Transplasma membrane electron transport: enzymes involved and biological function

Electrochemical assay of mammalian cell viability

We present the first use of amperometric detection to assess the viability of mammalian cells in continuous mode, directly in the cell culture medium. Vero or HeLa cells were injected into electrochemical sensors equipped with a 3-electrode system and containing DCIP 50 µM used as the redox mediator. DCIP was reduced by the viable cells and the reduced form was detected amperometrically at 300 mV vs silver pseudo-reference. The continuous regeneration of the oxidized form of the mediator ensured a stable redox state of the cell environment, allowing the cells to survive during the measurement time. The electrochemical response was related to cell metabolism (no response with dead cells or lysed cells) and depended on both mediator concentration and cell density. The protocol was applied to both cells in suspension and adhered cells. It was also adapted to detect trans-plasma membrane electron transfer (tPMET) by replacing DCIP by ferricyanide 500 µM and using linear scan voltammetry (2 mV/s). The pioneering results described here pave the way to the development of routine electrochemical assays for cell viability and for designing a cell-based analytical platform.

Nanosecond Pulsed Electric Fields (nsPEFs) Modulate Electron Transport in the Plasma Membrane and the Mitochondria

Nanosecond pulsed electric fields (nsPEFs) are a pulsed power technology known for ablating tumors, but they also modulate diverse biological mechanisms. Here we show that nsPEFs regulate trans-plasma membrane electron transport (tPMET) rates in the plasma membrane redox system (PMRS) shown as a reduction of the cell-impermeable, WST-8 tetrazolium dye. At lower charging conditions, nsPEFs enhance, and at higher charging conditions inhibit tPMET in H9c2 non-cancerous cardiac myoblasts and 4T1-luc breast cancer cells. This biphasic nsPEF-induced modulation of tPMET is typical of a hormetic stimulus that is beneficial and stress-adaptive at lower levels and damaging at higher levels. NsPEFs also attenuated mitochondrial electron transport system (ETS) activity (O2 consumption) at Complex I when coupled and uncoupled to oxidative phosphorylation. NsPEFs generated more reactive oxygen species (ROS) in mitochondria (mROS) than in the cytosol (cROS) in non-cancer H9c2 heart cells but more cROS than mROS in 4T1-luc cancer cells. Under lower charging conditions, nsPEFs support glycolysis while under higher charging conditions, nsPEFs inhibit electron transport in the PMRS and the mitochondrial ETS producing ROS, ultimately causing cell death. The impact of nsPEF on ETS presents a new paradigm for considering nsPEF modulation of redox functions, including redox homeostasis and metabolism.

Ultra-Low Intensity Post-Pulse Affects Cellular Responses Caused by Nanosecond Pulsed Electric Fields

High-intensity nanosecond pulse electric fields (nsPEF) can preferentially induce various effects, most notably regulated cell death and tumor elimination. These effects have almost exclusively been shown to be associated with nsPEF waveforms defined by pulse duration, rise time, amplitude (electric field), and pulse number. Other factors, such as low-intensity post-pulse waveform, have been completely overlooked. In this study, we show that post-pulse waveforms can alter the cell responses produced by the primary pulse waveform and can even elicit unique cellular responses, despite the primary pulse waveform being nearly identical. We employed two commonly used pulse generator designs, namely the Blumlein line (BL) and the pulse forming line (PFL), both featuring nearly identical 100 ns pulse durations, to investigate various cellular effects. Although the primary pulse waveforms were nearly identical in electric field and frequency distribution, the post-pulses differed between the two designs. The BL's post-pulse was relatively long-lasting (~50 µs) and had an opposite polarity to the main pulse, whereas the PFL's post-pulse was much shorter (~2 µs) and had the same polarity as the main pulse. Both post-pulse amplitudes were less than 5% of the main pulse, but the different post-pulses caused distinctly different cellular responses. The thresholds for dissipation of the mitochondrial membrane potential, loss of viability, and increase in plasma membrane PI permeability all occurred at lower pulsing numbers for the PFL than the BL, while mitochondrial reactive oxygen species generation occurred at similar pulsing numbers for both pulser designs. The PFL decreased spare respiratory capacity (SRC), whereas the BL increased SRC. Only the PFL caused a biphasic effect on trans-plasma membrane electron transport (tPMET). These studies demonstrate, for the first time, that conditions resulting from low post-pulse intensity charging have a significant impact on cell responses and should be considered when comparing the results from similar pulse waveforms.

Mancozeb-induced cytotoxicity in human erythrocytes: enhanced generation of reactive species, hemoglobin oxidation, diminished antioxidant power, membrane damage and morphological changes

Mancozeb is an ethylene bis-dithiocarbamate fungicide extensively used in agriculture to safeguard crops from various fungal diseases. The general population is exposed to mancozeb through consumption of contaminated food or water. Here, we have investigated the effect of mancozeb on isolated human erythrocytes under in vitro conditions. Erythrocytes were treated with different concentrations of mancozeb (0, 5, 10, 25, 50, 100 μM) and incubated for 24 h at 37 °C. Analysis of biochemical parameters and cell morphology showed dose-dependent toxicity of mancozeb in human erythrocytes. Mancozeb treatment caused hemoglobin oxidation and heme degradation. Protein and lipid oxidation were enhanced, while a significant decrease was seen in reduced glutathione and total sulfhydryl content. A significant increase in the generation of reactive oxygen and nitrogen species was detected in mancozeb-treated erythrocytes. The antioxidant capacity and the activity of key antioxidant enzymes were greatly diminished, while crucial metabolic pathways were inhibited in erythrocytes. Damage to the erythrocyte membrane on mancozeb treatment was apparent from increased cell lysis and osmotic fragility, along with the impairment of the plasma membrane redox system. Mancozeb also caused morphological alterations and transformed the normal discoid-shaped erythrocytes into echinocytes and stomatocytes. Thus, mancozeb induces oxidative stress in human erythrocytes, impairs the antioxidant defense system, oxidizes cellular components, that will adversely affect erythrocyte structure and function.

