Redox Potential Of Medium Research Articles

In silico studies disclose the underlying link between binding affinity and redox potential in laccase isoforms

Laccases are copper-containing enzymes belonging to the family of multicopper oxidases (MCOs). All MCOs use molecular oxygen to oxidize a wide range of organic compounds by radical catalysis. One of the key fundamental properties of laccases is having high or low redox potentials depending on the active site organization. Several experimental studies have been done to rationalize the high and low redox potential laccases (LRPL), however, molecular understanding is still lacking. In this work, we explored the proteomic profile of laccases produced in the fungal cultures, specifically induced with lignocellulosic biomass such as rice straw. This study was undertaken to explain the differences in the high redox and low redox potential values of different laccases using in-silico approaches. Proteomic profiling and structural and sequence analysis revealed a low level of similarity among them. Docking analyses and molecular dynamics simulation analysis revealed that high redox potential laccases (HRPL) are having good binding affinity compared to low or medium redox potential laccases (MRPL). The stability of these complexes was further analyzed based on reactive distances, active site volume comparison and a number of tunnel formations that were observed to be significantly higher for HRPL. Our results indicate that the number of tunnel formations calculated from the simulation’s trajectories and available water molecules at the T3 site directly correlates with the laccases’ redox potentials. This study will be helpful and provide valuable inputs for the designing of new laccases to improve lignin degradation. Communicated by Ramaswamy H. Sarma

Supramolecular Polymerization Powered by Escherichia coli : Fabricating a Near-Infrared Photothermal Antibacterial Agent in Situ

Supramolecular Polymerization Powered by <i>Escherichia coli</i> : Fabricating a Near-Infrared Photothermal Antibacterial Agent in Situ

THE ADDITION OF ANTIOXIDANTS EVERY 12 HOUR TO THE CULTURE MEDIUM SIGNIFICANTLY INCREASES THE RATE OF TOTAL USABLE AND EXPANDED BLASTOCYSTS IN PATIENTS WITH ADVANCED MATERNAL AGE: A PROSPECTIVE STUDY OF 1520 SIBLING HUMAN OOCYTES

To explore whether the adjustment of the culture medium redox potential every 12 hours by the supplementation with antioxidants to a similar value found in follicular fluid of oocyte donors may improve the cumulative rates of usable and expanded blastocysts as assessed at day 5 and 6 of development.

Действие персульфатов на содержание каротиноидов в культурах дрожжей Rhodosporidium sphaerocarpum, R. diobovatum и Rhodotorula glutinis

The methods for increasing the isolation of carotenoids from yeast producer cultures have been compared. It was shown that the optimal procedure is microwave pretreatment (2450 GHz, 600 W, 40 s) with subsequent extraction of the target products with methanol. Additives of sodium persulfate or ammonium persulfate to aerated culture medium provided additional oxygen sources for the yeast and increased the medium redox potential. The introduction of persulfate led to a 1.3-fold increase in the content of colored carotenoids in the R. dubiovatum VKPM Y-305 biomass as compared to the control without persulfate. In the R. sphaerocarpum VKPM Y-1559 biomass, persulfate at concentrations of 0.15 g/L and 0.50 g/L increased the content of colored carotenoids by 1.3 and 1.4 times, respectively. The optimal persulfate concentent depends on the yeast growth phase and time of exposure to the compound. Higher persulfate concentrations resulted in increased redox potential and discoloration of carotenoids, though without yeast cell death. yeasts, carotenoids, medium redox potential, persulfate

Insights into correlation between hydrogen yield improvement and glycerol addition in photo-fermentation of Arundo donax L.

This study aimed to explore the correlation between hydrogen yield improvement of photo-fermentation of Arundo donax L. and glycerol addition. Different glycerol concentrations (g/L) (0, 10, 15, 20, and 30) were replenished to establish co-substrate system. And statistical analysis was introduced to evaluate the correlation. The maximum hydrogen yield improvement (294%) was obtained from glycerol addition of 15 g/L in comparison with mono-substrate system of Arundo donax L. Under the optimal glycerol addition (15 g/L), the glycerol/Arundo donax L. ratio, C/N ratio, initial medium redox potential (Eh), and solid/liquid ratio were 1:1, 25.1, 57 mV, and 1/68, respectively. In addition, canonical correlation analysis (CCA) indicated that initial and final medium redox potential (Eh) had the strongest relationship with yield improvement of photo-fermentation. Moreover, Pearson’s correlation analysis claimed that Arundo donax L./glycerol ratio played a key role during the photo-fermentative hydrogen production (PFHP) process.

