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Histone lysine methylation is a key epigenetic modification that regulates eukaryotic transcription. In Saccharomyces cerevisiae, it is controlled by a reduced but evolutionarily conserved suite of methyltransferase (Set1p, Set2p, Dot1p, and Set5p) and demethylase (Jhd1p, Jhd2p, Rph1p, and Gis1p) enzymes. Many of these enzymes are extensively phosphorylated in vivo; however, the functions of almost all phosphosites remain unknown. Here, we comprehensively analyse the phosphoregulation of the yeast histone methylation network by functionally investigating 40 phosphosites on six enzymes. A total of 82 genomically-edited S. cerevisiae strains were generated through mutagenesis of sites to aspartate as a phosphomimetic or alanine as a phosphonull. These phosphosite mutants were screened for changes in native H3K4, H3K36, and H3K79 methylation levels, and for sensitivity to environmental stress conditions. For methyltransferase Set2p, we found that phosphorylation at threonine 127 significantly decreased H3K36 methylation in vivo, and that an N-terminal phosphorylation cluster at serine residues 6, 8, and 10 is required for the diamide stress response. Proteomic analysis of Set2p phosphosite mutants revealed a specific downregulation of membrane-associated proteins and processes, consistent with changes brought about by SET2 deletion and the sensitivity of mutants to diamide. For demethylase Jhd1p, we found that its sole phosphorylation site at serine 44 is required for the cold stress response. This study represents the first systematic investigation into the phosphoregulation of the epigenetic network in any eukaryote, and shows that phosphosites on histone methylation enzymes are required for a normal cellular response to stress in S. cerevisiae.

El glutatión (GSH) es el antioxidante no enzimático más abundante en las células de mamífero, constituido por un tripéptido glutamato-cisteína-glicina. Gracias al grupo sulfhidrilo de la cisteína, actúa como donador de electrones para reducir enlaces disulfuro entre cisteínas, reaccionar con especies reactivas de oxígeno mediante su grupo tiol oxidándose a glutatión disulfuro (GSSG)- o para convertir el peróxido de hidrógeno en dos moléculas de agua inocua para la célula mediante la acción de la enzima glutatión peroxidasa, entre otros antioxidantes enzimáticos. No obstante, en la actualidad se están estudiando otras funciones relacionadas con el GSH como es el caso de las modificaciones postraduccionales glutationilación de proteínas o su relación con la regulación epigenética, dado que algunas moléculas y metabolitos intermediarios de la síntesis de glutatión lo son a su vez de las rutas de metilación de ADN e histonas. Con la finalidad de analizar la relación entre el nivel de estado redox celular debido a niveles de GSH y la alteración de modificaciones postraduccionales en histonas, se ha optimizado un protocolo para disminuir la concentración de GSH celular mediante tratamiento con diamida en células HeLa, y se ha analizado mediante citometría de flujo, fluorimetría y microscopía de fluorescencia. En algunas patologías de carácter progeroide, caracterizadas por cursar con envejecimiento prematuro y en las que se ha observado alteraciones en la estructura de la cromatina, se ha comprobado que uno de los factores de relevancia es el estrés oxidativo que padecen a nivel celular, además de mostrar niveles disminuidos de GSH. Por esta razón, paralelamente se ha trabajado con líneas de fibroblastos humanos dos controles y un paciente de la patología progeroide síndrome de Werner analizando tanto enzimas antioxidantes, como modificaciones en histonas., Glutathione (GSH) is the most abundant non-enzymatic antioxidant in mammalian cells, constituted by a glutamate-cysteine-glycine tripeptide. Thanks to its sulfhydryl residue, acts as an electron donor to reduce disulfide bonds between cysteines, to react with reactive oxygen species by means of its thiol group, or to convert hydrogen peroxide into two molecules of water -safe for the cell- through the action of the enzyme glutathione peroxidase, among other antioxidant enzymes. However, other functions related to GSH are currently being studied, as is the case of post-translational modifications protein glutathionylation- or its relation to epigenetic regulation, since some molecules and intermediate metabolites in the synthesis of glutathione are also involved in DNA and protein methylation pathways. In order to analyze the relationship between the cellular redox state due to GSH levels and alterations in histone posttranslational modifications, a treatment has been optimized to reduce cellular GSH concentration by treatment with diamide in HeLa cells, and the effect has been analyzed by flow cytometry, fluorimetry, and fluorescence microscopy. In some pathology with progeroid features, characterized by premature ageing and in which alterations in chromatin structure have been observed, it has been shown that one of the relevant factors is the oxidative stress they show at the cellular level, besides having reduced levels of GSH. For this reason, in parallel we have worked with human fibroblast cell lines two controls and a patient with Werner syndrome analyzing antioxidant enzymes and modifications in histones.

