency of sulfur and the nature of the chalcogen-chalcogen bond are now questioned. At the same time, there is a rapidly expanding literature on the effects of sulfur in regulating biological systems. The two fields are inter-related because the new understanding of the thiosulfoxide bond helps to explain the newfound roles of sulfur in biology. This review examines the nature of thiosulfoxide (sulfane, S0) sulfur, the history of its regulatory role, its generation in biological systems, and its functions in cells. The functions include synthesis of cofactors (molybdenum cofactor, iron-sulfur clusters), sulfuration of tRNA, modulation of enzyme activities, and regulating the redox environment by several mechanisms (including the enhancement of the reductive capacity of glutathione). A brief review of the analogous form of selenium suggests that the toxicity of selenium may be due to over-reduction caused...
Glutathione homeostasis and redox-regulation by sulfhydryl groups
Photosynthesis Research, 2005
Continuous control of metabolism and developmental processes is a key feature of live cells. Cysteine thiol residues of proteins are both exceptionally useful in terms of structural and regulatory aspects, but at the same time exceptionally vulnerable to oxidation. Conserved cysteines thus are highly important for the function of metabolic enzymes and for signaling processes underlying responses to environmental factors. The underlying mechanism for the central role of thiol-mediated redox control in cellular metabolism is the ability of the cysteine-thiols to reversibly change their redox state followed by changes of structural, catalytic or regulatory functions. The cellular glutathione/glutathione disulfide redox buffer is present in cells at millimolar concentrations and forms one major basis of redox homeostasis by which protein thiols can maintain their redox state or oxidized protein thiols can be reverted to their reduced state. Besides acting as redox buffer, glutathione also acts as an electron donor for both scavenging of reactive oxygen, e.g. from photosynthesis and respiration, and metabolic reactions such as reduction of hydroperoxides and lipidperoxides or sulfate assimilation. The central role of glutathione is further emphasized by its involvement in signaling processes and the crosstalk of redox signaling processes with other means of signaling including protein glutathionylation and control of transcription factors. The present review aims at highlighting the key functions of glutathione in thiol-mediated redox control and its interplay with other protein-thiol-based redox systems.
Biochemistry, 1978
An enzyme catalyzing thiol-disulfide interchange of glutathione and disulfides and the reaction between glutathione and thiosulfate esters has been purified 40 000-fold from rat liver cytosol. The enzyme, named thioltransferase (Askelöf, P., Axelsson, K., Eriksson, S., & Mannervik, B. (1974) FEBS Lett. 38, 263--267), was homogeneous in several electrophoretic systems, had an isoelectric point at pH 9.6, and contained 8.6% (w/w) carbohydrate. The catalytic activity had a distinct optimum at pH 7.5. A series of substrates was tested at a constant glutathione level; the kcat values (at 4mM glutathione) were all in the range of about 10(4) min-1. The substrates included mixed disulfides of glutathione, other low-molecular-weight disulfides, S-sulfocysteine and S-sulfoglutathione, and peptide disulfides such as insulin, oxytocin, ribonuclease, and the mixed disulfide of glutathione and egg-white lysozyme. The enzymatic reaction was inhibited by an excess of glutathione (greater than 4mM).
Biochemical Pharmacology, 1975
Abstraet-In earlier work*, we have studied a labile enzyme activity catalyzing an exchange between thiol and acceptor. G~utathione (GSH) was used as the thiol and a number of low molecular weight substances such as cystine and GSH-disulfide derivatives, S-sulfocysteine (CySSO,H), S-sulfoglutathione and 5,5'dithiobis(2-nitrobenzoate) (DTNB) were used as acceptor substrates in the thiol transfer reaction. This broad substrate specificity led us to the tentative suggestion that thiamine disulfide derivatives also were acceptor substrates to the thioltransferaset activity, which is confirmed in this study. The methods used for the resolution ofenzymes and substrate specificity were: (1) isoelectric focusing, (2) CM-cellulose chromatography, (3) labelling of the thioltransferase with ["S]GSH, (4) gel filtration on Bio-Gel P-150, and (5) investigation of ratios of the specific activities of GSH-linked enzymes in different tissues. Generally it was found that bovine tissue had higher specific thioitransfera~ activity than rat tissue. GSH S-aryltransferase (EC 2.5.1.13) had quite different activity ratios from those obtained with the enzyme involved in cystine and thiamine disulfide reduction. This result, and dissimilar chromatographic behavior, indicate that GSH S-aryltransferase is not involved in disulfide reduction.
