Depletion of glutathione as a cause of the promotive effects of polygodial, a sesquiterpene on the production of reactive oxygen species in Saccharomyces cerevisiae

Anti-Yeast Synergistic Effects and Mode of Action of Australian Native Plant Essential Oils

Yeasts are the most common group of microorganisms responsible for spoilage of soft drinks and fruit juices due to their ability to withstand juice acidity and pasteurization temperatures and resist the action of weak-acid preservatives. Food industries are interested in the application of natural antimicrobial compounds as an alternative solution to the spoilage problem. This study attempts to investigate the effectiveness of three Australian native plant essential oils (EOs) Tasmanian pepper leaf (TPL), lemon myrtle (LM) and anise myrtle (AM) against weak-acid resistant yeasts, to identify their major bioactive compounds and to elucidate their anti-yeast mode of action. The minimum inhibitory concentration (MIC), minimum fungicidal concentration (MFC) and minimum bactericidal concentration (MBC) were assessed for EOs against weak-acid resistant yeasts (Candida albicans, Candida krusei, Dekkera anomala, Dekkera bruxellensis, Rhodotorula mucilaginosa, Saccharomyces cerevisiae, Schizosaccharomyces pombe, Zygosaccharomyces bailii and Zygosaccharomyces rouxii) and bacteria (Staphylococcus aureus and Escherichia coli). The EOs showed anti-yeast and antibacterial activity at concentrations ranging from 0.03–0.07 mg/mL and 0.22–0.42 mg/mL for TPL and 0.07–0.31 mg/mL and 0.83–1.67 mg/mL for LM, respectively. The EOs main bioactive compounds were identified as polygodial in TPL, citral (neral and geranial) in LM and anethole in AM. No changes in the MICs of the EOs were observed in the sorbitol osmotic protection assay but were found to be increased in the ergosterol binding assay after the addition of exogenous ergosterol. Damaging of the yeast cell membrane, channel formation, cell organelles and ion leakage could be identified as the mode of action of TPL and LM EOs. The studied Australian native plant EOs showed potential as natural antimicrobials that could be used in the beverage and food industry against the spoilage causing yeasts.

Antimicrobial Activity of Nanoencapsulated Essential Oils of Tasmannia lanceolata, Backhousia citriodora and Syzygium anisatum against Weak-Acid Resistant Zygosaccharomyces bailii in Clear Apple Juice

The anti-yeast activity of oil-in-water encapsulated nanoemulsion containing individual or a combination of the three essential oils of Tasmanian pepper leaf (Tasmannia lanceolata), lemon myrtle (Backhousia citriodora), and anise myrtle (Syzygium anisatum) against weak-acid resistant Zygosaccharomyces bailii in clear apple juice was investigated. The effectiveness of the shelf-life extension of Z. bailii-spiked (1 × 103 CFU/mL) clear apple juice was evaluated and compared between natural (essential oils) and synthetic (sodium benzoate) antimicrobial agents. Essential oils showed an immediate reduction in the Z. bailii cell population at day-0 and exerted a fungicidal activity at day-4 of storage, with no further noticeable growth at the end of the experiment (day-28). At lower concentrations, Tasmanian pepper leaf oil of 0.0025% had >6 log CFU/mL at day-12 of storage. For lemon myrtle essential oils, the yeast population reached >6 log CFU/mL at day-24 and day-20 for concentrations of 0.02% and 0.01%, respectively. The fungicidal activity of Tasmanian pepper leaf oil reduced from 0.005% to 0.0025% v/v when mixed at a ratio of 1:1 with anise myrtle oil. The results of the present study suggest that these three native Australian herbs have the potential to be used in the beverage industry by controlling Zygosaccharomyces bailii in clear apple juice products.

