Digitonin permeabilization of Saccharomyces cerevisiae cells for in situ enzyme assay

Targeting APEX2 to the mRNA encoding fatty acid synthase β in yeast identifies interacting proteins that control its abundance in the cell cycle

Profiling the repertoire of proteins associated with a given mRNA during the cell cycle is unstudied. Furthermore, it is easier to ask and answer what mRNAs a specific protein might bind to than the other way around. Here, we implemented an RNA-centric proximity labeling technology at different points in the cell cycle in highly synchronous yeast cultures. To understand how the abundance of FAS1, encoding fatty acid synthase, peaks late in the cell cycle, we identified proteins that interact with the FAS1 transcript in a cell cycle-dependent manner. We used dCas13d-APEX2 fusions to target FAS1 and label nearby proteins, which were then identified by mass spectrometry. The glycolytic enzyme Tdh3p, a known RNA-binding protein, interacted with the FAS1 mRNA, and it was necessary for the periodic abundance of Fas1p in the cell cycle. These results point to unexpected connections between major metabolic pathways. They also underscore the role of mRNA-protein interactions for gene expression during cell division.

TSPAN1 upregulates MMP2 to promote pancreatic cancer cell migration and invasion via PLCγ

Pancreatic cancer (PC), a malignancy of the digestive system, has one of the highest rates of metastasis and mortality. It is characterized by the detachment, migration, implantation and infiltration of tumor cells to form metastases or recurrent foci. Tetraspanin 1 (TSPAN1), a novel member of the TSPAN superfamily, is highly expressed in many types of cancer, including gastric, colon, liver and esophageal cancer. It has also been associated with lymph node metastasis, tumor recurrence and metastasis. However, the role of TSPAN1 in PC has not been fully elucidated. The aim of the present study was to determine the expression of TSPAN1 in human PC tissue samples and cell lines. Additionally, the functions of TSPAN1 in PC cell migration and invasion were assessed. The protein and gene expression of TSPAN1 was analyzed in clinical PC tissue samples and human PC cell lines (SW1990, BxPC3, Capan1 and PANC-1) via immunohistochemistry, reverse transcription-quantitative polymerase chain reaction and western blotting. The effect of TSPAN1 downregulation and overexpression in PC cells, via transfection with siRNA and pLNCX-TSPAN1-cDNA recombinant plasmid, respectively, on cell invasion and migration were assessed. Additionally, the mRNA expression of matrix metalloproteinase (MMP2) and MMP9 were determined. In clinical PC tissue samples, the expression of TSPAN1 was markedly increased when compared with normal pancreatic tissue samples. TSPAN1 was also highly expressed in PC cell lines compared with HPDE, a normal pancreatic cell line. Transfection with siRNA targeting TSPAN1 in PC cell lines significantly suppressed PC cell migration and invasion, and downregulated the expression of MMP2. However, there was no effect on MMP9. Consistently, PC cell migration and invasion together with MMP2 mRNA expression were markedly increased following TSPAN1 ectopic overexpression. The present study utilized small interfering RNAs (siRNA) targeted to phospholipase Cγ (PLCγ) to demonstrate that TSPAN1 siRNA suppressed PC cell migration and invasion, and MMP2 mRNA expression by blocking the translocation and phosphorylation of PLCγ. The results of the present study revealed that TSPAN1 has an important function in human PC cell migration and invasion by modulating MMP2 expression via PLCγ. Thus, the results indicate that the silencing of TSPAN1 may be a potential therapeutic target for the treatment of PC.

Influence of boric acid on energy metabolism and stress tolerance of Candida albicans