Electric Field Induced Biomimetic Transmembrane Electron Transport Using Carbon Nanotube Porins

Cells modulate their homeostasis through the control of redox reactions via transmembrane electron transport systems. These are largely mediated via oxidoreductase enzymes. Their use in biology has been linked to a host of systems including reprogramming for energy requirements in cancer. Consequently, the ability to modulate membrane redox systems may give rise to opportunities to modulate underlying biology. The current work aims to develop a wireless bipolar electrochemical approach to form on-demand electron transfer across biological membranes. To achieve this goal, it is shown that by using membrane inserted carbon nanotube porins (CNTPs) that can act as bipolar nanoelectrodes, one can control electron flow with externally applied electric fields across membranes. Before this work, bipolar electrochemistry has been thought to require high applied voltages not compatible with biological systems. It is shown that bipolar electrochemical reaction via gold reduction at the nanotubes can be modulated at low cell-friendly voltages, providing an opportunity to use bipolar electrodes to control electron flux across membranes. The authors provide new mechanistic insight into this newly describe phenomena at the nanoscale. The results presented give rise to a new method using CNTPs to modulate cell behavior via wireless control of membrane electron transfer.

Biomolecular Basis of Cellular Consciousness via Subcellular Nanobrains

Cells emerged at the very beginning of life on Earth and, in fact, are coterminous with life. They are enclosed within an excitable plasma membrane, which defines the outside and inside domains via their specific biophysical properties. Unicellular organisms, such as diverse protists and algae, still live a cellular life. However, fungi, plants, and animals evolved a multicellular existence. Recently, we have developed the cellular basis of consciousness (CBC) model, which proposes that all biological awareness, sentience and consciousness are grounded in general cell biology. Here we discuss the biomolecular structures and processes that allow for and maintain this cellular consciousness from an evolutionary perspective.

A simple indirect colorimetric assay for measuring mitochondrial energy metabolism based on uncoupling sensitivity

Purpose

Cancer cells rapidly adjust their balance between glycolytic and mitochondrial ATP production in response to changes in their microenvironment and to treatments like radiation and chemotherapy. Reliable, simple, high throughput assays that measure the levels of mitochondrial energy metabolism in cells are useful determinants of treatment effects. Mitochondrial metabolism is routinely determined by measuring the rate of oxygen consumption (OCR). We have previously shown that indirect inhibition of plasma membrane electron transport (PMET) by the mitochondrial uncoupler, FCCP, may also be a reliable measure of mitochondrial energy metabolism. Here, we aimed to validate these earlier findings by exploring the relationship between stimulation of oxygen consumption by FCCP and inhibition of PMET.

Methods

We measured PMET by reduction of the cell impermeable tetrazolium salt WST-1/PMS. We characterised the effect of different growth conditions on the extent of PMET inhibition by FCCP. Next, we compared FCCP-mediated PMET inhibition with FCCP-mediated stimulation of OCR using the Seahorse XF96e flux analyser, in a panel of cancer cell lines.

Results

We found a strong inverse correlation between stimulation of OCR and PMET inhibition by FCCP. PMET and OCR were much more severely affected by FCCP in cells that rely on mitochondrial energy production than in cells with a more glycolytic phenotype.

Conclusion

Indirect inhibition of PMET by FCCP is a reliable, simple and inexpensive high throughput assay to determine the level of mitochondrial energy metabolism in cancer cells.

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WST-1/PMS dye reduction measures NADH-driven plasma membrane electron transport.

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FCCP stimulates mitochondrial oxygen consumption and inhibits dye reduction.

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The FCCP effect on dye reduction and oxygen consumption is inversely correlated.

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FCCP-mediated inhibition of dye reduction is a measure of mitochondrial metabolism.

Thiol switches in membrane proteins - Extracellular redox regulation in cell biology

Redox-mediated signal transduction depends on the enzymatic production of second messengers such as hydrogen peroxide, nitric oxide and hydrogen sulfite, as well as specific, reversible redox modifications of cysteine-residues in proteins. So-called thiol switches induce for instance conformational changes in specific proteins that regulate cellular pathways e.g., cell metabolism, proliferation, migration, gene expression and inflammation. Reduction, oxidation and disulfide isomerization are controlled by oxidoreductases of the thioredoxin family, including thioredoxins, glutaredoxins, peroxiredoxins and protein dsisulfide isomerases. These proteins are located in different cellular compartments, interact with substrates and catalyze specific reactions. Interestingly, some of these proteins are released by cells. Their extracellular functions and generally extracellular redox control have been widely underestimated. Here, we give an insight into extracellular redox signaling, extracellular thiol switches and their regulation by secreted oxidoreductases and thiol-isomerases, a topic whose importance has been scarcely studied so far, likely due to methodological limitations. We focus on the secreted redox proteins and characterized thiol switches in the ectodomains of membrane proteins, such as integrins and the metalloprotease ADAM17, which are among the best-characterized proteins and discuss their underlying mechanisms and biological implications.

Characterization of Transplasma Membrane Electron Transport Chain in Wild and Drug-Resistant Leishmania donovani Promastigote and Amastigote

BACKGROUND

Leishmania donovani (L. donovani) is one of the parasites that cause leishmaniasis. The mechanisms by which L. donovani fights against adverse environment and becomes resistant to drugs are not well understood yet.

OBJECTIVE

The present study was designed to evaluate the effects of different regulators on the modulation of Transplasma Membrane Electron Transport (transPMET) systems of susceptible and resistant L. donovani cells.

MATERIALS AND METHODS

Effects of UV, different buffers, and electron transport inhibitors and stimulators on the reduction of α-lipoic acid (ALA), 1,2-naphthoquinone-4-sulphonic acid (NQSA) and ferricyanide were determined.

RESULTS AND DISCUSSION

ALA reductions were inhibited in susceptible, sodium antimony gluconate (SAG)-resistant and paromomycin (PMM)-resistant AG83 amastigote cells, and stimulated in susceptible and SAG-resistant AG83 promastigote cells upon UV exposure. The results indicate that UV irradiation almost oppositely affect ALA reductions in amastigotes and promastigotes. ALA reductions were stimulated in sensitive and inhibited in resistant GE1 amastigotes upon UV exposure. Susceptible amastigotes and promastigotes inhibited, and resistant amastigotes and promastigotes stimulated NQSA reduction under UV irradiation. Thus, susceptible and drug-resistant amastigotes and promastigotes are different in the reduction of ALA. Susceptible and resistant AG83 amastigotes and promastigotes inhibited the ferricyanide reductions upon UV exposure, which indicates, there is no such difference in ferricyanide reductions among susceptible as well as resistant AG83 amastigotes and promastigotes. The reductions of extracellular electron excerptors in susceptible promastigotes requires the availability of Na⁺ and Cl^- ions for maximal activity but susceptible amastigotes are mostly not dependent on the availability of Na⁺ and Cl^- ions. Both in promastigotes and amastigotes, reductions of electron acceptors were strongly inhibited by carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone. Furthermore, antimycin A, rotenone and capsaicin markedly inhibited the reductions of electron acceptors in promastigotes, but not in amastigotes.