El glutatión (GSH) es el antioxidante no enzimático más abundante en las células de mamífero, constituido por un tripéptido glutamato-cisteína-glicina. Gracias al grupo sulfhidrilo de la cisteína, actúa como donador de electrones para reducir enlaces disulfuro entre cisteínas, reaccionar con especies reactivas de oxígeno mediante su grupo tiol oxidándose a glutatión disulfuro (GSSG)- o para convertir el peróxido de hidrógeno en dos moléculas de agua inocua para la célula mediante la acción de la enzima glutatión peroxidasa, entre otros antioxidantes enzimáticos. No obstante, en la actualidad se están estudiando otras funciones relacionadas con el GSH como es el caso de las modificaciones postraduccionales glutationilación de proteínas o su relación con la regulación epigenética, dado que algunas moléculas y metabolitos intermediarios de la síntesis de glutatión lo son a su vez de las rutas de metilación de ADN e histonas. Con la finalidad de analizar la relación entre el nivel de estado redox celular debido a niveles de GSH y la alteración de modificaciones postraduccionales en histonas, se ha optimizado un protocolo para disminuir la concentración de GSH celular mediante tratamiento con diamida en células HeLa, y se ha analizado mediante citometría de flujo, fluorimetría y microscopía de fluorescencia. En algunas patologías de carácter progeroide, caracterizadas por cursar con envejecimiento prematuro y en las que se ha observado alteraciones en la estructura de la cromatina, se ha comprobado que uno de los factores de relevancia es el estrés oxidativo que padecen a nivel celular, además de mostrar niveles disminuidos de GSH. Por esta razón, paralelamente se ha trabajado con líneas de fibroblastos humanos dos controles y un paciente de la patología progeroide síndrome de Werner analizando tanto enzimas antioxidantes, como modificaciones en histonas., Glutathione (GSH) is the most abundant non-enzymatic antioxidant in mammalian cells, constituted by a glutamate-cysteine-glycine tripeptide. Thanks to its sulfhydryl residue, acts as an electron donor to reduce disulfide bonds between cysteines, to react with reactive oxygen species by means of its thiol group, or to convert hydrogen peroxide into two molecules of water -safe for the cell- through the action of the enzyme glutathione peroxidase, among other antioxidant enzymes. However, other functions related to GSH are currently being studied, as is the case of post-translational modifications protein glutathionylation- or its relation to epigenetic regulation, since some molecules and intermediate metabolites in the synthesis of glutathione are also involved in DNA and protein methylation pathways. In order to analyze the relationship between the cellular redox state due to GSH levels and alterations in histone posttranslational modifications, a treatment has been optimized to reduce cellular GSH concentration by treatment with diamide in HeLa cells, and the effect has been analyzed by flow cytometry, fluorimetry, and fluorescence microscopy. In some pathology with progeroid features, characterized by premature ageing and in which alterations in chromatin structure have been observed, it has been shown that one of the relevant factors is the oxidative stress they show at the cellular level, besides having reduced levels of GSH. For this reason, in parallel we have worked with human fibroblast cell lines two controls and a patient with Werner syndrome analyzing antioxidant enzymes and modifications in histones.

