Micromolar HgCl2 concentrations transitorily duplicate the ATP level in Saccharomyces cerevisiae cells

Insights into ferulic acid detoxification mechanism by using a novel adsorbent, AEPA250: The microinteraction of ferulic acid with AEPA250 and Saccharomyces cerevisiae

In this study, a novel adsorbent, Air Environment-prepared Adsorbent at 250 ℃ (AEPA₂₅₀), was used to detoxify the main fermentation inhibitor (ferulic acid) present in the alkali-pretreated hydrolysate. AEPA₂₅₀ reduced the effective concentration of ferulic acid by its adsorption, thereby decreasing the possible interaction of ferulic acid with Saccharomyces cerevisiae. The results indicated that AEPA₂₅₀ functionalized with hydroxyl, carboxyl, and amino groups under acidic conditions with higher binding energies (-45.667, -27.046, and -11.008 kcal mol^-1, respectively) and electronic cloud overlap and shorter bond distances (1.015, 1.010, and 2.094 Å, respectively) than those under the other pH conditions. These differences revealed that the electrostatic interaction dominated ferulic acid adsorption on AEPA₂₅₀. Additionally, under acidic conditions and for carboxyl group functionalized AEPA₂₅₀, energy band gap values of Eg1 were higher than those of Eg2, indicating that ferulic acid provided the π-electrons for the π-π electron donor-acceptor interactions with AEPA₂₅₀. Furthermore, ferulic acid detoxification after AEPA₂₅₀ adsorption caused the regulation of YDR316W-B and YPR137C-B genes of S. cerevisiae. These results might contribute to the development of other more efficient adsorbents and pretreatment methods and allow yeast engineering for improving the scale-up and self-sufficient production of bioethanol in the future.

Phenotypic consequences of purine nucleotide imbalance in Saccharomyces cerevisiae

Coordinating homeostasis of multiple metabolites is a major task for living organisms, and complex interconversion pathways contribute to achieving the proper balance of metabolites. AMP deaminase (AMPD) is such an interconversion enzyme that allows IMP synthesis from AMP. In this article, we show that, under specific conditions, lack of AMPD activity impairs growth. Under these conditions, we found that the intracellular guanylic nucleotide pool was severely affected. In vivo studies of two AMPD homologs, Yjl070p and Ybr284p, indicate that these proteins have no detectable AMP, adenosine, or adenine deaminase activity; we show that overexpression of YJL070c instead mimics a loss of AMPD function. Expression of the yeast transcriptome was monitored in a AMPD-deficient mutant in a strain overexpressing YJL070c and in cells treated with the immunosuppressive drug mycophenolic acid, three conditions that lead to severe depletion of the guanylic nucleotide pool. These three conditions resulted in the up- or downregulation of multiple transcripts, 244 of which are common to at least two conditions and 71 to all three conditions. These transcriptome results, combined with specific mutant analysis, point to threonine metabolism as exquisitely sensitive to the purine nucleotide balance.

Cell death and cytotoxic effects in YAC-1 lymphoma cells following exposure to various forms of mercury

The effects of 1 min-4 h exposures to four Hg compounds (mercuric chloride [HgCl2], methyl mercuric chloride [CH3HgCl], p-chloromercuribenzoate [p-CMB] and thimerosal [TMS; ethylmercurithiosalicylate]) on cell death, microtubules, actin, CD3 receptor expression, protein tyrosine phosphorylation (PTyr-P) and intracellular calcium ([Ca2+]i) levels were investigated in YAC-1 lymphoma cells using flow cytometry. YOPRO-1 (YP) and propidium iodide (PI) dye uptake indicated all forms of Hg tested were toxic at concentrations ranging from 25.8-48.4 microM, with two distinct patterns of effects. Early apoptosis was prolonged for CH3HgCl- and TMS-treated cells, with more than 50% remaining YP+/PI- after 4h. Both CH3HgCl and TMS induced complete loss of beta-tubulin fluorescence, indicative of microtubule depolymerization and inhibition of tubulin synthesis and/or beta-tubulin degradation, while F-actin fluorescence diminished to a lesser degree and only after loss beta-tubulin. CH3HgCl and TMS induced an almost immediate two-fold increase in CD3 fluorescence, with levels returning to baseline within minutes. With continued exposure, CD3 fluorescence was reduced to approximately 50% of baseline values. Both compounds also increased PTyr-P two- to three-fold immediately, with levels returning to baseline at 4h. Similarly, two- to three-fold increases in [Ca2+]i were noted after 1 min exposure. [Ca2+]i increased progressively, reaching levels five- to eight-fold greater than control values. In contrast, dye uptake was delayed with HgCl2 and p-CMB, although cell death proceeded rapidly, with almost all non-viable cells being late apoptotic (YP+/PI+) by 4h. p-CMB produced early reductions in F-actin, and after 4h, complete loss of F-actin with only partial reduction of total beta-tubulin was seen with both p-CMB and HgCl2. HgCl2 reduced CD3 expression and PTyr-P slightly within minutes, while p-CMB produced similar effects on CD3 only at 4h, at which time PTyr-P was increased two- to three-fold. Both compounds increased [Ca2+]i within minutes, though levels remained under twice the baseline concentration after 15 min exposure. With continued exposure, [Ca2+]i increased to levels two- to five-fold greater than control values. These findings indicate the two groups of Hg compounds may induce cell death by distinct pathways, reflecting interactions with different cellular targets leading to cell death.