CONCLUSION

Results of this study suggest that the transPMET system is functionally different in wild and resistant strains of L. donovani.

Plasma membrane redox enzymes: new therapeutic targets for neurodegenerative diseases

Mitochondrial dysfunction caused by oxidative stress appears at early stages of aging and age-related diseases. Plasma membrane redox enzymes act in a compensatory manner to decrease oxidative stress and supply reductive capacity to ensure cell survival. Plasma membrane redox enzymes transfer electrons from NAD(P)H to oxidized ubiquinone and α-tocopherol, resulting in inhibition of further oxidative damage. Plasma membrane redox enzymes and their partners are affected by aging, leading to progression of neurodegenerative disease pathogenesis. Up-regulating plasma membrane redox enzymes via calorie restriction and phytochemicals make cells more resistant to oxidative damage under stress conditions by maintaining redox homeostasis and improving mitochondrial function. Investigation into plasma membrane redox enzymes can provide mechanistic details underlying the relationships between plasma membrane redox enzymes and mitochondrial complexes and provide a good therapeutic target for prevention and delay of neurodegenerative disorders.

New Perspectives on Iron Uptake in Eukaryotes

All eukaryotic organisms require iron to function. Malfunctions within iron homeostasis have a range of physiological consequences, and can lead to the development of pathological conditions that can result in an excess of non-transferrin bound iron (NTBI). Despite extensive understanding of iron homeostasis, the links between the “macroscopic” transport of iron across biological barriers (cellular membranes) and the chemistry of redox changes that drive these processes still needs elucidating. This review draws conclusions from the current literature, and describes some of the underlying biophysical and biochemical processes that occur in iron homeostasis. By first taking a broad view of iron uptake within the gut and subsequent delivery to tissues, in addition to describing the transferrin and non-transferrin mediated components of these processes, we provide a base of knowledge from which we further explore NTBI uptake. We provide concise up-to-date information of the transplasma electron transport systems (tPMETSs) involved within NTBI uptake, and highlight how these systems are not only involved within NTBI uptake for detoxification but also may play a role within the reduction of metabolic stress through regeneration of intracellular NAD(P)H/NAD(P)⁺ levels. Furthermore, we illuminate the thermodynamics that governs iron transport, namely the redox potential cascade and electrochemical behavior of key components of the electron transport systems that facilitate the movement of electrons across the plasma membrane to the extracellular compartment. We also take account of kinetic changes that occur to transport iron into the cell, namely membrane dipole change and their consequent effects within membrane structure that act to facilitate transport of ions.

Comparative profiling of microRNAs and their effects on abiotic stress in wild-type and dark green leaf color mutant plants of Anthurium andraeanum 'Sonate'

MicroRNAs (miRNAs) are a class of non-coding small RNAs that play important roles in the regulation of gene expression. Although plant miRNAs have been extensively studied in model systems, less is known in other plants with limited genome sequence data, including Anthurium andraeanum. To identify miRNAs and their target genes in A. andraeanum and study their responses to abiotic stresses, we conducted deep-sequencing of two small RNA (sRNA) libraries prepared from young leaves of wild-type (WT) and dark green (dg) leaf color mutant plants of A. andraeanum 'Sonate'. A total of 53 novel miRNAs were identified, 32 of which have been annotated to 18 miRNA families. 10 putative miRNAs were found to be differentially expressed in WT and dg, among which two miRNAs were significantly up-regulated and eight down-regulated in dg relative to WT. One differentially expressed miRNA, Aa-miR408, was dramatically up-regulated in dg. qRT-PCR analysis and heterologous expression of Aa-miR408 in Arabidopsis under different stress treatments suggest that Aa-miR408 is involved in abiotic stress responses in A. andraeanum. Our results provide a foundation for further dissecting the roles of miRNAs and their targets in regulating abiotic stress tolerance in A. andraeanum.

The teleos of metallo-reduction and metallo-oxidation in eukaryotic iron and copper trafficking

Eukaryotic cells, whether free-living or organismal, rely on metallo-reductases to process environmental ferric iron and cupric copper prior to uptake. In addition, some free-living eukaryotes (e.g. fungi and algae) couple ferri-reduction to ferro-oxidation, a process catalyzed by a small cohort of multi-copper oxidases; in these organisms, the ferric iron product is a ligand for cell iron uptake via a ferric iron permease. In addition to their support of iron uptake in lower eukaryotes, ferroxidases support ferrous iron efflux in Chordata; in this process the release of the ferrous iron from the efflux transporter is catalyzed by its ferroxidation. Last, ferroxidases also catalyze the oxidation of cuprous copper and, as metallo-oxidases, mirror the dual activity of the metallo-reductases. This Perspective examines the teleos of the yin-yang of this redox cycling of iron and copper in their metabolism.

Trans-Plasma Membrane Electron Transport and Ascorbate Efflux by Skeletal Muscle

Trans-plasma membrane electron transport (tPMET) and the antioxidant roles of ascorbate reportedly play a role in protection of cells from damage by reactive oxygen species, which have been implicated in causing metabolic dysfunction such as insulin resistance. Skeletal muscle comprises the largest whole-body organ fraction suggesting a potential role of tPMET and ascorbate export as a major source of extracellular antioxidant. We hypothesized that skeletal muscle is capable of tPMET and ascorbate efflux. To measure these processes, we assayed the ability of cultured muscle cells, satellite cells, and isolated extensor digitorum longus (EDL) and soleus (SOL) to reduce two extracellular electron acceptors, water soluble tetrazolium salt 1 (WST-1), and dichlorophenolindophenol (DPIP). Ascorbate oxidase (AO) was utilized to determine which portion of WST-1 reduction was dependent on ascorbate efflux. We found that muscle cells can reduce extracellular electron acceptors. In C2C12 myotubes and satellite cells, a substantial portion of this reduction was dependent on ascorbate. In myotubes, glucose transporter 1 (GLUT1) inhibitors along with a pan-GLUT inhibitor suppressed tPMET and ascorbate efflux, while a GLUT4 inhibitor had no effect. The adenosine 5′-monophosphate (AMP)-activated protein kinase activator 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) suppressed both tPMET and ascorbate efflux by myotubes, while insulin had no effect. Taken together, our data suggest that muscle cells are capable of tPMET and ascorbate efflux supported by GLUT1, thus illustrating a model in which resting muscle exports electrons and antioxidant to the extracellular environment.