High performance hybrid Mg-Li ion batteries with conversion cathodes for low cost energy storage

The recently proposed hybrid Mg-Li ion battery technology delivers good reaction kinetics and excellent safety features because it integrates the advantages of the Mg metal anode and the Li+ ion intercalation/conversion electrodes. The inexpensive and resource-abundant FeS is a suitable candidate as a cathode material due to its medium redox potential and high theoretical capacity; however, a conventional FeS cathode suffers from low electronic conductivity, low coulombic efficiency and poor cycling performance. Here, in this work, to overcome these drawbacks, a free-standing membrane electrode with FeS nanoparticles embedded in carbon nanofibers was designed and prepared via a facile electrospinning method. Additionally, because of the absence of inactive materials, such as the current collector and binder, the energy density was enhanced compared with that in the conventional batteries. The hybrid Mg-Li ion battery fabricated in this study can deliver a maximum energy density of ∼300 Wh kg−1, which is superior to that of most conventional Mg ion batteries. An outstanding cyclic performance for up to 800 cycles with high coulombic efficiencies above 97% was demonstrated, and a specific capacity above 200 mAh g−1 was retained with a current density of 257 mA g−1.

The effect of Cu (I) and Cu (II) ions' low concentrations on growth, biohydrogen production and the FoF1-ATPase activity of Rhodobacter sphaeroides

Various metal ions play a key role in growth and biohydrogen (H2) production by phototrophic bacteria through incorporation into or stimulation of the responsible enzymes and/or related metabolic pathways. This study shows, that Cu (I) ions, at low concentration (<5 μM), suppressed the growth of Rhodobacter sphaeroides strain MDC6521, isolated from mineral springs in Armenia, but enhanced the H2 yield by this bacterium. In contrast, Cu (II) ions with the same concentrations inhibited H2 yield. These ions also affected the medium redox potential during R. sphaeroides growth. N,N′-dicyclohexylcarbodiimide-sensitive ATPase activity of R. sphaeroides membrane vesicles was increased in the presence of both ions. Cu ions at low concentrations are suggested to affect biohydrogen production pathways or responsible enzymes in R. sphaeroides, proton FoF1-ATPase of which could be a target for these ions.

Generation of electric potential difference across the electrodes of the microbial fuel cell in the anaerobic oxidation of substrates by microbial associations

Several microbial associations were obtained from natural and anthropogenic sources. All of the associations grow well on glucose and significantly worse on acetate. We observed 80–95% glucose consumption during 3–5 days of growth. The oxidation of substrates by the cultures generates an electric potential difference between anode and cathode electrodes of a microbial fuel cell (MFC). The value of the potential difference depends on the nature of the association and the substrate and reaches 400–500 mV. The potential difference generation accompanied by a shift to the negative region of the medium redox potential (Eh) to — (400–500) mV. This indicates H2 evolution by the association cultures during oxidation of carbohydrates. Artificial redox mediators, such as tetramethyl-p-phenylenediamine, phenazine methosulfate, and benzyl viologen, were able to increase up to 15% the difference in electrical potential across the electrodes of the MFC. It is assumed that an increase in the potential difference across the electrodes induced by the redox mediators is due to their direct involvement in the transfer of electrons from the bacteria in the incubation medium to the MFC anode electrode. The direct measurement of current and potential difference on the electrodes in a short-circuit mode shows that the internal resistance of the MFC is equal to 1 kΩ and the power reaches 5 μW. Undoubtedly, this testifies to the low efficiency developed by the MFE.

