Recent evidence has revealed the occurrence of an apoptotic phenotype in

The free radical theory of aging posits oxidative damage to macromolecules as a primary determinant of lifespan. Recent studies challenge this theory by demonstrating that in some cases, longevity is enhanced by inactivation of oxidative stress defenses or is correlated with increased, rather than decreased reactive oxygen species and oxidative damage. Here we show that, in Saccharomyces cerevisiae, caloric restriction or inactivation of catalases extends chronological lifespan by inducing elevated levels of the reactive oxygen species hydrogen peroxide, which activate superoxide dismutases that inhibit the accumulation of superoxide anions. Increased hydrogen peroxide in catalase-deficient cells extends chronological lifespan despite parallel increases in oxidative damage. These findings establish a role for hormesis effects of hydrogen peroxide in promoting longevity that have broad implications for understanding aging and age-related diseases.aging | hydrogen peroxide | hormesis | antioxidant enzymes | oxidative damage T he longstanding free radical theory has guided investigations into the causes and consequences of aging for more than 50 y (1). However, the results of a number of recent studies have failed to provide support for the free radical theory or suggest that this theory is at best incomplete (2). Studies of naked mole rats, for example, demonstrated that this extremely long-lived rodent exhibits high levels of oxidative damage compared with mice or rats, whose lifespans are ≈1/10 that of naked mole rats (3). In addition, caloric restriction (CR), which extends the lifespans of a variety of eukaryotic organisms, promotes longevity in Caenorhabditis elegans by a mechanism that involves increased oxidative stress (4). In fact, in contrast to the destructive effects of reactive oxygen species (ROS), recent evidence indicates that in mammals, hydrogen peroxide (H 2 O 2 ) and other forms of ROS function as essential secondary messengers in the regulation of a variety of physiological processes (reviewed in ref. 5). For example, H 2 O 2 activates prosurvival signaling pathways mediated by p53, NF-κB, AP-1, and other molecules (6). Furthermore, increases in the intracellular steady-state production of H 2 O 2 by SOD2 overexpression can block the activation of cellular processes required for programmed cell death (7). However, a causal relationship between CR and effects on oxidative stress has been difficult to establish.To better understand how CR impacts oxidative stress and longevity in the model organism Saccharomyces cerevisiae, in this study we examined intracellular levels of H 2 O 2 and superoxide anions (O 2 − ), which are two forms of ROS implicated in aging in all eukaryotes, under CR and other conditions. Our findings indicate that CR or inactivation of catalases extends chronological lifespan (CLS) by inducing elevated levels of H 2 O 2 , which activate superoxide dismutases that inhibit the accumulation of O 2 − . These findings establish a role for hormesis effects of H 2 O 2 in promoting l...

Cells of the yeast Sacchammyces cerevisiae IGC 4072 grown in medium with acetic acid produced a mediated transport system for acetic acid that behaved as an electroneutral proton symport for the anionic form of the acid. The system could transport propionate and formate but not lactate and pyruvate. Uptake of labelled lactic acid was negligible, no mediated transport system activity for this acid being found. The acetate transporter was also found in cells grown in lactic acid or ethanol media, suggesting that the carrier did not require the presence of an external inducer. When cells were grown in lactic acid medium, uptake of labelled acetic acid, a t pH 5.0, was biphasic and consistent with the presence of two distinct transport modes for the acid. One of these components corresponded to the acetatelproton symport, and the higher affinity system corresponded to a more general monocarboxylate carrier that could also transport lactate, pyruvate and propionate. Both systems were subject to repression by glucose, fructose, sucrose, maltose or galactose. In glucose-repressed cells, the undissociated form of the acids appeared to be the only one that could cross the plasma membrane, a diffusion mechanism being involved in the acid uptake. Under these growth conditions and when the extracellular pH was lower than that of the cytosol, accumulation of the acid could also be observed, it being a function of the ApH.