El glutatión (GSH) es el antioxidante no enzimático más abundante en las células de mamífero, constituido por un tripéptido glutamato-cisteína-glicina. Gracias al grupo sulfhidrilo de la cisteína, actúa como donador de electrones para reducir enlaces disulfuro entre cisteínas, reaccionar con especies reactivas de oxígeno mediante su grupo tiol oxidándose a glutatión disulfuro (GSSG)- o para convertir el peróxido de hidrógeno en dos moléculas de agua inocua para la célula mediante la acción de la enzima glutatión peroxidasa, entre otros antioxidantes enzimáticos. No obstante, en la actualidad se están estudiando otras funciones relacionadas con el GSH como es el caso de las modificaciones postraduccionales glutationilación de proteínas o su relación con la regulación epigenética, dado que algunas moléculas y metabolitos intermediarios de la síntesis de glutatión lo son a su vez de las rutas de metilación de ADN e histonas. Con la finalidad de analizar la relación entre el nivel de estado redox celular debido a niveles de GSH y la alteración de modificaciones postraduccionales en histonas, se ha optimizado un protocolo para disminuir la concentración de GSH celular mediante tratamiento con diamida en células HeLa, y se ha analizado mediante citometría de flujo, fluorimetría y microscopía de fluorescencia. En algunas patologías de carácter progeroide, caracterizadas por cursar con envejecimiento prematuro y en las que se ha observado alteraciones en la estructura de la cromatina, se ha comprobado que uno de los factores de relevancia es el estrés oxidativo que padecen a nivel celular, además de mostrar niveles disminuidos de GSH. Por esta razón, paralelamente se ha trabajado con líneas de fibroblastos humanos dos controles y un paciente de la patología progeroide síndrome de Werner analizando tanto enzimas antioxidantes, como modificaciones en histonas., Glutathione (GSH) is the most abundant non-enzymatic antioxidant in mammalian cells, constituted by a glutamate-cysteine-glycine tripeptide. Thanks to its sulfhydryl residue, acts as an electron donor to reduce disulfide bonds between cysteines, to react with reactive oxygen species by means of its thiol group, or to convert hydrogen peroxide into two molecules of water -safe for the cell- through the action of the enzyme glutathione peroxidase, among other antioxidant enzymes. However, other functions related to GSH are currently being studied, as is the case of post-translational modifications protein glutathionylation- or its relation to epigenetic regulation, since some molecules and intermediate metabolites in the synthesis of glutathione are also involved in DNA and protein methylation pathways. In order to analyze the relationship between the cellular redox state due to GSH levels and alterations in histone posttranslational modifications, a treatment has been optimized to reduce cellular GSH concentration by treatment with diamide in HeLa cells, and the effect has been analyzed by flow cytometry, fluorimetry, and fluorescence microscopy. In some pathology with progeroid features, characterized by premature ageing and in which alterations in chromatin structure have been observed, it has been shown that one of the relevant factors is the oxidative stress they show at the cellular level, besides having reduced levels of GSH. For this reason, in parallel we have worked with human fibroblast cell lines two controls and a patient with Werner syndrome analyzing antioxidant enzymes and modifications in histones.

El glutatión (GSH) es el antioxidante no enzimático más abundante en las células de mamífero, constituido por un tripéptido glutamato-cisteína-glicina. Gracias al grupo sulfhidrilo de la cisteína, actúa como donador de electrones para reducir enlaces disulfuro entre cisteínas, reaccionar con especies reactivas de oxígeno mediante su grupo tiol oxidándose a glutatión disulfuro (GSSG)- o para convertir el peróxido de hidrógeno en dos moléculas de agua inocua para la célula mediante la acción de la enzima glutatión peroxidasa, entre otros antioxidantes enzimáticos. No obstante, en la actualidad se están estudiando otras funciones relacionadas con el GSH como es el caso de las modificaciones postraduccionales glutationilación de proteínas o su relación con la regulación epigenética, dado que algunas moléculas y metabolitos intermediarios de la síntesis de glutatión lo son a su vez de las rutas de metilación de ADN e histonas. Con la finalidad de analizar la relación entre el nivel de estado redox celular debido a niveles de GSH y la alteración de modificaciones postraduccionales en histonas, se ha optimizado un protocolo para disminuir la concentración de GSH celular mediante tratamiento con diamida en células HeLa, y se ha analizado mediante citometría de flujo, fluorimetría y microscopía de fluorescencia. En algunas patologías de carácter progeroide, caracterizadas por cursar con envejecimiento prematuro y en las que se ha observado alteraciones en la estructura de la cromatina, se ha comprobado que uno de los factores de relevancia es el estrés oxidativo que padecen a nivel celular, además de mostrar niveles disminuidos de GSH. Por esta razón, paralelamente se ha trabajado con líneas de fibroblastos humanos dos controles y un paciente de la patología progeroide síndrome de Werner analizando tanto enzimas antioxidantes, como modificaciones en histonas., Glutathione (GSH) is the most abundant non-enzymatic antioxidant in mammalian cells, constituted by a glutamate-cysteine-glycine tripeptide. Thanks to its sulfhydryl residue, acts as an electron donor to reduce disulfide bonds between cysteines, to react with reactive oxygen species by means of its thiol group, or to convert hydrogen peroxide into two molecules of water -safe for the cell- through the action of the enzyme glutathione peroxidase, among other antioxidant enzymes. However, other functions related to GSH are currently being studied, as is the case of post-translational modifications protein glutathionylation- or its relation to epigenetic regulation, since some molecules and intermediate metabolites in the synthesis of glutathione are also involved in DNA and protein methylation pathways. In order to analyze the relationship between the cellular redox state due to GSH levels and alterations in histone posttranslational modifications, a treatment has been optimized to reduce cellular GSH concentration by treatment with diamide in HeLa cells, and the effect has been analyzed by flow cytometry, fluorimetry, and fluorescence microscopy. In some pathology with progeroid features, characterized by premature ageing and in which alterations in chromatin structure have been observed, it has been shown that one of the relevant factors is the oxidative stress they show at the cellular level, besides having reduced levels of GSH. For this reason, in parallel we have worked with human fibroblast cell lines two controls and a patient with Werner syndrome analyzing antioxidant enzymes and modifications in histones.

