Decrease of NADH in yeast cells by external ferricyanide reduction

Cytotoxic effects of menadione on normal and cytochrome c-deficient yeast cells cultivated aerobically or anaerobically

Cytotoxic effects of menadione on normal and cytochrome c-deficient yeast cells were examined on the basis of the cell growth rate, NAD(P)H concentration, reactive oxygen production, plasma membrane H⁺-ATPase activity, and ethanol production. In aerobically or anaerobically cultured yeast cells, NAD(P)H concentration decreased with increasing concentration of menadione, and the recovery of NAD(P)H concentration was proportional to the cell growth rate. However, there was no relationship among the inhibition of the cell growth and reactive oxygen production, plasma membrane H⁺-ATPase activity, and ethanol production. Among them, ethanol production showed resistance to the cytotoxicity of menadione, suggesting the resistance of glycolysis to menadione. The growth inhibitory effect of menadione depended on the rapid decrease and the recovery of NAD(P)H rather than production of reactive oxygen species regardless of aerobic culture or anaerobic culture and presence or absence of mitochondrial function. The recovery of NAD(P)H concentration after the addition of menadione might depend on menadione-resistant glycolytic enzymes.

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The rapid decrease in NAD(P)H concentration in yeast cells was observed after the addition of menadione.

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The recovery of NAD(P)H concentration after addition of menadione was proportional to the cell growth rate.

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The above phenomena were observed in suspension of aerobically or anaerobically cultured yeast cells.

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The above phenomena were observed in suspension of normal or cytochrome c-deficient yeast cells.

Different characteristics between menadione and menadione sodium bisulfite as redox mediator in yeast cell suspension

Menadione promoted the production of active oxygen species (AOS) in both yeast cell suspension and the crude enzymes from the cells, but menadione sodium bisulfite (MSB) had little effect on the production of AOS in the cell suspension. MSB kept the stable increase in the electron transfer from intact yeast cells to anode compared to menadione, but the electron transfer promoted by MSB was inhibited in permeabilized yeast cell suspension. Menadione promoted oxidation of NAD(P)H much faster than MSB in permeabilized yeast cell suspension, suggesting the oxidative stress due to consumption of NAD(P)H. The proliferation of yeast cells was inhibited by menadione under aerobic conditions rather than anaerobic conditions, and the inhibitory effect was reduced by superoxide dismutase and catalase. The effect of MSB on the proliferation was much smaller than that of menadione. The above facts suggest that harmless MSB promotes the electron transfer from plasma membrane of yeast cells to anode. On the other hand, harmful menadione might promote the electron transfer from cytosol and plasma membrane to anode and dissolved oxygen.

The different behaviors of three oxidative mediators in probing the redox activities of the yeast Saccharomyces cerevisiae

The different behaviors of three lipophilic mediators including 2-methyl-1,4-naphthalenedione(menadione), 2,6-dichlorophenolindophenol (DCPIP) and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) in probing the redox activity of the yeast Saccharomyces cerevisiae were studied by several comparative factor-influencing experiments. Hydrophilic ferricyanide was employed as an extracellular electron acceptor, and constituted dual mediator system with each of three lipophilic mediators. Limiting-current microelectrode voltammetry was used to measure the quantity of ferrocyanide accumulations, giving a direct measure of the redox activity. It was found that under anaerobic condition, menadione interacts with anaerobic respiration pathway, whereas DCPIP and TMPD interact with fermentation pathway in the yeast. Based on the understanding of the interaction between the yeast and each of three mediators, three mediators were respectively employed in evaluating the toxicity of acetic acid on S. cerevisiae and, the results for the first showed that the mediators are complementary to each other when used as electron carriers in biotoxicity assay.

Triton X-100 inhibition of yeast plasma membrane associated NADH-dependent redox activities

Plasma membrane (PM) vesicles isolated from the yeast Saccharomyces cerevisiae (wild-type NCIM 3078, and a MG 21290 mutant pma 1-1) were used to monitor the effect of the detergents, 3-[(3-cholamidopropyl) dimethylammonio]-1-propane sulfonate (Chaps) and Triton X-100, on (H+)-ATPase (E.C. 3.6.1.35), NADH oxidase and NADH-hexacynoferrate (III)[HCF (III)] oxidoreductase (E.C. 1.6.99.3) activities. The results obtained show that Triton X-100 inhibited both membrane bound and solubilized NADH-dependent redox activities. The nature of this inhibition as determined for NADH-HCF(III) oxidoreductase was non-competitive and the Ki values for wild and mutant enzymes were 1.2 x 10(-5) M and 8.0 x 10(-6) M, respectively. The findings are interpreted, in view of the established reports, that the active site architecture of PM bound NADH-dependent oxidoreductase in yeast is likely to be different than in other eukaryotes.

A glucose-activated electron transfer system in the plasma membrane stimulates the H(+)-ATPase in Penicillium cyclopium

Hyphal cells of three fungal species of the genus Penicillium reduced the nonpermeable, external electron acceptor hexabromoiridate IV (HBI IV). In Penicillium cyclopium, the rate of HBI IV reduction by hyphal cells was drastically increased by the addition of beta-glucose. The stimulation showed high specificity for this sugar and did not require its uptake and cellular metabolism. Cell wall oxidases (e.g., glucose oxidase) did not seem to be involved in the reduction of HBI IV, as no measurable H2O2 was formed from added glucose and removal of oxygen had no effect. We propose that there is a glucose-binding component outside the plasma membrane which controls transmembrane electron fluxes in response to external glucose. Reduction of HBI IV was accompanied by rapid acidification of the cellular interior (measured by confocal pH topography). Subsequently, the outer medium was acidified of the cellular interior (measured by confocal pH topography). Subsequently, the outer medium was acidified with an e-/H+ stoichiometry of > 1. In plasma membrane vesicles containing endogenous electron donors, the membrane-residing fluoroprobe Di-8-ANEPPS reported a transient depolarization of the membrane potential triggered by the external electron acceptor. Inhibitors of ATP-dependent proton pumping enhanced the extent of this depolarization, inhibited the subsequent normalization of membrane potential, and, in whole cells, reduced the amount of redox-triggered proton extrusion. From these and other findings, it is concluded that the observed trans-plasma membrane redox process activates the H(+)-ATPase via membrane depolarization and cytosolic acidification.