Red wine activates plasma membrane redox system in human erythrocytes

In the present study, we report that polyphenols present in red wine obtained by a controlled microvinification process are able to protect human erythrocytes from oxidative stress and to activate Plasma Membrane Redox System (PMRS). Human plasma obtained from healthy subjects was incubated in the presence of whole red wine at a concentration corresponding to 9.13-73 μg/ml gallic acid equivalents to verify the capacity to protect against hypochlorous acid (HOCl)-induced plasma oxidation and to minimize chloramine formation. Red wine reduced hemolysis and chloramine formation induced by HOCl of 40 and 35%, respectively. PMRS present on human erythrocytes transfers electrons from intracellular molecules to extracellular electron acceptors. We demonstrated that whole red wine activated PMRS activity in human erythrocytes isolated from donors in a dose-dependent manner with a maximum at about 70-100 μg/ml gallic acid equivalents. We also showed that red wine increased glutathione (GSH) levels and erythrocytic antioxidant capacity, measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH) quenching assay. Furthermore, we reported that GSH played a crucial role in regulating PMRS activity in erythrocytes. In fact, the effect of iodoacetamide, an alkylating agent that induces depletion of intracellular GSH, was completely counteracted by red wine. Bioactive compounds present in red wine, such as gallic acid, resveratrol, catechin, and quercetin were unable to activate PMRS when tested at the concentrations normally present in aged red wines. On the contrary, the increase of PMRS activity was associated with the anthocyanin fraction, suggesting the capacity of this class of compounds to positively modulate PMRS enzymatic activity.

Modulation of Erythrocyte Plasma Membrane Redox System Activity by Curcumin

Plasma membrane redox system (PMRS) is an electron transport chain system ubiquitously present throughout all cell types. It transfers electron from intracellular substrates to extracellular acceptors for regulation of redox status. Curcumin, isolated from Curcuma longa, has modulatory effects on cellular physiology due to its membrane interaction ability and antioxidant potential. The present study investigates the effect of curcumin on PMRS activity of erythrocytes isolated from Wistar rats in vitro and in vivo and validated through an in silico docking simulation study using Molegro Virtual Docker (MVD). Effects of curcumin were also evaluated on level of glutathione (GSH) and the oxidant potential of plasma measured in terms of plasma ferric equivalent oxidative potentials (PFEOP). Results show that curcumin significantly (p < 0.01) downregulated the PMRS activity in a dose-dependent manner. Molecular docking results suggest that curcumin interacts with amino acids at the active site cavity of cytochrome b 5 reductase, a key constituent of PMRS. Curcumin also increased the GSH level in erythrocytes and plasma while simultaneously decreasing the oxidant potential (PFEOP) of plasma. Altered PMRS activity and redox status are associated with the pathophysiology of several health complications including aging and diabetes; hence, the above finding may explain part of the role of curcumin in health beneficial effects.

Redox regulation of ion channels in the pulmonary circulation

SIGNIFICANCE

The pulmonary circulation is a low-pressure, low-resistance, highly compliant vasculature. In contrast to the systemic circulation, it is not primarily regulated by a central nervous control mechanism. The regulation of resting membrane potential due to ion channels is of integral importance in the physiology and pathophysiology of the pulmonary vasculature.

RECENT ADVANCES

Redox-driven ion conductance changes initiated by direct oxidation, nitration, and S-nitrosylation of the cysteine thiols and indirect phosphorylation of the threonine and serine residues directly affect pulmonary vascular tone.

CRITICAL ISSUES

Molecular mechanisms of changes in ion channel conductance, especially the identification of the sites of action, are still not fully elucidated.

FUTURE DIRECTIONS

Further investigation of the interaction between redox status and ion channel gating, especially the physiological significance of S-glutathionylation and S-nitrosylation, could result in a better understanding of the physiological and pathophysiological importance of these mediators in general and the implications of such modifications in cellular functions and related diseases and their importance for targeted treatment strategies.

Mammalian iron homeostasis in health and disease: uptake, storage, transport, and molecular mechanisms of action

Iron is a crucial factor for life. However, it also has the potential to cause the formation of noxious free radicals. These double-edged sword characteristics demand a tight regulation of cellular iron metabolism. In this review, we discuss the various pathways of cellular iron uptake, cellular iron storage, and transport. Recent advances in understanding the reduction and uptake of non-transferrin-bound iron are discussed. We also discuss the recent progress in the understanding of transcriptional and translational regulation by iron. Furthermore, we discuss recent advances in the understanding of the regulation of cellular and systemic iron homeostasis and several key diseases resulting from iron deficiency and overload. We also discuss the knockout mice available for studying iron metabolism and the related human conditions.

In vivo inhibition of trans-plasma membrane electron transport by antiviral drugs in grapevine

Electrophysiological techniques were applied to investigate the action of antiviral drugs during trans-plasma events in in vivo grapevine cells infected by GLRaV-1 and GLRaV-3. Carbon fiber microelectrodes and redox-sensitive dyes were used to measure trans-plasma membrane electron transport (t-PMET) activity in healthy and infected samples treated with ribavirin, tiazofurin and oseltamivir. Each drug caused a reduction in oxidation current (expressed as Δ[Fe(2+)]) in healthy samples, indicating t-PMET inhibition. In almost all infected samples, the effect of drugs on t-PMET activity was significantly lower, suggesting that higher content of NADH in infected plants can interfere with t-PMET inhibition caused by drugs. Moreover, virus-infected samples exhibited elevated t-PMET activity compared to healthy samples. Analogous effects were observed by dye tests. Considering the effects of drugs on trans-plasma membrane potential, tests showed the activity of a proton pump during drug treatments with no significant difference with regard to health status.

Monocyte-macrophage membrane possesses free radicals scavenging activity: stimulation by polyphenols or by paraoxonase 1 (PON1)

In the current study, we analysed free radicals scavenging activity of monocytes-macrophages in the absence or presence of antioxidants such as polyphenols or paraoxonase 1 (PON1). THP-1 human monocytic cell line, murine J774A.1 macrophages, as well as human primary monocytes have the capability to scavenge free radicals, as measured by the 1-diphenyl-2-picryl-hydrazyl (DPPH) assay. This effect (which could be attributed to the cell's membrane) was cell number and incubation time dependent. Upon incubation of J774A.1 macrophages with acetylated LDL (Ac-LDL), with VLDL, or with the radical generator, AAPH, the cells' lipid peroxides content, and paraoxonase 2 (PON2) activity were significantly increased. While non-treated cells decreased DPPH absorbance by 65%, the Ac-LDL-, VLDL- or AAPH-treated cells, decreased it by only 33%, 30%, or 45%, respectively. We next analysed the effect of J774A.1 macrophage enrichment with antioxidants, such as polyphenols or PON1 on the cells' free radicals scavenging activity. Non-treated cells decreased DPPH absorbance by 50%, whereas vitamin E-, punicalagin- or PJ-treated cells significantly further decreased it, by 75%. Similarly, in PON1-treated cells DPPH absorbance was further decreased by 63%, in association with 23% increment in PON1 catalytic activity. In cells under oxidative stress [treated with AAPH-, or with oxidized LDL], PON1 activity was decreased by 31% or 40%, as compared to the activity observed in PON1 incubated with non-treated cells. We conclude that monocytes-macrophages possess free radicals scavenging activity, which is decreased under atherogenic conditions, and increased upon cell enrichment with potent antioxidants such as nutritional polyphenols, or PON1.