Tématem diplomové práce je syntéza biologicky aktivních chirálních diamidů na bázi 1-(6-fluorbenzthiazol-2-yl)ethanaminu. Byla provedena literární rešerše s cílem nalézt vhodné postupy přípravy chirálních diamidů obsahující benzthiazolový blok a kyselinu 4-aminobenzoovou. Na základě této rešerše bylo v experimentální části vybranou modifikovanou metodou připraveno dvanáct nových sloučenin. Připravené diamidy byly charakterizovány bodem tání a NMR spektrometrií. Agarovou mikrodiluční metodou u nich bylastanovena minimální inhibiční koncentrace pro bakterieStaphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli a Enterococcus faecalis., The topic of this thesis is the synthesis of biological active diamides based on 1-(6-fluorobenzothiazole-2-yl)ethanamine. Literature search was conducted to find a suitable procedures for the preparation of chiral diamides containing bezothiazole block and an 4aminobenzoic acid. On the basis of this research was the experimental section selected by a modified method in new twelve compounds. Prepared diamides were characterized by melting point and NMR spectrometry. As an indication, they was determined a minimum inhibitory concentration againstbacteriaStaphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli a Enterococcus faecalis genusby using agar´s microdilution method., Fakulta chemicko-technologická, Ověření racemizace studovaných látek Izolace chromatografií, pozorování průběhu reakce Limity biologických aktivit, rozpustnost látek ve vodném prostředí

A new series of 1-[(1R)-1-(6-fluoro-1,3-benzothiazol-2-yl) ethyl]-3-substituted phenyl diamides were synthesized in vitro as potential antifungal agents. Chemical structures of the synthesised compounds were substantiated by IR, H-1, C-13, F-19 nuclear magnetic resonance spectra, high resolution mass spectrometry, elemental analysis and also by X-ray diffraction. In addition, the cytotoxicity of the most active compounds was investigated against cancer cell line (Jurkat) and one type of normal lung fibroblast cells (MRC-5) by (2,3-bis-(2-methoxy4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) tetrazolium salt reduction assay, propidium iodide flow cytometry assay and xCELLigence system allowing a label-free assessment of the cells proliferation. Compounds indicated as 11e, 11g, 11j, 11n and 11o, were the best of the series, showing minimum inhibitory concentration values of 6.25-50 mu g/mL against pathogenic strains Candida albicans HE 169, Candida tropicalis 31/HK and Candida parapsilosis p69. Moreover compounds 11e, 11g, 11j and 11o did not show any cytotoxic effect against human Jurkat and MRC-5 cells., Byla syntetizována nová řada 1 - [(lR) -l- (6-fluor-l, 3-benzothiazol-2-yl) ethyl] -3-substituovaných fenyl diamidů a testována in vitro jako potenciální antifungální činidla. Chemické struktury syntetizovaných sloučenin byly charakterizovány IR, H-1, C-13, F-19 NMR spektry, hmotnostní spektrometrií s vysokým rozlišením, elementární analýzou a také rentgenovou difrakcí. Kromě toho byla zkoumána cytotoxicita nejaktivnějších sloučenin proti rakovinové buněčné linii (Jurkat) a jednomu typu normálních plicních fibroblastových buněk (MRC-5) pomocí (2,3-bis- (2-methoxy4nitro-5- ) -2H-tetrazolium-5-karboxanilidu) testu redukce tetrazoliové soli, testu průtokové cytometrie a systému xCELLigence umožňujícím bezzásahové vyhodnocení proliferace buněk. Sloučeniny označené jako 11e, 11g, 11j, 11n a 11o byly nejlepší ze série, vykazující MIC hodnoty 6,25-50 ug / ml proti patogenním kmenům Candida albicans HE 169, Candida tropicalis 31 / HK a Candida parapsilosis p69 . Navíc sloučeniny 11e, 11g, 11j a 11o nevykazovaly žádný cytotoxický účinek proti buňkám, linií JURKAT a MRC-5.