Investigating the Antifungal Mechanism of Action of Polygodial by Phenotypic Screening in Saccharomyces cerevisiae

Polygodial is a "hot" peppery-tasting sesquiterpenoid that was first described for its anti-feedant activity against African armyworms. Using the haploid deletion mutant library of Saccharomyces cerevisiae, a genome-wide mutant screen was performed to shed more light on polygodial's antifungal mechanism of action. We identified 66 deletion strains that were hypersensitive and 47 that were highly resistant to polygodial treatment. Among the hypersensitive strains, an enrichment was found for genes required for vacuolar acidification, amino acid biosynthesis, nucleosome mobilization, the transcription mediator complex, autophagy and vesicular trafficking, while the resistant strains were enriched for genes encoding cytoskeleton-binding proteins, ribosomal proteins, mitochondrial matrix proteins, components of the heme activator protein (HAP) complex, and known regulators of the target of rapamycin complex 1 (TORC1) signaling. WE confirm that polygodial triggers a dose-dependent vacuolar alkalinization and that it increases Ca²⁺ influx and inhibits glucose-induced Ca²⁺ signaling. Moreover, we provide evidence suggesting that TORC1 signaling and its protective agent ubiquitin play a central role in polygodial resistance, suggesting that they can be targeted by polygodial either directly or via altered Ca²⁺ homeostasis.

Probing the Structure-Activity Relationship of the Natural Antifouling Agent Polygodial against both Micro- and Macrofoulers by Semisynthetic Modification

The current study represents the first comprehensive investigation into the general antifouling activities of the natural drimane sesquiterpene polygodial. Previous studies have highlighted a high antifouling effect toward macrofoulers, such as ascidians, tubeworms, and mussels, but no reports about the general antifouling effect of polygodial have been communicated before. To probe the structural and chemical basis for antifouling activity, a library of 11 polygodial analogues was prepared by semisynthesis. The library was designed to yield derivatives with ranging polarities and the ability to engage in both covalent and noncovalent interactions, while still remaining within the drimane sesquiterpene scaffold. The prepared compounds were screened against 14 relevant marine micro- and macrofouling species. Several of the polygodial analogues displayed inhibitory activities at sub-microgram/mL concentrations. These antifouling effects were most pronounced against the macrofouling ascidian Ciona savignyi and the barnacle Balanus improvisus, with inhibitory activities observed for selected compounds comparable or superior to several commercial antifouling products. The inhibitory activity against the microfouling bacteria and microalgae was reversible and significantly less pronounced than for the macrofoulers. This study illustrates that the macro- and microfoulers are targeted by the compounds via different mechanisms.

Ethnobotanical, Phytochemical, Pharmacological, and Toxicological Aspects of Persicaria hydropiper (L.) Delarbre

Persicaria hydropiper (L.) Delarbre, belonging to Polygonaceae family, is a common weed found in most of the temperate countries including Bangladesh, China, Malaysia, and Japan. The plant is also referred to as “marsh pepper” or “smart weed.” It appears to be a useful herb with evidence-based medicinal properties. The present work addresses the botanical description, traditional uses, phytochemistry, pharmacology, and toxicology of P. hydropiper. All plant parts have been commonly used in the traditional systems of medicines. Flavonoids are the major group of phytochemical components followed by drimane-type sesquiterpenes and sesquiterpenoids, as well as phenylpropanoids. Different extracts and plant parts showed remarkable pharmacological activities including antioxidant, antibacterial, antifungal, antihelminth, antifeedant, cytotoxicity, anti-inflammatory, antinociceptive, oestrogenicity, antifertility, antiadipogenicity, and neuroprotection. Mutagenicity and acute and subchronic toxicities of the plant were also reported. P. hydropiper has tremendous medicinal properties that could further be investigated for the development of evidence-based herbal products.