Labile iron in cells and body fluids: physiology, pathology, and pharmacology

In living systems iron appears predominantly associated with proteins, but can also be detected in forms referred as labile iron, which denotes the combined redox properties of iron and its amenability to exchange between ligands, including chelators. The labile cell iron (LCI) composition varies with metal concentration and substances with chelating groups but also with pH and the medium redox potential. Although physiologically in the lower μM range, LCI plays a key role in cell iron economy as cross-roads of metabolic pathways. LCI levels are continually regulated by an iron-responsive machinery that balances iron uptake versus deposition into ferritin. However, LCI rises aberrantly in some cell types due to faulty cell utilization pathways or infiltration by pathological iron forms that are found in hemosiderotic plasma. As LCI attains pathological levels, it can catalyze reactive O species (ROS) formation that, at particular threshold, can surpass cellular anti-oxidant capacities and seriously damage its constituents. While in normal plasma and interstitial fluids, virtually all iron is securely carried by circulating transferrin (Tf; that renders iron essentially non-labile), in systemic iron overload (IO), the total plasma iron binding capacity is often surpassed by a massive iron influx from hyperabsorptive gut or from erythrocyte overburdened spleen and/or liver. As plasma Tf approaches iron saturation, labile plasma iron (LPI) emerges in forms that can infiltrate cells by unregulated routes and raise LCI to toxic levels. Despite the limited knowledge available on LPI speciation in different types and degrees of IO, LPI measurements can be and are in fact used for identifying systemic IO and for initiating/adjusting chelation regimens to attain full-day LPI protection. A recent application of labile iron assay is the detection of labile components in intravenous iron formulations per se as well as in plasma (LPI) following parenteral iron administration.

Improved methods for investigating the external redox potential in hybridoma cell culture

Because of the interest in understanding and optimizing secretion of proteins from mammalian cells, reliable and more reproducible methods are needed to monitor the external redox potential of animal cells in suspension culture. An improved off-line method was established that greatly reduces the typically long response time of redox electrodes in cell culture media and improves the standardization of redox probes. In addition, the dependence of medium redox potential on dissolved oxygen concentrations and pH was investigated using cell-free medium. Off-line as well as on-line redox potential measurements were then applied to spinner or bioreactor cultures of murine hybridoma cells. Serum containing or protein-free medium were used. The time dependence of the experimentally determined external redox potential was found to be affected not only by oxygen, pH, and medium composition. but to a significant extent by the rate of generation of reductants by hybridoma cells. The observed specific rate of medium reduction by generation of reductants (ΔmV h(-1) viable cell(-1)) decreased during exponential growth while cell number increased from 2×10(5) viable cells ml(-1) to 3.5×10(6) viable cells ml(-1). This rate, however, was essentially constant at -7.3 mV h(-1)±3.7 mV h(-1) per 10(10) viable cells during growth under conditions of constant dissolved oxygen tension and constant pH. Using these observations, the quantity of reductants synthesized and secreted into the medium by viable hybridoma cells was estimated to be approximately 1.3 mole h(-1) per 10(10) viable hybridoma cells. The time course of specific monoclonal antibody secretion rate did not correlate with changes in the external oxidation/reduction potential in either serum containing or protein-free medium.

Effect of redox potential on methanogenesis by Methanosarcina barkeri

Concentrations of 0.5% O2 immediately inhibited CH4 production from methanol by Methanosarcina barkeri. Simultaneously, the redox potential of the medium increased to about +100 mV. However, the rates of CH4 production were not significantly affected, when the redox potential of an anoxic medium was adjusted to values between -420 mV and +100 mV by addition of titanium (III) citrate, sodium dithionite, flavin adenine dinucleotide, or sodium ascorbate. When the redox potential was adjusted to values between -80 mV and +550 mV by means of mixtures of ferrocyanide and ferricyanide, CH4 production was not inhibited until a redox potential of about +420 mV was reached. M. barkeri was able to reduce 0.5 mM ferricyanide solution at +430 mV within 0.005%.

Enhanced cell density culture of Thiobacillus ferrooxidans in membrane-type bioreactor with electrolytic reduction unit for ferric ion.

Enhanced cell density culture of Thiobacillus ferrooxidans was achieved by using a membrane-type bioreactor with cell filtration and iron recycling units. Using an electrolytic bath with an anion exchange membrane, microbially produced Fe3+ could be reduced to Fe2+ without loss of main nutrients in the medium. It was confirmed that T. ferrooxidans exhibited active growth in the electrochemically regenerated medium. In the repeated-batch culture with cell filtration and feeding of the regenerated medium, the cell concentration obtained was at least 4–11 times higher than that in a conventional batch culture. In this culture system, the measurement of medium redox potential made it possible to estimate the concentrations of cells and iron, and to determine the time for culture filtration and medium-feeding operations.

