Oxygen: From Toxic Waste to Optimal (Toxic) Fuel of Life

Some 2.5 billion years ago, the great oxygenation event (GOE) led to a 105‐fold rise in atmospheric oxygen [O2], killing most species on Earth. In spite of the tendency to produce toxic reactive oxygen species (ROS), the highly exergonic reduction of O2 made it the ideal biological electron acceptor. During aerobic metabolism, O2 is reduced to water liberating energy, which is coupled to adenosine triphosphate (ATP) synthesis. Today, all organisms either aerobic or not need to deal with O2 toxicity. O2‐permeant organisms need to seek adequate [O2], for example, aquatic crustaceans bury themselves in the sea bottom where O2 is scarce. Also, the intestinal lumen and cytoplasm of eukaryotes is a microaerobic environment where many facultative bacteria or intracellular symbionts hide from oxygen. Organisms such as plants, fish, reptiles and mammals developed O2‐impermeable epithelia, plus specialized external respiratory systems in combination with O2‐binding proteins such as hemoglobin or leg‐hemoglobin control [O2] in tissues. Inside the cell, ROS production is prevented by rapid O2 consumption during the oxidative phosphorylation (OxPhos) of ATP. When ATP is in excess, OxPhos becomes uncoupled in an effort to continue eliminating O2. Branched respiratory chains, unspecific pores and uncoupling proteins (UCPs) uncouple OxPhos. One last line of resistance against ROS is deactivation by enzymes such as super oxide dismutase and catalase. Aerobic organisms profit from the high energy released by the reduction of O2, while at the same time they need to avoid the toxicity of ROS

DISEÑO DE UN BUS DE CD CON FUENTES ASIMÉTRICAS APLICABLE A ENERGÍAS RENOVABLES (DESIGN OF A DC BUS WITH ASYMMETRIC SOURCES APPLICABLE TO RENEWABLE ENERGIES)

ResumenLos sistemas convencionales de energía enfrentan problemas que han conducido a la generación de manera local utilizando fuentes alternativas. En la búsqueda por mejorar el desempeño de las energías limpias, se han desarrollado una gran variedad de convertidores electrónicos. En este trabajo se presenta la propuesta de un bus de corriente directa, para demostrar que se puede manejar la energía de dos fuentes renovables asimétricas. Se presentan los conceptos teóricos utilizados, así como los cálculos de los parámetros de diseño. En función de los resultados de simulación en Pspice de la microred propuesta, así como la implementación física de la misma se puede comprobar el buen desempeño del bus propuesto. Palabras Claves: Energía, renovable, microred, bus, CD. AbstractConventional energy systems face problems that have led to the local generation using alternative sources. In the search to improve the performance of clean energies, a wide variety of electronic converters have been developed. This paper presents the proposal of a direct current bus, to demonstrate that energy from two asymmetric renewable sources can be managed. The theoretical concepts used are presented, as well as the calculations of the design parameters. Depending on the simulation results in Pspice of the proposed micro-network, as well as its physical implementation, the good performance of the proposed bus can be verified.    Keywords: Energy, renowable, microgrids, bus, DC.

High Osmolarity Environments Activate the Mitochondrial Alternative Oxidase in Debaryomyces Hansenii.

The oleaginous yeast Debaryomyces hansenii is a good model to understand molecular mechanisms involved in halotolerance because of its impressive ability to survive under a wide range of salt concentrations. Several cellular adaptations are implicated in this response, including the presence of a cyanide-insensitive ubiquinol oxidase (Aox). This protein, which is present in several taxonomical orders, has been related to different stress responses. However, little is known about its role in mitochondria during transitions from low to high saline environments. In this report, we analyze the effects of Aox in shifts from low to high salt concentrations in the culture media. At early stages of a salt insult, we observed that this protein prevents the overflow of electrons on the mitochondrial respiratory chain, thus, decreasing the production of reactive oxygen species. Interestingly, in the presence of high osmolite concentrations, Aox activity is able to sustain a stable membrane potential when coupled to complex I, despite a compromised cytochrome pathway. Taken together, our results suggest that under high osmolarity conditions Aox plays a critical role regulating mitochondrial physiology

High osmolarity promotes higher resistance to oxidative stress.