Melanogenesis inhibitors from Rabdosia japonica

The effects of the four major ent-kaurene diterpenoids isolated from the aerial part of Rabdosia japonica (Labiatae) on murine B16-F10 melanoma cells were investigated. Among the compounds tested, oridonin and nodosin most significantly suppressed cellular melanin production when the cells were cultured with these diterpenoids. However, oridonin and nodosin exhibited cytotoxicity against the same melanoma cells with an IC(50) of 1.1 μM (0.40 μg/ml) and of 1.3 μM (0.47 μg/ml) and almost complete lethality was observed at 4.0 μM and at 8.0 μM, respectively, and therefore observed melanogenesis inhibition is mainly due to its melanocytotoxic effect. Morphological observation showed that oridonin or nodosin treated B16-F10 melanoma cells induced dendrite structure. Diterpenoids quickly formed adducts partly in Dulbecco's Modified Eagle's Medium (DMEM) containing 10% of fetal bovine serum (10% FBS-DMEM) before their application to the cells. Approximately 20% of oridonin formed adducts within the first 15 min. Notably, dihydronodosin exhibited inferior cytotoxicity (>85% cell viability at 100 μM) but still significantly suppressed melanogenesis (>55%) when murine B16-F10 melanoma cells were cultured with this diterpenoid derivatives. Hence, dihydronodosin can be a potential melanogenesis inhibitor.

Adaptive stress response to menadione-induced oxidative stress in Saccharomyces cerevisiae KNU5377

The molecular mechanisms involved in the ability of yeast cells to adapt and respond to oxidative stress are of great interest to the pharmaceutical, medical, food, and fermentation industries. In this study, we investigated the time-dependent, cellular redox homeostasis ability to adapt to menadione-induced oxidative stress, using biochemical and proteomic approaches in Saccharomyces cerevisiae KNU5377. Time-dependent cell viability was inversely proportional to endogenous amounts of ROS measured by a fluorescence assay with 2',7'-dichlorofluorescin diacetate (DCFHDA), and was hypersensitive when cells were exposed to the compound for 60 min. Morphological changes, protein oxidation and lipid peroxidation were also observed. To overcome the unfavorable conditions due to the presence of menadione, yeast cells activated a variety of cell rescue proteins including antioxidant enzymes, molecular chaperones, energy-generating metabolic enzymes, and antioxidant molecules such as trehalose. Thus, these results show that menadione causes ROS generation and high accumulation of cellular ROS levels, which affects cell viability and cell morphology and there is a correlation between resistance to menadione and the high induction of cell rescue proteins after cells enter into this physiological state, which provides a clue about the complex and dynamic stress response in yeast cells.

Genotoxicity of 15-deoxygoyazensolide in bacteria and yeast

Sesquiterpene lactones (SLs) present a wide range of pharmacological activities. The aim of our study was to investigate the genotoxicity of 15-deoxygoyazensolide using the Salmonella/microsome assay and the yeast Saccharomyces cerevisiae. We also investigated the nature of induced DNA damage using yeast strains defective in DNA repair pathways, such as nucleotide excision repair (RAD3), error prone repair (RAD6), and recombinational repair (RAD52), and in DNA metabolism, such as topoisomerase mutants. 15-deoxygoyasenzolide was not mutagenic in Salmonella typhimurium, but it was mutagenic in S. cerevisiae. The hypersensitivity of the rad52 mutant suggests that recombinational repair is critical for processing lesions resulting from 15-deoxygoyazensolide-induced DNA damage, whereas excision repair and mutagenic systems does not appear to be primarily involved. Top 1 defective yeast strain was highly sensitive to the cytotoxic activity of 15-deoxygoyazensolide, suggesting a possible involvement of this enzyme in the reversion of the putative complex formation between DNA and this SL, possibly due to intercalation. Moreover, the treatment with this lactone caused dose-dependent glutathione depletion, generating pro-oxidant status which facilitates oxidative DNA damage, particularly DNA breaks repaired by the recombinational system ruled by RAD52 in yeast. Consistent with this finding, the absence of Top1 directly affects chromatin remodeling, allowing repair factors to access oxidative damage, which explains the high sensitivity to top1 strain. In summary, the present study shows that 15-deoxygoyazensolide is mutagenic in yeast due to the possible intercalation effect, in addition to the pro-oxidant status that exacerbates oxidative DNA damage.