Regulation of intracellular H+ balance in Zymomonas mobilis 113 during the shift from anaerobic to aerobic conditions

The energetics, enzyme activities and end-product synthesis of Zymomonas mobilis 113 in continuous culture were studied after the shift from an anaerobic to an aerobic environment. Aeration diminished ethanol yield and lactic acid concentration, but increased glucose consumption rate and production of acetic acid. After the shift to aerobic conditions reduced nicotinamide adenine dinucleotide (phosphate) [NAD(P)H]-oxidase activity was stimulated. Washed cell suspensions consumed oxygen with glucose, lactate and ethanol as substrates. The aerobic Z. mobilis 113 regulated their intracellular redox balance by production and reoxidation of the end products, coupled with the formation of NAD(P)H. An increase in transmembrane pH gradient (ΔpH) and a decrease in intracellular ATP concentration were observed after the shift to aerobic conditions. At low medium redox potential (Eh) values the H+ balance was regulated in an energy-independent way via end-product excretion. Under aerobic conditions this was supplemented by ATP-dependent H+ excretion by the membrane H+-ATPase.

Self-limitation of the oxidative burst of rat polymorphonuclear leukocytes.

The oxidative response of rat polymorphonuclear leukocytes stimulated by phorbol myristate acetate and N-formyl-methionyl-leucyl-phenylalanine was studied. Ferricytochrome reduction and peroxidase-catalyzed decrease of scopoletin fluorescence were used to monitor O-2 and H2O2 release in the extracellular medium. Oxygen consumption was also measured in some experiments. Decrease of chlortetracyclin fluorescence after stimulation of dye-loaded cells was used to study an early step of cell stimulation. Finally, a possible relationship between cell responses and the medium redox potential was explored. Three major conclusions were obtained: Ferricytochrome reduction is dependent on the total cytochrome concentration, and a simple mathematical model allows a tentative estimate of total superoxide anion production by stimulated cells. Increasing cell concentration results in a decrease of individual cell response, and this may be accounted for by a direct inhibition of cell-released hydrogen peroxide on the reactivity of leukocytes. Further, H2O2 may be shown to inhibit an early step of cell response. The solution redox potential does not influence cell reactivity, since it may be dramatically decreased without inhibiting cell response.

Effect of titanium (III) citrate as reducing agent on growth of rumen bacteria.

We compared the growth of 10 strains of rumen bacteria in an anaerobic medium reduced with cysteine hydrochloride, dithiothreitol, or titanium (III) citrate. The redox potential of medium reduced with cysteine hydrochloride was -167.8 mV; with dithiothreitol it was -175.8 mV; and with titanium(III) citrate it was -302.4 mV at a concentration of 5 X 10(-4) M titanium and -403.9 mV at 2 X 10(-3) M titanium. Maximum growth of the strains was generally lower with dithiothreitol or titanium(III) citrate than with cysteine hydrochloride, although growth was greater than in medium lacking an added reducing agent. Strains for which cysteine was required or markedly stimulatory grew only poorly with titanium(III) citrate. No strain grew in medium with sodium citrate as the energy source. Titanium(III) citrate could be used to reduce anaerobic media for some rumen bacteria if the exclusion of a sulfur-containing reducing agent is required.

The effect of medium redox potential on the folate-limited growth of Lactobacillus casei var. rhamnosus.

The medium redox potential (Eh) influenced the folate-limited growth of Lactobacillus casei; the growth response was maximal at an Eh of +120 mV (pH 6-35). At raised Eh serum folate would support less growth than pteroylglutamic acid, and the response to N5-methyl tetrahydrofolic acid was intermediate between them. Pteroylglutamic acid was not destroyed during 24 h incubation at 37 degrees C in medium with Eh values between +40 and +440 mV. Destruction of N5-methyl tetrahydrofolic acid occurred within 24 h when the medium Eh was greater than +125 mV. Folate was taken up rapidly by L. casei with an Eh optimum at +270 mV.