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Although acetic acid has been shown to induce apoptosis in yeast, the exact apoptotic mechanisms remain unknown. Here, we studied the effects of acetic acid treatment on yeast cells by 2-DE, revealing alterations in the levels of proteins directly or indirectly linked with the target of rapamycin (TOR) pathway: amino-acid biosynthesis, transcription/translation machinery, carbohydrate metabolism, nucleotide biosynthesis, stress response, protein turnover and cell cycle. The increased levels of proteins involved in amino-acid biosynthesis presented a counteracting response to a severe intracellular amino-acid starvation induced by acetic acid. Deletion of GCN4 and GCN2 encoding key players of general amino-acid control (GAAC) system caused a higher resistance to acetic acid indicating an involvement of Gcn4p/Gcn2p in the apoptotic signaling. Involvement of the TOR pathway in acetic acid-induced apoptosis was also reflected by the higher survival rates associated to a terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-negative phenotype and lower reactive oxygen species levels of Deltator1 cells. In addition, deletion mutants for several downstream mediators of the TOR pathway revealed that apoptotic signaling involves the phosphatases Pph21p and Pph22p but not Sit4p. Altogether, our results indicate that GAAC and TOR pathways (Tor1p) are involved in the signaling of acetic acid-induced apoptosis.

Aims: To study the effects of assimilable nitrogen concentration on growth profile and on fermentation kinetics of Saccharomyces cerevisiae. Methods and Results: Saccharomyces cerevisiae was grown in batch in a defined medium with glucose (200 g l )1 )as the only carbon and energy source, and nitrogen supplied as ammonium sulphate or phosphate forms under different concentrations. The initial nitrogen concentration in the media had no effect on specific growth rates of the yeast strain PYCC 4072. However, fermentation rate and the time required for completion of the alcoholic fermentation were strongly dependent on nitrogen availability. At the stationary phase, the addition of ammonium was effective in increasing cell population, fermentation rate and ethanol. Conclusions:The yeast strain required a minimum of 267 mg N l )1 to attain complete dryness of media, within the time considered for the experiments. Lower levels were enough to support growth, although leading to sluggish or stuck fermentation. Significance and Impact of the Study: The findings reported here contribute to elucidate the role of nitrogen on growth and fermentation performance of wine yeast. This information might be useful to the wine industry where excessive addition of nitrogen to prevent sluggish or stuck fermentation might have a negative impact on wine stability and quality.

Nitric oxide (NO) is a small molecule with distinct roles in diverse physiological functions in biological systems, among them the control of the apoptotic signalling cascade. By combining proteomic, genetic and biochemical approaches we demonstrate that NO and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) are crucial mediators of yeast apoptosis. Using indirect methodologies and a NO-selective electrode, we present results showing that H2O2-induced apoptotic cells synthesize NO that is associated to a nitric oxide synthase (NOS)-like activity as demonstrated by the use of a classical NOS kit assay. Additionally, our results show that yeast GAPDH is a target of extensive proteolysis upon H2O2-induced apoptosis and undergoes S-nitrosation. Blockage of NO synthesis with Nω-nitro-L-arginine methyl ester leads to a decrease of GAPDH S-nitrosation and of intracellular reactive oxygen species (ROS) accumulation, increasing survival. These results indicate that NO signalling and GAPDH S-nitrosation are linked with H2O2-induced apoptotic cell death. Evidence is presented showing that NO and GAPDH S-nitrosation also mediate cell death during chronological life span pointing to a physiological role of NO in yeast apoptosis.

Zygosaccharomyces bailii ISA 1307 displays biphasic growth in a medium containing a mixture of glucose (0*5%, whr) and acetic acid (05Y0, whr), pH 5 9 and 39. In cells harvested during the first growth phase, no activity of a mediated acetic acid transport system was found. Incubation of these cells in phosphate buffer with cycloheximide for 1 h restored activity of an acetic acid carrier which behaved as the one present in glucose-grown cells. These results indicated that the acetic acid carrier is probably present in cells from the first growth phase of the mixed medium but its activity was affected by the presence of acetic acid in the culture medium. In glucose-grown cells, after incubation in phosphate buffer with glucose and acetic acid, the activity of the acetic acid carrier decreased significantly with increased acid concentration in the incubation buffer. A t acid concentrations above 1 6 7 mM, no significant carrier activity was detectable. Furthermore, the intracellular acid concentration increased with the extracellular one and was inversely correlated with the activity of the acetic acid carrier, suggesting the involvement of a feedback inhibition mechanism in the regulation of the carrier. During biphasic growth, the first phase corresponded to a simultaneous consumption of glucose and acetic acid, and the second to the utilization of the remaining acid. The enzyme acetyl-CoA synthetase was active in both growth phases, even in the presence of glucose. Activity of isocitrate lyase and phosphoenolpyruvate carboxykinase was found only in acetic-acidgrown cells. Thus it appears that both membrane transport and acetyl-CoA synthetase and their regulation are important for 2. bailii to metabolize acetic acid in the presence of glucose. This fact correlates with the high resistance of this yeast to environments with mixtures of sugars and acetic acid such as those often present during wine fermentation.