Boron presents at physiological pH in the form of boric acid (BA), a molecule that has both positive and negative effects on biological processes. In medicine, BA is used as a topical treatment for vaginal yeast infections by Candida species because of its well-documented but poorly understood effect on inhibition of growth in general and of invasive, hyphal growth in particular. The present study examines the influence of BA on carbohydrate energy metabolism of this common human pathogen. Starting from previous findings about an inhibition of key NAD-dependent enzymes by BA in vitro, we confirmed that such an inhibition occurs in permeabilized C. albicans cells. Cultures growing even with moderate concentrations of BA experience mitochondrial failure, increase ethanol production from glucose and decrease the deposition of carbohydrate stores in the form of glycogen. Cells growing on the non-fermentable, FAD-generating carbon source lactate have a higher BA tolerance, which suggests that the toxicity of BA is rooted in an inhibition of NAD-dependent reactions and the increased production of ethanol. Boric acid exposure sensitizes C. albicans selectively to the toxic effects of ethanol. This additive effect suggests that the endogenously produced ethanol increases the load on ethanol resistance mechanisms. Lastly, combination studies showed no interactions of BA with common antifungal drugs, meaning that addition of BA to topical formulations can provide an additive antifungal effect regardless of the chosen active ingredient.

α-1,3-Fucosyltransferase-VII siRNA inhibits the expression of SLex and hepatocarcinoma cell proliferation

The increased expression of sialyl-Lewisx (SLe^x) epitope on the surface of tumor cells has been known for decades. However, genetic manipulation of the expression of SLe^x and the role of SLe^x in cancer cell proliferation remains to be fully elucidated. The present study suggested that the monoclonal antibody of SLe^x (KM93) significantly inhibited the proliferation of human hepatocarcinoma (HCC) cells. The expression levels of three sialyl-Lewis oligosaccharide antigens, SLe^x, SLe^a and dimeric SLe^x (SDLe^x), were determined on the cell surface of the MHCC97 human HCC cell line. The expression of SLe^x was markedly higher in MHCC97 cells than in normal liver cells. The expression of SDLe^x was also relatively high, however, no significant difference was observed between normal liver cells and HCC cells. The expression of SLe^a was only detected in trace quantities. Fucosyltransferase (FUT) is the key enzyme of the fucosylation step in the biosynthesis of sialyl-Lewis oligosaccharide antigens. Therefore, the present study investigated the expression of FUTs. It was found that the mRNA and protein expression levels of FUT7 were high in the MHCC97 HCC cell line compared with levels in normal liver cells. FUT6 was also expressed at a high level, although the difference was not statistically significant between MHCC97 cells and normal liver cells. No expression of FUT3 was detected. The results were consistent with the change insialyl-Lewis antigens. The effects of FUT7 small interfering (si)RNA transfection on the expression of FUT7, expression of SLe^x and MHCC97 cell proliferation were also examined. Following FUT7 siRNA transfection, the expression of FUT7 was markedly downregulated, as determined by western blot and reverse transcription-quantitative polymerase chain reaction methods. The results from flow cytometry showed that the synthesis of SLe^x was also inhibited, which was consistent with the downregulated expression of FUT7. MHCC97 cell proliferation was also significantly inhibited following FUT7 siRNA transfection, which was correlated with suppression of the S-phase in cell cycle progression. By using inhibitors of various signaling pathways, it was found that the knockdown of FUT7 inhibited the activation of phospholipase Cγ (PLCγ) by inhibiting the translocation and phosphorylation of PLCγ. In conclusion, the results suggested that FUT7 has animportant functional role in human HCC cell proliferation by controlling cell cycle progression via the PLCγ/extracellular signal-regulated kinase signaling pathway. The inhibition of SLe^x and FUT7 siRNA transfection may provide a novel therapeutic methodology to treat tumors that express SLe^x glycoconjugates.

Enantioselective Synthesis of Vicinal (R,R)-Diols by Saccharomyces cerevisiae Butanediol Dehydrogenase