TheScientificWorldJournal, 2012
Toxicity of drugs and radiation in the cells is largely dependent on the level of thiols. In the present studies, an attempt has been made to inhibit γ-glutamyl transpeptidase (γGT) activity in EAT-bearing animals tissue. We have expected that administration of γGT inhibitors: acivicin and 1,2,3,4-tetrahydroisoquinoline (TIQ) may influence GSH/γ-glutamyl transpeptidase (γGT) system in the regulation of cysteine concentration and anaerobic cysteine metabolism in normal and cancer cells. Development of Ehrlich ascites tumor in mice enhances peroxidative processes, diminishes levels of nonprotein thiols (NPSH) and sulfane sulfur, and lowers activities of enzymes involved in its formation and transfer in the liver and kidney. Although γGT inhibitors further decrease NPSH level, they increase cysteine and sulfane sulfur levels. This means that upon γGT inhibition, cysteine can be efficiently acquired by normal liver and kidney cells via another pathway, that is so productive that sulfane...
Effects of sulfite on glutathione S-sulfonate and the glutathione status of lung cells
Chemico-Biological Interactions, 1989
A mechanistic study was performed to elucidate the biochemical events connected with the cocarcinogenic effect of sulfur dioxide (S02). Glutathione S-sulfonate (GSS03H), a competitive inhibitor of the glutathione S-transferases, forms in lung cells exposed in culture to sulfite, the hydrated form of S02. Changes in glutathione status (total GSH) were also observed during a 1-h exposure. Some cells were pretreated with 1,3-bis(2-chloroethyl)-l-nitrosourea (BCNU) to inhibit glutathione reductase. In human lung cells GSSO3H formed in a concentration-dependent manner, while glutathione (GSH) increased and glutathione disulfide (GSSG) decreased as the extraceUular sulfite concentration was increased from 0 to 20 raM. The ratio of GSH/ GSSG increased greater than 5-fold and the GSH/GSSO3H ratio decreased to 10 with increasing sulfite concentration. GSSO3H formed in rat lung cells exposed to sulfite, with no detectable effect on GSH and GSSG. GSSOsH also formed from cellular GSH mixed disulfides. GSSO3H formed rapidly, reaching its maximum value in 15 min. The viability of both cell types was unaffected except at 20 mM sulfite. GSSO3H incubated with human lung cells did not affect cellular viability. BCNU inhibited cellular GSSO3H reductase to the same extent as GSSG reductase. These results indicate that GSSO3H is formed in cells exposed to sulfite, and could be the active metabolite of sulfite responsible for the cocarcinogenic effect of SO 2 by inhibiting conjugation of electrophiles by GSH.
Thioltransferase is a specific glutathionyl mixed-disulfide oxidoreductase
Biochemistry, 1993
To study the substrate specificity and mechanism of thioltransferase (TTase) catalysis, we have used 14C-and 35S-radiolabeled mixed disulfides of cysteine and glutathione (GSH) with various cysteinecontaining proteins. These protein mixed disulfide substrates were incubated with glutathione, glutathione disulfide (GSSG) reductase, and NADPH in the presence or absence of thioltransferase. Glutathionedependent reduction of protein mixed disulfides was monitored both by release of trichloroacetic acid soluble radiolabel and by formation of GSSG in an NADPH-linked spectrophotometric assay. GSHdependent dethiolation of [35S]glutathione-papain mixed disulfide (papainSSG) and the corresponding bovine serum albumin mixed disulfide (BSASSG) were catalyzed by thioltransferase (from human red blood cells) as shown by the radiolabel assay, and equivalent rates were measured by the spectrophotometric