Involvement of oxidative stress induction in Na+ toxicity and its relation to the inhibition of a Ca2+ -dependent but calcineurin-independent mechanism in Saccharomyces cerevisiae

Uridine 5'-hexadecylphosphate (UMPC16) inhibited the growth of Saccharomyces cerevisiae under a hypersaline stress condition with Na+ more strongly than the calcineurin inhibitor cyclosporine A (CsA). Additional Ca2+ supplementation similarly suppressed the inhibitory activities of UMPC16 and CsA on yeast cell growth in a medium with Na+. UMPC16, but not CsA, accelerated mitochondrial reactive oxygen species (ROS) generation in combination with Na+, suggesting its inhibition of a Ca2+ -dependent but calcineurin-independent mechanism for protection against Na+ toxicity.

Pro-oxidant action of diphenyl diselenide in the yeast Saccharomyces cerevisiae exposed to ROS-generating conditions

Organoselenium compounds have a potential thiol peroxidase-like activity. Diphenyl diselenide (DPDS) is an electrophilic reagent used in the synthesis of a variety of pharmacologically active organic selenium compounds. Using TRAP assay of chemiluminescense we have shown that diphenyl diselenide clearly possesses a pro-oxidant property. For an investigation on the mechanisms of this property, we used mutant strains of Saccharomyces cerevisiae defective in antioxidant defenses, i.e. in superoxide dismutase, in biosynthesis of glutathione, and the transcription factor yAP-1-lacking yap 1 mutant that cannot activate genes of the oxidative stress response. Exposure of growing cultures to the drug increased cell sensitivity to oxidizing agents. The pro-oxidant effect was independent of the metabolic condition or of the oxidative mutagen tested. N-acetylcysteine, a precursor of glutathione biosynthesis, could neutralize the pro-oxidant effects of diphenyl diselenide by stimulating an increase of endogenous glutathione biosynthesis or by directly binding to the drug. Vitamin E (Trolox), a known antioxidant, was also able to protect S. cerevisiae against the pro-oxidant effect of diphenyl diselenide. In vitro assays showed that diphenyl diselenide interacts non-enzymatically with the thiol group of glutathione.

Multifunctional action of antifungal polygodial against Saccharomyces cerevisiae: involvement of pyrrole formation on cell surface in antifungal action

The antifungal activity of polygodial against Saccharomyces cerevisiae involves multifunctions. Polygodial first acts as a surface-active agent (surfactant) and then becomes involved in biochemical processes. The ability to form a pyrrole derivative with a primary amine group of phosphatidylethanolamine (PE) and phosphatidylserine (PS) in the outer monolayer of the plasma membrane is likely, in part, an initial step in the antifungal action of polygodial. In the lipid fraction derived from cells treated with polygodial, no PE and PS were detected, indicating a disturbance in the balance of the plasma membrane. The primary antifungal action of polygodial comes from its ability to act as a surfactant that nonspecifically disrupts the lipid-protein interface of integral proteins, denaturing their functioned conformation. Once polygodial enters the cytoplasm by destroying the membrane barrier, it reacts with L-cystein-containing cytoplasmic materials, such as a small molecule, glutathione, and a protein, alcohol dehydrogenase, to potentiate the antifungal action.

Synergistic fungicidal activity of Cu(2+) and allicin, an allyl sulfur compound from garlic, and its relation to the role of alkyl hydroperoxide reductase 1 as a cell surface defense in Saccharomyces cerevisiae