Butanediol dehydrogenase (Bdh1p) from Saccharomyces cerevisiae belongs to the superfamily of the medium-chain dehydrogenases and reductases and converts reversibly R-acetoin and S-acetoin to (2R,3R)-2,3-butanediol and meso-2,3-butanediol, respectively. It is specific for NAD(H) as a coenzyme, and it is the main enzyme involved in the last metabolic step leading to (2R,3R)-2,3-butanediol in yeast. In this study, we have used the activity of Bdh1p in different forms-purified enzyme, yeast extracts, permeabilized yeast cells, and as a fusion protein (with yeast formate dehydrogenase, Fdh1p)-to transform several vicinal diketones to the corresponding diols. We have also developed a new variant of the delitto perfetto methodology to place BDH1 under the control of the GAL1 promoter, resulting in a yeast strain that overexpresses butanediol dehydrogenase and formate dehydrogenase activities in the presence of galactose and regenerates NADH in the presence of formate. While the use of purified Bdh1p allows the synthesis of enantiopure (2R,3R)-2,3-butanediol, (2R,3R)-2,3-pentanediol, (2R,3R)-2,3-hexanediol, and (3R,4R)-3,4-hexanediol, the use of the engineered strain (as an extract or as permeabilized cells) yields mixtures of the diols. The production of pure diol stereoisomers has also been achieved by means of a chimeric fusion protein combining Fdh1p and Bdh1p. Finally, we have determined the selectivity of Bdh1p toward the oxidation/reduction of the hydroxyl/ketone groups from (2R,3R)-2,3-pentanediol/2,3-pentanedione and (2R,3R)-2,3-hexanediol/2,3-hexanedione. In conclusion, Bdh1p is an enzyme with biotechnological interest that can be used to synthesize chiral building blocks. A scheme of the favored pathway with the corresponding intermediates is proposed for the Bdh1p reaction.

Physiological tests for yeast brewery cells immobilized on modified chamotte carrier

In this study yeast cell physiological activity was assessed on the basis of the in situ activity of two important enzymes, succinate dehydrogenase and pyruvate decarboxylase. FUN1 dye bioconversion and cellular ATP content were also taken as important indicators of yeast cell activity. The study was conducted on six brewing yeast strains, which were either free cells or immobilized on a chamotte carrier. The experimental data obtained indicate clearly that, in most cases, the immobilized cells showed lower enzyme activity than free cells from analogous cultures. Pyruvate decarboxylase activity in immobilized cells was higher than in planktonic cell populations only in the case of the Saccharomyces pastorianus 680 strain. However, in a comparative assessment of the fermentation process, conducted with the use of free and immobilized cells, much more favorable dynamics and carbon dioxide productivity were observed in immobilized cells, especially in the case of brewing lager yeast strains. This may explain the higher total cell density per volume unit of the fermented medium and the improved resistance of immobilized cells to environmental changes.

Subcellular localization of the fatty acyl reductase involved in pheromone biosynthesis in the tobacco budworm, Heliothis virescens (Noctuidae: Lepidoptera)

Sex pheromone components are produced in specialized glands of female moths via well-characterized biosynthetic pathways, where a Fatty Acyl Reductase (FAR) is often essential for producing the specific ratio of the different pheromone components. The subcellular localization and membrane topology of FARs is important for understanding how pheromones are synthesized and exported to the exterior for release. We investigated the subcellular localization of HvFAR from the noctuid moth Heliothis virescens by producing recombinant fusion proteins with green fluorescent protein (GFP) in yeast. A C-terminally tagged construct was localized to the endoplasmic reticulum (ER) and retained full reductive activity on a broad range of saturated and unsaturated fatty acyl precursors. In contrast, an N-terminally-tagged construct was poorly expressed in the cytoplasm and was not enzymatically active, indicating that HvFAR requires a free N-terminal for both proper targeting and catalytic activity. A series of truncations of the N-and C-termini of HvFAR was conducted based on in silico-predicted hydrophobic domains and transmembrane regions. The N-terminally truncated protein was found in the cytoplasm and did not retain activity, emphasizing the importance of the N-terminal for FAR function. In addition, the orientation in the membrane of the C-terminus-tagged HvFAR-GFP construct was analyzed using a fluorescence protease protection (FPP) assay, implying that the C-terminal of HvFAR is orientated towards the cytoplasm. These results, together with previous data on the localization of desaturases, confirm the importance of the ER as a subcellular site of pheromone production.

Eukaryotic metabolism: measuring compartment fluxes

Metabolic compartmentation represents a major characteristic of eukaryotic cells. The analysis of compartmented metabolic networks is complicated by separation and parallelization of pathways, intracellular transport, and the need for regulatory systems to mediate communication between interdependent compartments. Metabolic flux analysis (MFA) has the potential to reveal compartmented metabolic events, although it is a challenging task requiring demanding experimental techniques and sophisticated modeling. At present no ready-made solution can be provided to cope with the complexity of compartmented metabolic networks, but new powerful tools are emerging. This review gives an overview of different strategies to approach this issue, focusing on different MFA methods and highlighting the additional information that should be included to improve the outcome of an experiment and associate estimation procedures.