Effect of mycophenolic acid on trans-plasma membrane electron transport and electric potential in virus-infected plant tissue

Mycophenolic acid (MPA) is an inosine monophosphate dehydrogenase inhibitor whose antiviral mechanism of action is supposed to interfere with NAD(+)/NADH conversion. Its effects on trans-plasma membrane electron transport (t-PMET) and on trans-plasma membrane electric potential (t-PMEP), which are involved in the NAD(+)/NADH conversion, were investigated using microelectrochemical techniques in tobacco plants infected by Cucumber mosaic virus. In these tests, ferricyanide (Fe(3+)) was used as electron acceptor in assays performed with intact cells; ferricyanide is converted to ferrocyanide (Fe(2+)) by one-electron reduction, and the rate of this reduction can be monitored in order to investigate the effects on t-PMET or t-PMEP. Considering tests on t-PMEP, MPA treatment of samples induced membrane depolarization and this effect was greater in healthy samples compared to infected ones. In any case, complete repolarization was achieved, indicating no irreversible damage to the membrane due to MPA administration. Moreover, in samples pre-treated with MPA, the extent of depolarization caused by Fe(3+) administration was lower than in samples without pre-treatment but the MPA effect was not related to virus infection. With regard to tests on t-PMET, MPA caused a reduction in Fe(3+)/Fe(2+) conversion compared to untreated plants. However, infected samples were less sensitive to MPA treatment, which may be due to the concurrent entry of MPA within the symplast that, as indicated by t-PMEP tests, was lower in infected samples. In conclusion, MPA interferes with membrane activity linked to NAD(+)/NADH conversion, acting differently in infected or healthy samples during drug uptake by cells.

Mitochondrial genome-knockout cells demonstrate a dual mechanism of action for the electron transport complex I inhibitor mycothiazole

Mycothiazole, a polyketide metabolite isolated from the marine sponge Cacospongia mycofijiensis, is a potent inhibitor of metabolic activity and mitochondrial electron transport chain complex I in sensitive cells, but other cells are relatively insensitive to the drug. Sensitive cell lines (IC(50) 0.36-13.8 nM) include HeLa, P815, RAW 264.7, MDCK, HeLa S3, 143B, 4T1, B16, and CD4/CD8 T cells. Insensitive cell lines (IC(50) 12.2-26.5 μM) include HL-60, LN18, and Jurkat. Thus, there is a 34,000-fold difference in sensitivity between HeLa and HL-60 cells. Some sensitive cell lines show a biphasic response, suggesting more than one mechanism of action. Mitochondrial genome-knockout ρ(0) cell lines are insensitive to mycothiazole, supporting a conditional mitochondrial site of action. Mycothiazole is cytostatic rather than cytotoxic in sensitive cells, has a long lag period of about 12 h, and unlike the complex I inhibitor, rotenone, does not cause G(2)/M cell cycle arrest. Mycothiazole decreases, rather than increases the levels of reactive oxygen species after 24 h. It is concluded that the cytostatic inhibitory effects of mycothiazole on mitochondrial electron transport function in sensitive cell lines may depend on a pre-activation step that is absent in insensitive cell lines with intact mitochondria, and that a second lower-affinity cytotoxic target may also be involved in the metabolic and growth inhibition of cells.

Plant polyphenols as electron donors for erythrocyte plasma membrane redox system: validation through in silico approach

Background

The plasma membrane redox system (PMRS) has extensively been studied in erythrocytes. The PMRS plays an important role in maintaining plasma redox balance and provides a protective mechanism against oxidative stress. Earlier it was proposed that only NADH or NADPH provided reducing equivalents to PMRS; however, now it is acknowledged that some polyphenols also have the ability to donate reducing equivalents to PMRS.

Methods

Two different docking simulation softwares, Molegro Virtual Docker and Glide were used to study the interaction of certain plant polyphenols viz. quercetin, epigallocatechin gallate, catechin epicatechin and resveratrol with human erythroyte NADH-cytochrome b5 reductase, which is a component of PMRS and together with the identification of minimum pharmacophoric feature using Pharmagist.

Results

The derived common minimum pharmacophoric features show the presence of minimum bioactive component in all the selected polyphenols. Our results confirm wet lab findings which show that these polyphenols have the ability to interact and donate protons to the Human NADH-cytochrome b5 reductase.

Conclusion

With the help of these comparative results of docking simulation and pharmacophoric features, novel potent molecules can be designed with higher efficacy for activation of the PMRS system.

Trans-plasma membrane electron transport in mammals: functional significance in health and disease

Trans-plasma membrane electron transport (t-PMET) has been established since the 1960s, but it has only been subject to more intensive research in the last decade. The discovery and characterization at the molecular level of its novel components has increased our understanding of how t-PMET regulates distinct cellular functions. This review will give an update on t-PMET, with particular emphasis on how its malfunction relates to some diseases, such as cancer, abnormal cell death, cardiovascular diseases, aging, obesity, neurodegenerative diseases, pulmonary fibrosis, asthma, and genetically linked pathologies. Understanding these relationships may provide novel therapeutic approaches for pathologies associated with unbalanced redox state.

Redox modulation of Ecto-NOX1 in human platelets

By modulating the cellular redox state, the plasma membrane electron transport (PMET) is important in platelet biology; indeed, the oxidant/antioxidant balance plays a central role during activation of the coagulation pathway. None the less, in human platelets, the PMET system has not yet been fully characterized and the molecular identities of most components are unknown. Here, for the first time, the presence of the plasma membrane hydroquinone (NADH) oxidase Ecto-NOX1 in human platelets has been described. We found that Ecto-NOX1 expression is modulated by capsaicin: Indeed, it is positively regulated through a mechanism requiring binding of capsaicin to its receptor, namely the transient receptor potential vanilloid subtype 1 (TRPV1). Ligand-receptor interaction triggers a signalling cascade leading to ROS production, which in turn enhances expression and activity of Ecto-NOX1. Redox regulation of Ecto-NOX1 may be important to platelet recruitment and activation during inflammatory diseases.