Cu(2+) showed a dose-dependent fungicidal activity against Saccharomyces cerevisiae cells, and its lethal effect was extremely enhanced in the presence of allicin, an allyl sulfur compound from garlic. The fungicidal activity of Cu(2+) was unaffected or rather attenuated by other sulfur-containing compounds such as N-acetyl-cysteine, l-cysteine or dithiothreitol. Ca(2+) could absolutely protect against the lethal effect of Cu(2+) itself, but showed no protection against the fungicidal activity of Cu(2+) newly generated in combination with allicin. Cu(2+) accelerated an endogenous generation of reactive oxygen species (ROS) in S. cerevisiae cells at a lethal concentration, but such intracellular oxidative stress induction was not observed during cell death progression upon treatment with Cu(2+) and allicin. A surfactant, sodium N-lauroyl sarcosinate (SLS), enhanced the solubilization of a few proteins including alkyl hydroperoxide reductase 1 (AHP1) in intact cells, accounting for the absence of this protein in the extract from allicin-treated cells. Allicin-treated cells were rendered extremely sensitive to the subsequent Cu(2+) treatment as in the case of SLS-treated cells. Allicin-treated cells and SLS-treated cells similarly showed an increased sensitivity to exogenously added tert-butyl hydroperoxide (t-BOOH), an organic peroxide that is detoxified by the action of AHP1. Our study suggests that allicin influences the mode of cell surface localization or the related function of AHP1 as a defense against phospholipid peroxidation by the external action of Cu(2+).

Inhibition of the mitochondrial ATP synthesis by polygodial, a naturally occurring dialdehyde unsaturated sesquiterpene

Polygodial is a naturally occurring sesquiterpene dialdehyde that exhibits several pharmacologically interesting activities. Among them, its antifungal properties have been more thoroughly studied. The mitochondrial ATPase has been suggested as one of the possible targets for polygodial action. However, its mechanism of action is not well defined yet. The effect of polygodial on the mitochondrial energy metabolism is described in this paper. Polygodial inhibited ATP synthesis coupled to succinate oxidation in beef-heart submitochondrial particles at concentrations (IC(50)=2.4+/-0.1 microM) which marginally affected electron transport and ATPase activity (IC(50)=97+/-4 microM). A transitory stimulation of the electron transport in intact rat liver mitochondria in state 4 was also obtained at low polygodial concentrations (EC(50)=20+/-4 microM). These results suggest that polygodial uncouples ATP synthesis from electron transport at low concentrations. Similar concentrations of polygodial partially abolished the ANS fluorescence enhancement (IC(50)=2.2+/-0.4 microM) induced by succinate oxidation in submitochondrial particles but did not collapse the DeltapH. We postulate that polygodial uncouples mitochondrial ATP synthesis by affecting the electrical properties of the membrane surface and consequently collapsing the membrane potential (Deltapsi) and/or the localized transmembrane pH difference (DeltapH(S)) without affecting the DeltapH between the two bulk aqueous phases (DeltapH(B)). The relevance of these findings for the understanding of the biochemical basis of the antifungal activity of polygodial and the evaluation of its potentiality as a therapeutic agent are discussed.

Naturally occurring antifungal agents against Zygosaccharomyces bailii and their synergism

Polygodial was found to exhibit a fungicidal activity against a food spoilage yeast, Zygosaccharomyces bailii, with the minimum fungicidal concentration (MFC) of 50 microg/mL (0.17 mM). The time-kill curve study showed that polygodial was fungicidal at any growth stage. The primary action of polygodial comes from its ability to disrupt the native membrane-associated function of integral proteins as nonionic surface active agents (surfactants) followed by a decrease in plasma membrane fluidity. The fungicidal activity of polygodial was increased 128-fold in combination with a sublethal amount (equivalent of 1/2 MFC) of anethole and vice versa relative to the fungicidal activity of anethole. The fungicidal activity of sorbic acid was enhanced 512-fold in combination with 1/2 MFC of polygodial. Conversely, the fungicidal activity of polygodial was enhanced 128-fold in combination with 1/2 MFC of sorbic acid.