A genetic analysis of nitrosative stress

Nitrosative stress is induced by pathophysiological levels of nitric oxide (NO) and S-nitrosothiols (e.g., S-nitrosoglutathione, GSNO) and arises, at least in significant part, from the nitrosylation of critical protein Cys thiols (S-nitrosylation) and metallocofactors. However, the mechanisms by which NO and GSNO mediate nitrosative stress are not well understood. Using yeast Saccharomyces cerevisiae strains lacking NO- and/or GSNO-consuming enzymes (flavohemoglobin and GSNO reductase, respectively), we measured the individual and combined effects of NO and GSNO on both cell growth and the formation of protein-bound NO species. Our results suggest an intracellular equilibrium between NO and GSNO, dependent in part on cell-catalyzed release of NO from GSNO (i.e., "SNO-lyase" activity). However, whereas NO induces multiple types of protein-based modifications, levels of which correlate with inhibition of cell growth, GSNO mainly affects protein S-nitrosylation, and the relationship between S-nitrosylation and nitrosative stress is more complex. These data support the idea of multiple classes of protein-SNO, likely reflected in divergent routes of synthesis and degradation. Indeed, a significant fraction of protein S-nitrosylation by NO occurs in the absence of O(2), which is commonly assumed to drive this reaction but instead is apparently dependent in substantial part upon protein-bound transition metals. Additionally, our findings suggest that nitrosative stress is mediated principally via the S-nitrosylation of a subset of protein targets, which include protein SNOs that are stable to cellular glutathione (and thus are not metabolized by GSNO reductase). Collectively, these results provide new evidence for the mechanisms through which NO and GSNO mediate nitrosative stress as well as the cellular pathways of protein S-nitrosylation and denitrosylation involving metalloproteins, SNO lyase(s) and GSNO reductase.

Measuring intracellular enzyme concentrations: Assessing the effect of oxidative stress on the amount of glyoxalase I

Enzymology is one of the fundamental areas of biochemistry and involves the study of the structure, kinetics, and regulation of enzyme activity. Research in this area is often conducted with purified enzymes and extrapolated to in vivo conditions. The specificity constant, k(S) , is the ratio between k(cat) (the catalytic constant) and K(m) (Michaelis-Menten constant), and expresses the efficiency of an enzyme as a catalyst. This parameter is usually determined for purified enzymes, and in this work, we propose a classroom experiment for its determination in situ, in permeabilized yeast cells, based on a method of external enzyme addition, which was previously reported. Under these conditions, which resemble the in vivo state, enzyme concentrations and protein interactions are preserved. The students are presented with a novel approach in enzymology, based on the titration methods that allow the measurement of the enzyme amount, and thus the k(cat) and k(S) . The method will also be used to investigate the effect of exposure to oxidative stress conditions on yeast glyoxalase I.

Extracellular methylglyoxal toxicity in Saccharomyces cerevisiae: role of glucose and phosphate ions

AIM

The purpose of this study was to investigate the behaviour of Saccharomyces cerevisiae in response to extracellular methylglyoxal.

METHODS AND RESULTS

Cell survival to methylglyoxal and the importance of phosphates was investigated. The role of methylglyoxal detoxification systems and methylglyoxal-derived protein glycation were studied and the relation to cell survival or death was evaluated. Extracellular methylglyoxal decreased cell viability, and the presence of phosphate enhanced this effect. D-glucose seems to exert a protective effect towards this toxicity. Methylglyoxal-induced cell death was not apoptotic and was not related to intracellular glycation processes. The glyoxalases and aldose reductase were important in methylglyoxal detoxification. Mutants lacking glyoxalase I and II showed increased sensitivity to methylglyoxal, while strains overexpressing these genes had increased resistance.