Nrf2 signaling, a mechanism for cellular stress resistance in long-lived mice

Transcriptional regulation of the antioxidant response element (ARE) by Nrf2 is important for the cellular adaptive response to toxic insults. New data show that primary skin-derived fibroblasts from the long-lived Snell dwarf mutant mouse, previously shown to be resistant to many toxic stresses, have elevated levels of Nrf2 and of multiple Nrf2-sensitive ARE genes. Dwarf-derived fibroblasts exhibit many of the traits associated with enhanced activity of Nrf2/ARE, including higher levels of glutathione and resistance to plasma membrane lipid peroxidation. Treatment of control cells with arsenite, an inducer of Nrf2 activity, increases their resistance to paraquat, hydrogen peroxide, cadmium, and UV light, rendering these cells as stress resistant as untreated cells from dwarf mice. Furthermore, mRNA levels for some Nrf2-sensitive genes are elevated in at least some tissues of Snell dwarf mice, suggesting that the phenotypes observed in culture may be mirrored in vivo. Augmented activity of Nrf2 and ARE-responsive genes may coordinate many of the stress resistance traits seen in cells from these long-lived mutant mice.

A novel biofuel cell harvesting energy from activated human macrophages

Macrophage phagocytosis activates NADPH oxidase, an electron transport system in the plasma membrane. This study examined the feasibility of utilizing electrons transferred through the plasma membrane via NADPH oxidase to run a biofuel cell. THP-1 human monocytic cells were chemically stimulated to differentiate into macrophages. Further they were activated to induce a phagocytic response. During differentiation, cells became adherent to a plain gold electrode which was used as anode in a two-compartment fuel cell system. The current production in the fuel cell always corresponded to the NADPH oxidase activity, which was evaluated by the amount of superoxide anion produced upon stimulation in combination with the expression levels of the different NADPH oxidase subunits in cells. Moreover, our results of different inhibitory tests let us conclude that (i) the current observed in the fuel cell originates from NADPH oxidase in activated macrophages and (ii) there are multiple electron transport pathways from the cells to the electrode. One pathway involves superoxide anions produced upon stimulation, additional not yet identified electron transport occurs independently of superoxide anions.This type of novel biofuel cell driven by living human cells may eventually develop into a battery replacement for small medical devices.

Age-associated changes in synaptic lipid raft proteins revealed by two-dimensional fluorescence difference gel electrophoresis

Brain aging is associated with a progressive decline in cognitive function though the molecular mechanisms remain unknown. Functional changes in brain neurons could be due to age-related alterations in levels of specific proteins critical for information processing. Specialized membrane microdomains known as 'lipid rafts' contain protein complexes involved in many signal transduction processes. This study was undertaken to determine if two-dimensional fluorescence difference gel electrophoresis (2D DIGE) analysis of proteins in synaptic membrane lipid rafts revealed age-dependent alterations in levels of raft proteins. Five pairs of young and aged rat synaptic membrane rafts were subjected to DIGE separation, followed by image analysis and identification of significantly altered proteins. Of 1046 matched spots on DIGE gels, 94 showed statistically significant differences in levels between old and young rafts, and 87 of these were decreased in aged rafts. The 41 most significantly altered (p<0.03) proteins included several synaptic proteins involved in energy metabolism, redox homeostasis, and cytoskeletal structure. This may indicate a disruption in bioenergetic balance and redox homeostasis in synaptic rafts with brain aging. Differential levels of representative identified proteins were confirmed by immunoblot analysis. Our findings provide novel pathways in investigations of mechanisms that may contribute to altered neuronal function in aging brain.

An investigation of hemopexin redox properties by spectroelectrochemistry: biological relevance for heme uptake

Hemopexin (HPX) has two principal roles: it sequesters free heme in vivo for the purpose of preventing the toxic effects of this moiety, which is largely due to heme's ability to catalyze free radical formation, and it transports heme intracellularly thus limiting its availability as an iron source for pathogens. Spectroelectrochemistry was used to determine the redox potential for heme and meso-heme (mH) when bound by HPX. At pH 7.2, the heme-HPX assembly exhibits E (1/2) values in the range 45-90 mV and the mH-HPX assembly in the range 5-55 mV, depending on environmental electrolyte identity. The E (1/2) value exhibits a 100 mV positive shift with a change in pH from 7.2 to 5.5 for mH-HPX, suggesting a single proton dependent equilibrium. The E (1/2) values for heme-HPX are more positive in the presence of NaCl than KCl indicating that Na(+), as well as low pH (5.5) stabilizes ferro-heme-HPX. Furthermore, comparing KCl with K(2)HPO(4), the chloride salt containing system has a lower potential, indicating that heme-HPX is easier to oxidize. These physical properties related to ferri-/ferro-heme reduction are both structurally and biologically relevant for heme release from HPX for transport and regulation of heme oxygenase expression. Consistent with this, when the acidification of endosomes is prevented by bafilomycin then heme oxygenase-1 induction by heme-HPX no longer occurs.

The antiproliferative effects of phenoxodiol are associated with inhibition of plasma membrane electron transport in tumour cell lines and primary immune cells

Although the redox-active synthetic isoflavene, phenoxodiol, is in Phase 3 clinical trials for drug-resistant ovarian cancer, and in early stage clinical trials for prostate and cervical cancer, its primary molecular target is unknown. Nevertheless, phenoxodiol inhibits proliferation of many cancer cell lines and induces apoptosis by disrupting FLICE-inhibitory protein, FLIP, expression and by caspase-dependent and -independent degradation of the X-linked inhibitor of apoptosis, XIAP. In addition, phenoxodiol sensitizes drug-resistant tumour cells to anticancer drugs including paclitaxel, carboplatin and gemcitabine. Here, we investigate the effects of phenoxodiol on plasma membrane electron transport (PMET) and cell proliferation in human leukemic HL60 cells and mitochondrial gene knockout HL60rho(o) cells that exhibit elevated PMET. Phenoxodiol inhibited PMET by both HL60 (IC(50) 32 microM) and HL60rho(o) (IC(50) 70 microM) cells, and this was associated with inhibition of cell proliferation (IC(50) of 2.8 and 6.7 microM, respectively), pan-caspase activation and apoptosis. Unexpectedly, phenoxodiol also inhibited PMET by activated murine splenic T cells (IC(50) of 29 microM) as well as T cell proliferation (IC(50) of 2.5 microM). In contrast, proliferation of WI-38 cells and HUVECs was only weakly affected by phenoxodiol. These results indicate that PMET may be a primary target for phenoxodiol in tumour cells and in activated T cells.