Effect of EDTA alone and in combination with polygodial on the growth of Saccharomyces cerevisiae

The antifungal activity of ethylenediaminetetraacetic acid (EDTA) against Saccharomyces cerevisiae was significantly affected by various conditions such as inoculum size, pH, and metal ions (Mg(2+), Ca(2+)). EDTA was found to be effective against this yeast at the inoculum size of 10(5) colony forming units (CFU)/mL with the minimum inhibitory concentration of 400 mug/mL and the minimum fungicidal concentration of 6400 mug/mL, but it was not effective at 10(7) CFU/mL up to 6400 mug/mL. The fungicidal activity of EDTA against S. cerevisiae was significantly enhanced in combination with polygodial. Isobolograms, fractional inhibitory concentration, and fractional fungicidal concentration indices were used for evaluating the interaction between combined compounds. This synergistic effect is likely due to polygodial's destructive action on the cellular membrane, which facilitates the transmembrane transport of foreign compounds (EDTA) into yeast cells. Once inside the cells, EDTA forms chelation with divalent metals such as Mg(2+) and Ca(2+), which are required by various essential enzymes.

Screening for microtubule-disrupting antifungal agents by using a mitotic-arrest mutant of Aspergillus nidulans and novel action of phenylalanine derivatives accompanying tubulin loss

The microtubule, which is one of the major targets of anthelmintics, anticancer drugs, and fungicides, is composed mainly of alpha- and beta-tubulins. We focused on a unique characteristic of an Aspergillus nidulans benA33 mutant to screen for microtubule-disrupting antifungal agents. This mutant, which has a beta-tubulin with a mutation of a single amino acid, undergoes mitotic arrest due to the formation of hyperstable microtubules at 37 degrees C. The heat sensitivity of the mutant is remedied by some antimicrotubule agents. We found that an agar plate assay with the mutant was able to distinguish three types of microtubule inhibitors. The growth recovery zones of the mutant were formed around paper disks containing microtubule inhibitors, including four benzimidazoles, ansamitocin P-3, griseofulvin, and rhizoxin, on the agar plate at 37 degrees C. Nocodazole, thiabendazole, and griseofulvin reversed the mitotic arrest of the mutant and promoted its hyphal growth. Ansamitocin P-3 and rhizoxin showed growth recovery zones around the growth-inhibitory zones. Benomyl and carbendazim also reversed mitotic arrest but produced weaker growth recovery than the aforementioned drugs. Other microtubule inhibitors, such as colchicine, Colcemid, paclitaxel, podophyllotoxin, TN-16, vinblastine, and vincristine, as well as some cytoskeletal inhibitors tested, did not show such activity. In our screening, we newly identified two mycotoxins, citrinin and patulin, two sesquiterpene dialdehydes, polygodial and warburganal, and four phenylalanine derivatives, arphamenine A, L-2,5-dihydrophenylalanine (DHPA), N-tosyl-L-phenylalanine chloromethylketone, and N-carbobenzoxy-L-phenylalanine chloromethyl ketone. In a wild-type strain of A. nidulans, DHPA caused selective losses of microtubules, as determined by fluorescence microscopy, and of both alpha- and beta-tubulins, as determined by Western blot analysis. This screening method involving the benA33 mutant of A. nidulans is useful, convenient, and highly selective. The phenylalanine derivatives tested are of a novel type of microtubule-disrupting antifungal agents, producing an accompanying loss of tubulins, and are different from well-known tubulin inhibitors affecting the assembly of tubulin dimers into microtubules.