CONCLUSIONS

Extracellular methylglyoxal induced non-apoptotic cell death, being unrelated to glycation. Inactivation of methylglyoxal-detoxifying enzymes by phosphate is one probable cause. Phosphate and D-glucose may also act through their complex involvement in stress response mechanisms.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings contribute to elucidate the mechanisms of cell toxicity by methylglyoxal. This information could be useful to on-going studies using yeast as a eukaryotic cell model to investigate methylglyoxal-derived glycation and its role in neurodegenerative diseases.

Addressing membrane protein topology using the fluorescence protease protection (FPP) assay

Determining a protein's correct topological distribution within the cell is essential for understanding the proper functioning of many proteins. Here, we describe a fluorescence-based technique, termed FPP for fluorescence protease protection, to determine protein topology in living cells. The FPP assay uses the restricted proteolytic digestibility of green fluorescent protein-tagged membrane proteins to reveal their intramembrane orientation. Membrane protein topology can be assessed using this technique for proteins residing in organelles as diverse as the Golgi apparatus, the endoplasmic reticulum (ER), peroxisomes, mitochondria, and autophagosomes. To illustrate the technique, we describe its use for deciphering the topology of a membrane protein in the ER.

Yeast protein glycation in vivo by methylglyoxal. Molecular modification of glycolytic enzymes and heat shock proteins

Protein glycation by methylglyoxal is a nonenzymatic post-translational modification whereby arginine and lysine side chains form a chemically heterogeneous group of advanced glycation end-products. Methylglyoxal-derived advanced glycation end-products are involved in pathologies such as diabetes and neurodegenerative diseases of the amyloid type. As methylglyoxal is produced nonenzymatically from dihydroxyacetone phosphate and d-glyceraldehyde 3-phosphate during glycolysis, its formation occurs in all living cells. Understanding methylglyoxal glycation in model systems will provide important clues regarding glycation prevention in higher organisms in the context of widespread human diseases. Using Saccharomyces cerevisiae cells with different glycation phenotypes and MALDI-TOF peptide mass fingerprints, we identified enolase 2 as the primary methylglyoxal glycation target in yeast. Two other glycolytic enzymes are also glycated, aldolase and phosphoglycerate mutase. Despite enolase's activity loss, in a glycation-dependent way, glycolytic flux and glycerol production remained unchanged. None of these enzymes has any effect on glycolytic flux, as evaluated by sensitivity analysis, showing that yeast glycolysis is a very robust metabolic pathway. Three heat shock proteins are also glycated, Hsp71/72 and Hsp26. For all glycated proteins, the nature and molecular location of some advanced glycation end-products were determined by MALDI-TOF. Yeast cells experienced selective pressure towards efficient use of d-glucose, with high methylglyoxal formation as a side effect. Glycation is a fact of life for these cells, and some glycolytic enzymes could be deployed to contain methylglyoxal that evades its enzymatic catabolism. Heat shock proteins may be involved in proteolytic processing (Hsp71/72) or protein salvaging (Hsp26).

Fluorescence protease protection of GFP chimeras to reveal protein topology and subcellular localization

Understanding the cell biology of many proteins requires knowledge of their in vivo topological distribution. Here we describe a new fluorescence-based technique, fluorescence protease protection (FPP), for investigating the topology of proteins and for localizing protein subpopulations within the complex environment of the living cell. In the FPP assay, adapted from biochemical protease protection assays, GFP fusion proteins are used as noninvasive tools to obtain details of protein topology and localization within living cells in a rapid and straightforward manner. To demonstrate the broad applicability of FPP, we used the technique to define the topology of proteins localized to a wide range of organelles including the endoplasmic reticulum (ER), Golgi apparatus, mitochondria, peroxisomes and autophagosomes. The success of the FPP assay in characterizing the topology of the tested proteins within their appropriate compartments suggests this technique has wide applicability in studying protein topology and localization within the cell.