Erythrocyte transmembrane electron transfer in haemodialysis patients

BACKGROUND AND AIMS

Patients with chronic renal failure, especially those treated with haemodialysis, have an increased risk of developing atherosclerotic vascular disease probably as a result of enhanced oxidative stress. The human cell membrane possesses electron transfer systems which protect against extracellular pro-oxidant challenge. We evaluated (1) the erythrocyte velocity of ferricyanide reduction (RBC vfcy) in 25 uraemic patients (aged 25-71 years; 14 males), (2) the changes induced by a single haemodialysis session and (3) biomarkers of oxidative stress.

METHODS AND RESULTS

Before and after a mid-week dialysis session, we measured RBC vfcy, erythrocyte glutathione (RBC GSH), plasma and red cell membrane malondialdehyde (P and RBC MDA), plasma sulphydryl groups (P SH), plasma vitamin C levels and haemolysis percentage. Pre-dialysis RBC GSH (0.68+/-0.13 vs 0.80+/-0.13 mg/mL, p<0.01), P SH (266+/-74 vs 406+/-78 micromol/L, p<0.01) and plasma vitamin C (7.0+/-5.1 vs 21.5+/-8.5mg/L, p<0.001) were lower than in 25 age-sex-matched healthy controls; P MDA (1.57+/-0.52 vs 0.54+/-0.29 nmol/mL, p<0.001), RBC MDA (0.42+/-0.13 vs 0.34+/-0.16 nmol/mL, p<0.05) and haemolysis (1.2+/-0.3 vs 0.7+/-0.3%, p<0.001) were increased. Baseline RBC vfcy did not differ from normals (13.1+/-5.2 vs 12.9+/-3.2 mmol/mL/h). Following dialysis, RBC vfcy (to 8.9+/-4.5 mmol/mL/h, p<0.001) decreased, as well as P MDA, RBC MDA and plasma vitamin C (to 2.5+/-1.4 mg/L, p<0.001), whereas P SH groups increased (to 413+/-99 micromol/L, p<0.001); haemolysis percentage remained high. RBC vfcy values were correlated to RBC GSH and vitamin C levels.

CONCLUSIONS

Uraemic patients showed signs of oxidative stress. Pre-dialysis RBC vfcy is maintained in the normal range on account of a reduced intracellular content of GSH and in spite of low plasma ascorbate. A single haemodialysis treatment reduced biomarkers of protein and lipid oxidation but markedly impaired transmembrane electron transfer, which could be explained by acute depletion of electron donors.

Up-regulation of plasma membrane-associated redox activities in neuronal cells lacking functional mitochondria

Mitochondria-deficient cells (rho(o) cells) survive through enhanced glycolytic metabolism in the presence of pyruvate and uridine. The plasma membrane redox system (PMRS) contains several NAD(P)H-related enzymes and plays a key role in maintaining the levels of NAD(+)/NADH and reduced coenzyme Q. In this study, rho(o) cells were used to investigate how the PMRS is regulated under conditions of mitochondrial dysfunction. rho(o) cells exhibited a lower oxygen consumption rate and higher levels of lactate than parental cells, and were more sensitive to glycolysis inhibitors (2-deoxyglucose and iodoacetamide) than control cells. However, they were more resistant to H(2)O(2), consistent with increased catalase activity and decreased oxidative damage (protein carbonyls and nitrotyrosine). PM-associated redox enzyme activities were enhanced in rho(o) cells compared to those in control cells. Our data suggest that all PMRS enzymes and biomarkers tested are closely related to the ability of the PMs to maintain redox homeostasis. These results illustrate that an up-regulated PM redox activity can protect cells from oxidative stress as a result of an improved antioxidant capacity, and suggest a mechanism by which neurons adapt to conditions of impaired mitochondrial function.

Calorie restriction up-regulates the plasma membrane redox system in brain cells and suppresses oxidative stress during aging

The plasma membrane (PM) contains redox enzymes that provide electrons for energy metabolism and recycling of antioxidants such as coenzyme Q and alpha-tocopherol. Brain aging and neurodegenerative disorders involve impaired energy metabolism and oxidative damage, but the involvement of the PM redox system (PMRS) in these processes is unknown. Caloric restriction (CR), a manipulation that protects the brain against aging and disease, increased activities of PMRS enzymes (NADH-ascorbate free radical reductase, NADH-quinone oxidoreductase 1, NADH-ferrocyanide reductase, NADH-coenzyme Q10 reductase, and NADH-cytochrome c reductase) and antioxidant levels (alpha-tocopherol and coenzyme Q10) in brain PM during aging. Age-related increases in PM lipid peroxidation, protein carbonyls, and nitrotyrosine were attenuated by CR, levels of PMRS enzyme activities were higher, and markers of oxidative stress were lower in cultured neuronal cells treated with CR serum compared with those treated with ad libitum serum. These findings suggest important roles for the PMRS in protecting brain cells against age-related increases in oxidative and metabolic stress.

The plasma membrane redox system in aging

Oxidative stress over time leads to the accumulation of damaged macromolecules and to profound physiological changes that are associated with several age-related diseases. The plasma membrane redox system (PMRS) appears to attenuate oxidative stress acting as a compensatory mechanism during the aging process. The PMRS appears to play a protective role during mitochondrial dysfunction to provide cells with a survival mechanism by lowering oxidative stress. The PMRS accomplishes this by producing more NAD(+) for glycolytic ATP production via transfer of electrons from intracellular reducing equivalents to extracelluar acceptors. Ubiquinone and alpha-tocopherol are key antioxidant molecules in the plasma membrane that are affected by aging and can be up-regulated by dietary interventions such as calorie restriction (CR). Up-regulation of PMRS activity leads to cell survival and membrane homeostasis under stress conditions and during calorie restriction. Further studies of the PMRS may provide not only additional information on the mechanisms involved in aging and CR, but may provide therapeutic targets for the prevention and treatment of age-related diseases.