Glutathione, Altruistic Metabolite in Fungi

Glutathione (GSH; gamma-L-glutamyl-L-cysteinyl-glycine), a non-protein thiol with a very low redox potential (E'0 = 240 mV for thiol-disulfide exchange), is present in high concentration up to 10 mM in yeasts and filamentous fungi. GSH is concerned with basic cellular functions as well as the maintenance of mitochondrial structure, membrane integrity, and in cell differentiation and development. GSH plays key roles in the response to several stress situations in fungi. For example, GSH is an important antioxidant molecule, which reacts non-enzymatically with a series of reactive oxygen species. In addition, the response to oxidative stress also involves GSH biosynthesis enzymes, NADPH-dependent GSH-regenerating reductase, glutathione S-transferase along with peroxide-eliminating glutathione peroxidase and glutaredoxins. Some components of the GSH-dependent antioxidative defence system confer resistance against heat shock and osmotic stress. Formation of protein-SSG mixed disulfides results in protection against desiccation-induced oxidative injuries in lichens. Intracellular GSH and GSH-derived phytochelatins hinder the progression of heavy metal-initiated cell injuries by chelating and sequestering the metal ions themselves and/or by eliminating reactive oxygen species. In fungi, GSH is mobilized to ensure cellular maintenance under sulfur or nitrogen starvation. Moreover, adaptation to carbon deprivation stress results in an increased tolerance to oxidative stress, which involves the induction of GSH-dependent elements of the antioxidant defence system. GSH-dependent detoxification processes concern the elimination of toxic endogenous metabolites, such as excess formaldehyde produced during the growth of the methylotrophic yeasts, by formaldehyde dehydrogenase and methylglyoxal, a by-product of glycolysis, by the glyoxalase pathway. Detoxification of xenobiotics, such as halogenated aromatic and alkylating agents, relies on glutathione S-transferases. In yeast, these enzymes may participate in the elimination of toxic intermediates that accumulate in stationary phase and/or act in a similar fashion as heat shock proteins. GSH S-conjugates may also form in a glutathione S-transferases-independent way, e.g. through chemical reaction between GSH and the antifugal agent Thiram. GSH-dependent detoxification of penicillin side-chain precursors was shown in Penicillium sp. GSH controls aging and autolysis in several fungal species, and possesses an anti-apoptotic feature.

Oxidative stress-dependent inhibition of yeast cell growth by farnesylamine and its possible relation to amine oxidase in the mitochondrial fraction

Among various analogs of the isoprenoid farnesol (FOH), farnesylamine (FNH2) inhibited the growth of the budding yeast Saccharomyces cerevisiae by accelerating cellular reactive oxygen species (ROS) generation. Unlike the case with FOH, however, FNH2 did not cause mitochondrial transmembrane potential (mtDeltaPsi) hyperpolarization so that FNH2-treated cells were not protected against ROS production by inhibiting the proton pumping function of mitochondrial F(O)F1-ATPase. FNH2 promoted ROS generation even in cells of a respiration-deficient mutant, indicating a yeast metabolic pathway other than mitochondrial electron transport as the origin of ROS. FNH2 oxidase activity was detected in the yeast mitochondrial fraction, which produces hydrogen peroxide (H2O2) in the reaction with either FNH2 or geranylgeranylamine (GGNH2), in addition to polyamine oxidase activity specific for spermine. GGNH2 also exhibited the growth inhibitory effect with the accompanying induction of ROS generation, while such an activity was not detected with any of the polyamines tested or geranylamine. FNH2 oxidase, which was sensitive to a typical copper-chelating agent, diethyldithiocarbamic acid (DDC), could be solubilized with Triton X-100, and detected as a single band upon activity staining with FNH2 but not with spermine in polyacrylamide gel electrophoresis. FNH2-treated cells were partly protected against ROS production by the additional supplementation of DDC in the medium. Our results suggest the involvement of H2O2 production due to direct oxidation of FNH2 by copper amine oxidase in oxidative stress-dependent inhibition of yeast cell growth.

Oxidative stress induction as a cause of Ba2+-dependent fungicidal action of UMP-derivative on the yeast Shizosaccharomyces pombe

A UMP-derivative, uridine 5'-hexadecylphosphate (UMPC16), exhibited a fungicidal action against various yeast strains including the fission yeast Schizosaccharomyces pombe in combination with Ba2+ ion. UMPC16 accelerated reactive oxygen species (ROS) generation in medium with Ba2+ ion in a dose- and time-dependent manner. Additional supplementation of Ca2+ ion into medium could suppress such a combined fungicidal action due to oxidative stress induction.