ChIC and ChEC; genomic mapping of chromatin proteins

To map the genomic interaction sites of chromatin proteins, two related methods were developed and experimentally explored in Saccharomyces cerevisiae. The ChIC method (chromatin immunocleavage) consists of tethering a fusion protein (pA-MN) consisting of micrococcal nuclease (MN) and staphylococcal protein A to specifically bound antibodies. The nuclease is kept inactive during the tethering process (no Ca2+). The ChEC method (chromatin endogenous cleavage) consists of expressing fusion proteins in vivo, where MN is C-terminally fused to the proteins of interest. The specifically tethered nucleases are activated with Ca2+ ions to locally introduce double-stranded DNA breaks. We demonstrate that ChIC and ChEC map proteins with a 100-200 bp resolution and excellent specificity. One version of the method is applicable to formaldehyde-fixed nuclei, another to native cells with comparable results. Among various model experiments, these methods were used to address the conformation of yeast telomeres.

The total quasi-steady-state approximation is valid for reversible enzyme kinetics

The Briggs-Haldane approximation of the irreversible Michaelis-Menten scheme of enzyme kinetics is cited in virtually every biochemistry textbook and is widely considered the classic example of a quasi-steady-state approximation. Though of similar importance, the reversible Michaelis-Menten scheme is not as well characterized. This is a serious limitation since even enzymatic reactions that go to completion may be reversible. The current work derives a total quasi-steady-state approximation (tQSSA) for the reversible Michaelis-Menten and delineates its validity domain. The tQSSA allows the derivation of uniformly valid approximations for the limit of low enzyme concentrations, ET<<ST+KM, and under certain more restrictive conditions also for high enzyme concentrations such that ST<<ET+KM. Using these simple analytical approximations, a sequential experimental-theoretical method is suggested for unambiguously estimating all the kinetic parameters of the reversible Michaelis-Menten scheme.

Feasibility of measuring ferricyanide reduction by yeasts to estimate their activity during alcoholic fermentation in wine-making conditions

We assessed the feasibility of measuring the extracellular reduction of ferricyanide in the presence of an intermediate carrier (menadione) as a means of estimating the activity of yeasts during alcoholic fermentation. A spectrophotometric and a potentiometric approach were used. Comparison of specific reductase activity and gas production rate during the stationary phase indicated that measuring the menadione-catalyzed reduction of ferricyanide provides a good estimate of the total activity of the yeast cells in a fermenting must. The response observed following the addition of an electron acceptor (acetaldehyde) confirmed that the reductase activity of menadione is dependent on the availability of NADH. The stability of menadione in the fermentation medium, as assessed by the potentiometric method, suggested that electrochemical reoxidation of the ferrocyanide can act as a substitute for the addition of an electron acceptor when studying the redox regulation of fermenting yeasts.

In situ kinetic analysis of glyoxalase I and glyoxalase II in Saccharomyces cerevisiae

The kinetics of glyoxalase I [(R)-S-lactoylglutathione methylglyoxal-lyase; EC 4.4.1.5] and glyoxalase II (S-2-hydroxyacylglutathione hydrolase; EC 3.1.2.6) from Saccharomyces cerevisiae was studied in situ, in digitonin permeabilized cells, using two different approaches: initial rate analysis and progress curves analysis. Initial rate analysis was performed by hyperbolic regression of initial rates using the program HYPERFIT. Glyoxalase I exhibited saturation kinetics on 0.05-2.5 mM hemithioacetal concentration range, with kinetic parameters Km 0.53 +/- 0.07 mM and V (3.18 +/- 0.16) x 10(-2) mM.min(-1). Glyoxalase II also showed saturation kinetics in the SD-lactoylglutathione concentration range of 0.15-3 mM and Km 0.32 +/- 0.13 mM and V (1.03 +/- 0.10) x 10(-3) mM.min(-1) were obtained. The kinetic parameters of both enzymes were also estimated by nonlinear regression of progress curves using the raw absorbance data and integrated differential rate equations with the program GEPASI. Several optimization methods were used to minimize the sum of squares of residuals. The best parameter fit for the glyoxalase I reaction was obtained with a single curve analysis, using the irreversible Michaelis-Menten model. The kinetic parameters obtained, Km 0.62 +/- 0.18 mM and V (2.86 +/- 0.01) x 10(-2) mM.min(-1), were in agreement with those obtained by initial rate analysis. The results obtained for glyoxalase II, using either the irreversible Michaelis-Menten model or a phenomenological reversible hyperbolic model, showed a high correlation of residuals with time and/or high values of standard deviation associated with Km. The possible causes for the discrepancy between data obtained from initial rate analysis and progress curve analysis, for glyoxalase II, are discussed.