[SPA] La polilla del tomate, Tuta absoluta, es en la actualidad una de las plagas más importantes a nivel mundial en el cultivo del tomate. El control químico tiene un papel fundamental en la gestión integrada de esta plaga. Clorantraniliprol es un insecticida perteneciente al grupo de las diamidas, muy empleado para el control de T. absoluta, ya que es compatible con los enemigos naturales y polinizadores. Sin embargo, están apareciendo casos de desarrollo de resistencia a este insecticida en algunas especies de lepidópteros. En este trabajo, se exponen los resultados obtenidos de la selección de dos poblaciones de T. absoluta a clorantraniliprol, obteniendo una población resistente de Sicilia, con CL50 de 147,2 ppm y otra de Murcia, con una CL50 de 29,1 ppm. [ENG] The tomato borer, Tuta absoluta, is currently one of the most important pests in tomato crops in the world. Chemical control plays a key role in the integrated management of this pest. Chlorantraniliprole is an insecticide belonging to the diamides group, widely used to manage T. absoluta, as it is compatible with natural enemies and pollinators. However, cases of resistance development to this insecticide are appearing in some lepidopteran species. In this study, the results of the selection for chlorantraniliprole of two populations of T. absoluta are presented, obtaining a resistant population from Sicily, with a LC50 of 147.2 ppm and another from Murcia, with a LC50 of 29.1 ppm.

Tématem diplomové práce je Syntéza a charakterizace biologicky aktivních diamidů na bázi 6-fluor-1,3-benzthiazolylalkylaminů. Byla provedena literární rešerše s cílem nalézt vhodné postupy přípravy diastereoizomerních diamidů obsahující bezthiazolový blok a aminokyselinu. Na základě této rešerše bylo v experimentální části vybranou modifikovanou metodou připraveno šestnáct nových sloučenin. Připravené diamidy byly charakterizovány bodem tání a NMR spektrometrií. Agarovou difúzní metodou u nich byla orientačně stanovena antifungální aktivita vůči kvasinkám rodu Candida., The topic of this thesis is the synthesis and characterization of biologically active diamides based on 6-fluoro-1,3-benzothiazolyl alkylamines. Literature search was conducted to find a suitable procedures for the preparation of diastereoisomeric diamides containing bezothiazole block and an amino acid. On the basis of this research was the experimental section selected by a modified method in new sixteen compounds. Prepared diamides were characterized by melting point and NMR spectrometry. As an indication, they were determined antifungal activity against Candida genus by using agar diffusion method., Ústav organické chemie a technologie, Recyklace THF, regenerace toluenu, jakou funkci má fluor na biologickou aktivitu,Metody pro přípravu amidů, antfungální aktivity - použití standardůVliv aktivita vs. struktura, Dokončená práce s úspěšnou obhajobou

Práce je zaměřena na syntézu, charakterizaci a biologickou aktivitu 2-hydroxy-N-(arylalkyl)benzamidů a jejich intermediátů., The dissertation thesis is focuses on the synthesis, characterization and biological activity of 2-hydroxy-N-(aryl) benzamides and their intermediates., Ústav organické chemie a technologie, Dokončená práce s úspěšnou obhajobou