Redox enzymes in tethered membranes

An electrode surface is presented that enables the characterization of redox-active membrane enzymes in a native-like environment. An ubiquinol oxidase from Escherichia coli, cytochrome bo(3) (cbo(3)), has been co-immobilized into tethered bilayer lipid membranes (tBLMs). The tBLM is formed on gold surfaces functionalized with cholesterol tethers which insert into the lower leaflet of the membrane. The planar membrane architecture is formed by self-assembly of proteoliposomes, and its structure is characterized by surface plasmon resonance (SPR), electrochemical impedance spectroscopy (EIS), and tapping-mode atomic force microscopy (TM-AFM). The functionality of cbo(3) is investigated by cyclic voltammetry (CV) and is confirmed by the catalytic reduction of oxygen. Interfacial electron transfer to cbo(3) is mediated by the membrane-localized ubiquinol-8, the physiological electron donor of cbo(3). Enzyme coverages observed with TM-AFM and CV coincide (2-8.5 fmol.cm(-)(2)), indicating that most-if not all-cbo(3) on the surface is catalytically active and thus retains its integrity during immobilization.

Mitochondrial gene knockout HL60rho0 cells show preferential differentiation into monocytes/macrophages

This study compares the differentiation potential of mitochondrial gene knockout (rho0) and parental HL60 cells in response to 1.25% dimethylsulfoxide (DMSO) and 10nM phorbol myristate acetate (PMA). Compared to HL60 cells, undifferentiated HL60rho0 cells showed partial monocyte/macrophage differentiation, with increased CD11c and CD14 expression, decreased CD71 expression, and weak non-specific esterase staining. Differentiation along the monocyte/macrophage pathway (PMA) was more pronounced in HL60rho0 than parental HL60 cells with increased CD11c and CD14 expression and stronger non-specific esterase staining. DMSO-exposure resulted in a poorly differentiated nuclear morphology, small respiratory burst and marginal up-regulation of CD15 expression in HL60rho0 cells.

Azo reductase activity of intact saccharomyces cerevisiae cells is dependent on the Fre1p component of plasma membrane ferric reductase

Unspecific bacterial reduction of azo dyes is a process widely studied in correlation with the biological treatment of colored wastewaters, but the enzyme system associated with this bacterial capability has never been positively identified. Several ascomycete yeast strains display similar decolorizing behaviors. The yeast-mediated process requires an alternative carbon and energy source and is independent of previous exposure to the dyes. When substrate dyes are polar, their reduction is extracellular, strongly suggesting the involvement of an externally directed plasma membrane redox system. The present work demonstrates that, in Saccharomyces cerevisiae, the ferric reductase system participates in the extracellular reduction of azo dyes. The S. cerevisiae Deltafre1 and Deltafre1 Deltafre2 mutant strains, but not the Deltafre2 strain, showed much-reduced decolorizing capabilities. The FRE1 gene complemented the phenotype of S. cerevisiae Deltafre1 cells, restoring the ability to grow in medium without externally added iron and to decolorize the dye, following a pattern similar to the one observed in the wild-type strain. These results suggest that under the conditions tested, Fre1p is a major component of the azo reductase activity.

Multiple proteins with single activities or a single protein with multiple activities: the conundrum of cell surface NADH oxidoreductases

Reduction of the cell-impermeable tetrazolium salt WST-1 has been used to characterise two plasma membrane NADH oxidoreductase activities in human cells. The trans activity, measured with WST-1 and the intermediate electron acceptor mPMS, utilises reducing equivalents from intracellular sources, while the surface activity, measured with WST-1 and extracellular NADH, is independent of intracellular metabolism. Whether these two activities involve distinct proteins or are inherent to a single protein is unclear. In this work, we have attempted to address this question by examining the relationship between the trans and surface WST-1-reducing activities and a third well-characterised family of cell surface oxidases, the ECTO-NOX proteins. Using blue native-polyacrylamide gel electrophoresis, we have identified a complex in the plasma membranes of human 143B osteosarcoma cells responsible for the NADH-dependent reduction of WST-1. The dye-reducing activity of the 300 kDa complex was attributed to a 70 kDa NADH oxidoreductase activity that cross-reacted with antisera against the ECTO-NOX protein CNOX. Differences in enzyme activities and inhibitor profiles between the WST-1-reducing NADH oxidoreductase enzyme in the presence of NADH or mPMS and the ECTO-NOX family are reconciled in terms of the different purification methods and assay systems used to study these proteins.

Voltage-dependent anion-selective channel 1 (VDAC1)—a mitochondrial protein, rediscovered as a novel enzyme in the plasma membrane

The eukaryotic porin or voltage-dependent anion-selective channel (VDAC1) is a pore-forming protein discovered twenty five years ago in the mitochondrial outer membrane. Its gene in eukaryotes is known, but its tertiary structure has never been solved. Structure predictions highlight the presence of several amphipathic beta-strands possibly organised in a beta-barrel. VDAC1 has recently been described as being a NADH:ferricyanide reductase in the plasma membrane. There it affects the regulation of cell growth and death. Physiological cell death (apoptosis) has become a major research focus of biomedical research. Regulation of the enzyme will have impacts on cancer and autoimmune diseases (insufficient apoptosis) as well as neurodegenerative diseases (excessive apoptosis). VDAC1 in the plasma membrane establishes a novel level of apoptosis regulation putatively via its redox activity.

Redox Coupling to Microbial Respiration: an Evaluation of Secondary Mediators as Binary Mixtures with Ferricyanide

MICREDOX is a rapid microbial-based assay, which was originally developed at Lincoln Technology to monitor biochemical oxygen demand (BOD).[1] The assay is characterized by high levels of biocatalyst (microorganisms) and redox mediator; these facilitate a fast reaction in which the microbial oxidation of an organic substrate is coupled with the reduction of the mediator. Previous efforts toward optimizing this assay have principally been directed at the selection and performance of different bacterial strains, either singly[2] or as a consortium.[3] Here we report the effect of adding a second mediator to the assay by comparing the coulombic responses and the substrate stoichiometric conversion efficiencies. Escherichia coli and half-strength standard BOD substrate (75 mg glucose L−1, 75 mg glutamic acid L−1; GGA) were incubated for one hour at 37°C in the absence of oxygen with an excess of redox mediator, potassium hexacyanoferrate(iii) (HCF), either individually or as a binary mixture that included a secondary mediator. Secondary redox mediators investigated were p-benzoquinone (BQ), 2,6-dichlorophenolindophenol (DPIP), menadione (MD), neutral red (NR), N,N′-tetramethyl-1,4-phenylenediamine (N-TMPD), phenazine ethosulphate (PES), and 2,3,5,6-tetramethyl-1,4-phenylenediamine (TMPD). When HCF was supplemented with TMPD or PES the stoichiometric conversion efficiency for the oxidation of the GGA by E. coli increased, whereas when supplemented with N-TMPD, MD, DCIP, or BQ the conversion efficiency decreased. No effect was evident when NR was used as the supplement.