<p>(A) Hydrogen peroxide production rates in isolated mitochondria. Isolated mitochondria (0.5 mg/mL) from cells in each experimental condition were assayed for hydrogen peroxide production using 1 mM NADH as a respiratory substrate. White bars, basal hydrogen peroxide production. Light gray bars, hydrogen peroxide production in the presence of 100 μM SHAM. Dark gray, hydrogen peroxide production in the presence of 1 μM antimycin A. (B) Cells grown YPD media (white bars) or YPD+SHAM (3 mM, gray bars) were treated with 10 mM hydrogen peroxide for 10 minutes, samples were plated on YPD and incubated at 29°C for 2 days. Colonies were manually counted. *<i>p</i> < 0.05 respect to basal oxidant production (white bars, panel A), #<i>p</i> < 0.05 respect to oxidant production in the presence of SHAM (Light gray bars, panel A) For panel B, *<i>p</i> < 0.05 respect to control cells with SHAM. # <i>p</i> < 0.05 respect to control without SHAM.</p

Alternative oxidase activity is necessary for growth in high osmolarity media.

<p>(A) Cells were grown in YPD media with and without NaCl, KCl or sorbitol (white bars). Some plates were supplemented with 3 mM SHAM (gray bars) to determine the effect of Aox on hyperosmotic media. Samples were spread on YPD plates at 28°C and colonies were counted after 2 days. (B) Representative plates of serially diluted samples to show the effect of 3 mM SHAM on cell grown in the presence of the indicated osmolites. Ctrl, YPD media, Na⁺, YPD plus 0.6 M NaCl, S, YPD, YPD media plus 1.2 M sorbitol, K⁺, YPD media plus 0.6 M KCl. (C-D) Compatible solute production in the cells grown in the presence of the indicated osmolites. Cells grown in the indicated media were lysed and extracts assayed for trehalose (C) and glycerol (D) content. * <i>p</i> < 0.05 respect to control cells.</p

Simplified representation of the respiratory chain of <i>Debaryomyces hansenii</i>.

<p><i>Debaryomyces hansenii</i> has a proton-pumping complex I, a canonical proton-pumping cytochrome pathway (complex III-IV) and a cyanide-resistant terminal oxidase (Aox). For simplicity, the alternative NADH dehydrogenase and glycerol-3-phosphate dehydrogenase described in [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0169621#pone.0169621.ref009" target="_blank">9</a>] are not depicted. Electrons flow from complex I to ubiquinone and at this point the respiratory chain is branched and electrons flow to complex III and the Aox. Thus, two electron pathways are able to sustain a protonmotive force: Complex I-Aox and Complex I-III-IV.</p

Increases in osmolarity in glucose media promote cyanide-resistance respiration.

<p>(A) Cyanide-resistant respiration in cells grown in YPD. Cells (1 mg.mL^-1) were incubated in respiration buffer. To induced Aox-dependent respiration, 25 mM glucose and 0.5 mM potassium cyanide (KCN) were included in the incubation media. (B-D) Densitometry analysis of the expression of the Aox (Panel B) and cytochrome <i>c</i> oxidase subunit III (CoxIII, Panel C) in glucose media in the presence of 0.6 M NaCl, 1.2 M sorbitol or 0.6 M KCl. (D) Representative blots of Aox and CoxIII expression.</p

Aox sustains a membrane potential (ΔΨ) when coupled to complex I.

<p>(A) Representative plot of mitochondrial membrane potential measurements in intact cells grown in glucose media Where indicated, 25 mM glucose, 0.5 μM antimycin A (AA), 3 mM SHAM and 10 μM CCCP (U) were added. Cells were incubated in regular respiration media at a final concentration of 1 mg.mL^-1 (B) Aox-dependent ΔΨ measured as the difference between maximum fluorescence (glucose) and the fluorescence after Aox inhibition (SHAM). (C-E) Representative ΔΨ plots of isolated mitochondria from cells grown in YPD. (C) Complex I-dependent ΔΨ (10 mM pyruvate/malate/citrate each). Traces: Black, control without inhibitors. Red, Aox-sustained ΔΨ, in the presence of 100 μM cyanide (addition where indicated). Green/Blue, contribution of the cytochromes to the ΔΨ after the addition of 100μM salicylhydroxamic acid (SHAM, green) and 1 μM propyl gallate (PG, blue). (D) ΔΨ- dependent on Aox. Traces: Black, control without inhibitors. Blue/Red after addition of 100μM SHAM (blue) and 1 mM PG (Green) respectively. (F) Succinate/rotenone (10 mM/ 1 μM) dependent ΔΨ. Traces: Blue, complete collapse of ΔΨ after 100 μM cyanide addition. Black/Red, inhibition of Aox by SHAM (black) or PG (red) did not exert any effect on the ΔΨ, complete collapse of ΔΨ under these conditions was obtained after addition of 100 μM cyanide. At the end of all plots, 1 μM CCCP (U) was added to completely collapse the ΔΨ. <i>* p</i> < 0.05 respect to control cells.</p