In situ analysis of methylglyoxal metabolism in Saccharomyces cerevisiae

Methylglyoxal metabolism was studied during Saccharomyces cerevisiae grown with D-glucose as the sole carbon and energy source. Using for the first time a specific assay for methylglyoxal in yeast, metabolic fluxes of its formation and D-lactate production were determined. D-Glucose consumption and ethanol production were determined during growth. Metabolic fluxes were also determined in situ, at the glycolytic triose phosphate levels and glyoxalase pathway. Maximum fluxes of ethanol production and glucose consumption correspond to maxima of methylglyoxal and D-lactate formation fluxes during growth. Methylglyoxal formation is quantitatively related to glycolysis, representing 0.3% of the total glycolytic flux in S. cerevisiae.

Catalases and thioredoxin peroxidase protect Saccharomyces cerevisiae against Ca(2+)-induced mitochondrial membrane permeabilization and cell death

The involvement of reactive oxygen species in Ca(2+)-induced mitochondrial membrane permeabilization and cell viability was studied using yeast cells in which the thioredoxin peroxidase (TPx) gene was disrupted and/or catalase was inhibited by 3-amino-1,2, 4-triazole (ATZ) treatment. Wild-type Saccharomyces cerevisiae cells were very resistant to Ca(2+) and inorganic phosphate or t-butyl hydroperoxide-induced mitochondrial membrane permeabilization, but suffered an immediate decrease in mitochondrial membrane potential when treated with Ca(2+) and the dithiol binding reagent phenylarsine oxide. In contrast, S. cerevisiae spheroblasts lacking the TPx gene and/or treated with ATZ suffered a decrease in mitochondrial membrane potential, generated higher amounts of hydrogen peroxide and had decreased viability under these conditions. In all cases, the decrease in mitochondrial membrane potential could be inhibited by ethylene glycol-bis(beta-aminoethyl ether) N,N, N',N'-tetraacetic acid, dithiothreitol or ADP, but not by cyclosporin A. We conclude that TPx and catalase act together, maintaining cell viability and protecting S. cerevisiae mitochondria against Ca(2+)-promoted membrane permeabilization, which presents similar characteristics to mammalian permeability transition.

Glyoxalase II in Saccharomyces cerevisiae: in situ kinetics using the 5,5'-dithiobis(2-nitrobenzoic acid) assay

The determination of glyoxalase II (S-(2-hydroxyacyl)glutathione hydrolase, EC 3.1.2.6) activity is usually accomplished by monitoring the decrease of absorbance at 240 nm due to the hydrolysis of S-d-lactoylglutathione. However, it was not possible, using this assay, to detect any enzyme activity in situ, in Saccharomyces cerevisiae permeabilized cells. Glyoxalase II activity was then determined by following the formation of GSH at 412 nm using 5,5'-dithiobis(2-nitrobenzoic acid). Using this method we characterized the kinetics of glyoxalase II in situ using S-d-lactoylglutathione as substrate and compared the results with those obtained for cell-free extracts. The specific activity was found to be (4.08 +/- 0.12) x 10(-2) micromol min-1 mg-1 in permeabilized cells and (3.90 +/- 0.04) x 10(-2) micromol min1 mg-1 in cell-free extracts. Kinetic parameters were Km 0.36 +/- 0.09 mM and V (7.65 +/- 0.59) x 10(-4) mM min-1 for permeabilized cells and Km 0.15 +/- 0.10 mM and V (7.23 +/- 1.04) x 10(-4) mM min-1 for cell-free extracts. d-Lactate concentration was also determined and increased in a linear way with permeabilized cell concentration. gamma-Glutamyl transferase (EC 2.3.2.2), which also accepts S-d-lactoylglutathione as substrate and hence could interfere with glyoxalase II assays, was found to be absent in Saccharomyces cerevisiae permeabilized cells.