Two distinctly regulated genes are required for ferric reduction, the first step of iron uptake in Saccharomyces cerevisiae

Iron uptake in Saccharomyces cerevisiae involves at least two steps: reduction of ferric to ferrous ions extracellularly and transport of the reduced ions through the plasma membrane. We have cloned and molecularly characterized FRE2, a gene which is shown to account, together with FRE1, for the total membrane-associated ferric reductase activity of the cell. Although not similar at the nucleotide level, the two genes encode proteins with significantly similar primary structures and very similar hydrophobicity profiles. The FRE1 and FRE2 proteins are functionally related, having comparable properties as ferric reductases. FRE2 expression, like FRE1 expression, is induced by iron deprivation, and at least part of this control takes place at the transcriptional level, since 156 nucleotides upstream of the initiator AUG conferred iron-dependent regulation when fused to a heterologous gene. However, the two gene products have distinct temporal regulation of their activities during cell growth.

Two distinctly regulated genes are required for ferric reduction, the first step of iron uptake in Saccharomyces cerevisiae

Iron uptake in Saccharomyces cerevisiae involves at least two steps: reduction of ferric to ferrous ions extracellularly and transport of the reduced ions through the plasma membrane. We have cloned and molecularly characterized FRE2, a gene which is shown to account, together with FRE1, for the total membrane-associated ferric reductase activity of the cell. Although not similar at the nucleotide level, the two genes encode proteins with significantly similar primary structures and very similar hydrophobicity profiles. The FRE1 and FRE2 proteins are functionally related, having comparable properties as ferric reductases. FRE2 expression, like FRE1 expression, is induced by iron deprivation, and at least part of this control takes place at the transcriptional level, since 156 nucleotides upstream of the initiator AUG conferred iron-dependent regulation when fused to a heterologous gene. However, the two gene products have distinct temporal regulation of their activities during cell growth.

Ferric reductase of Saccharomyces cerevisiae: molecular characterization, role in iron uptake, and transcriptional control by iron

The principal iron uptake system of Saccharomyces cerevisiae utilizes a reductase activity that acts on ferric iron chelates external to the cell. The FRE1 gene product is required for this activity. The deduced amino acid sequence of the FRE1 protein exhibits hydrophobic regions compatible with transmembrane domains and has significant similarity to the sequence of the plasma membrane cytochrome b558 (the X-CGD protein), a critical component of a human phagocyte oxidoreductase, suggesting that FRE1 is a structural component of the yeast ferric reductase. FRE1 mRNA levels are repressed by iron. Fusion of 977 base pairs of FRE1 DNA upstream from the translation start site of an Escherichia coli lacZ reporter gene confers iron-dependent regulation on expression of beta-galactosidase in yeast. An 85-base-pair segment of FRE1 5' noncoding sequence contains a RAP1 binding site and a repeated sequence, TTTTTGCTCAYC; this segment is sufficient to confer iron-repressible transcriptional activity on heterologous downstream promoter elements.

Transplasma membrane electron transport in plants

The presence of transplasma membrane electron transport in a variety of plant cells and tissues is reported. It is now agreed that this property of eukaryotic cells is of ubiquitous nature. Studies with highly purified plasma membranes have established the presence of electron transport enzymes. Two types of activities have been identified. One, termed "Standard" reductase, is of general occurrence. The other, inducible under iron deficiency and relatively more active, is "Turbo" reductase. However, the true nature of components participating in electron transport and their organization in the plasma membrane is not known. The electron transport is associated with proton release and uses intracellular NAD(P)H as substrate. The electron flow leads to changes in intracellular redox status, pH, and metabolic energy. The responsiveness of this system to growth hormones is also observed. These findings suggest a role for electron flow across the plasma membrane in cell growth and regulation of ion transport. Involvement of this system in many other cellular functions is also argued.

Chemiluminescent assay for determination of viable cell density of yeast, mammalian, and plant cells

The production of H2O2 by intact cells is promoted in the presence of menadione and is proportional to the density of viable cells. The concentration of H2O2 produced is determined by the measurement of chemiluminescence which is generated in the mixture of H2O2, pyrene, and bis(2,4,6-trichlorophenyl)oxalate. This method is applied to the measurement of viable yeast, mammalian, and plant cells. For example, viable yeast cell density above 10(4) cells/ml is determined for 2 min, and mammalian cell density and the activity of plant tissues are determined for 10 and 5 min, respectively.

Changes in intracellular redox and energy status during induced transplasma membrane electron transport in Cuscuta protoplasts

Extracellular reduction of ferricyanide was exhibited by isolated Cuscuta protoplasts. A larger decrease in NADH than NADPH levels of the ferricyanide-treated protoplasts pointed to the major involvement of the former as an electron donor. Glutathione levels were also found to be lowered in similarly treated tissue. The time-dependent variation in intracellular ATP levels in presence of ferricyanide supported the concept of plasma membrane ATPase activation during transplasma membrane electron transport in eukaryotes.