Eukaryotic release factors 1 and 3, encoded by SUP45 and SUP35, respectively, in Saccharomyces cerevisiae, are required for translation termination. Recent studies have shown that, besides these two key factors, several genetic and epigenetic mechanisms modulate the efficiency of translation termination. These mechanisms, through modifying translation termination fidelity, were shown to affect various cellular processes, such as mRNA degradation, and in some cases could confer a beneficial phenotype to the cell. The most studied example of such a mechanism is [PSI+], the prion conformation of Sup35p, which can have pleiotropic effects on growth that vary among different yeast strains. However, genetic loci underlying such readthrough-dependent, background-specific phenotypes have yet to be identified. Here, we used sup35(C653R), a partial loss-of-function allele of the SUP35 previously shown to increase readthrough of stop codons and recapitulate some [PSI+]-dependent phenotypes, to study the genetic basis of phenotypes revealed by increased translational readthrough in two divergent yeast strains: BY4724 (a laboratory strain) and RM11_1a (a wine strain). We first identified growth conditions in which increased readthrough of stop codons by sup35(C653R) resulted in different growth responses between these two strains. We then used a recently developed linkage mapping technique, extreme QTL mapping (X-QTL), to identify readthrough-dependent loci for the observed growth differences. We further showed that variation in SKY1, an SR protein kinase, underlies a readthrough-dependent locus observed for growth on diamide and hydrogen peroxide. We found that the allelic state of SKY1 interacts with readthrough level and the genetic background to determine growth rate in these two conditions.

Eukaryotic release factors 1 and 3, encoded by SUP45 and SUP35, respectively, in Saccharomyces cerevisiae, are required for translation termination. Recent studies have shown that, besides these two key factors, several genetic and epigenetic mechanisms modulate the efficiency of translation termination. These mechanisms, through modifying translation termination fidelity, were shown to affect various cellular processes, such as mRNA degradation, and in some cases could confer a beneficial phenotype to the cell. The most studied example of such a mechanism is [PSI+], the prion conformation of Sup35p, which can have pleiotropic effects on growth that vary among different yeast strains. However, genetic loci underlying such readthrough-dependent, background-specific phenotypes have yet to be identified. Here, we used sup35(C653R), a partial loss-of-function allele of the SUP35 previously shown to increase readthrough of stop codons and recapitulate some [PSI+]-dependent phenotypes, to study the genetic basis of phenotypes revealed by increased translational readthrough in two divergent yeast strains: BY4724 (a laboratory strain) and RM11_1a (a wine strain). We first identified growth conditions in which increased readthrough of stop codons by sup35(C653R) resulted in different growth responses between these two strains. We then used a recently developed linkage mapping technique, extreme QTL mapping (X-QTL), to identify readthrough-dependent loci for the observed growth differences. We further showed that variation in SKY1, an SR protein kinase, underlies a readthrough-dependent locus observed for growth on diamide and hydrogen peroxide. We found that the allelic state of SKY1 interacts with readthrough level and the genetic background to determine growth rate in these two conditions.

Vitamin C synthesis in rat liver is enhanced by several xenobiotics, including aminopyrine and chloretone. The effect of these agents has been linked to induction of enzymes potentially involved in the formation of glucuronate, a precursor of vitamin C. Using isolated rat hepatocytes as a model, we show that a series of agents (aminopyrine, antipyrine, chloretone, clotrimazole, metyrapone, proadifen, and barbital) induced in a few minutes an up to 15-fold increase in the formation of glucuronate, which was best observed in the presence of sorbinil, an inhibitor of glucuronate reductase. They also caused an approximately 2-fold decrease in the concentration of UDP-glucuronate but little if any change in the concentration of UDP-glucose. Depletion of UDP-glucuronate with resorcinol or d-galactosamine markedly decreased the formation of glucuronate both in the presence and in the absence of aminopyrine, confirming the precursor-product relationship between UDP-glucuronate and free glucuronate. Most of the agents did not induce the formation of detectable amounts of glucuronides, indicating that the formation of glucuronate is not due to a glucuronidation-deglucuronidation cycle. With the exception of barbital (which inhibits glucuronate reductase), all of the above mentioned agents also caused an increase in the concentration of ascorbic acid. They had little effect on glutathione concentration, and their effect on glucuronate and vitamin C formation was not mimicked by glutathione-depleting agents such as diamide and buthionine sulfoximine. It is concluded that the stimulation of vitamin C synthesis exerted by some xenobiotics is mediated through a rapid increase in the conversion of UDP-glucuronate to glucuronate, which does not apparently involve a glucuronidation-deglucuronidation cycle.