Oxygen

About: Oxygen is a research topic. Over the lifetime, 48149 publications have been published within this topic receiving 1113788 citations. The topic is also known as: O & Oxygen.

Pathways of peroxynitrite oxidation of thiol groups

Abstract: Peroxynitrite mediates the oxidation of the thiol group of both cysteine and glutathione. This process is associated with oxygen consumption. At acidic pH and a cysteine/peroxynitrite molar ratio of < or = 1.2, there was a single fast phase of oxygen consumption, which increased with increasing concentrations of both cysteine and oxygen. At higher molar ratios the profile of oxygen consumption became biphasic, with a fast phase (phase I) that decreased with increasing cysteine concentration, followed by a slow phase (phase II) whose rate of oxygen consumption increased with increasing cysteine concentration. Oxygen consumption in phase I was inhibited by desferrioxamine and 5,5-dimethyl-1-pyrroline N-oxide, but not by mannitol; superoxide dismutase also inhibited oxygen consumption in phase I, while catalase added during phase II decreased the rate of oxygen consumption. For both cysteine and glutathione, oxygen consumption in phase I was maximal at neutral to acidic pH: in contrast, total thiol oxidation was maximal at alkaline pH. EPR spin-trapping studies using N-tert-butyl-alpha-phenylnitrone indicated that the yield of thiyl radical adducts had a pH profile comparable with that found for oxygen consumption. The apparent second-order rate constants for the reactions of peroxynitrite with cysteine and glutathione were 1290 +/- 30 M-1.S-1 and 281 +/- 6 M-1.S-1 respectively at pH 5.75 and 37 degrees C. These results are consistent with two different pathways participating in the reaction of peroxynitrite with low-molecular-mass thiols: (a) the reaction of the peroxynitrite anion with the protonated thiol group, in a second-order process likely to involve a two-electron oxidation, and (b) the reaction of peroxynitrous acid, or a secondary species derived from it, with the thiolate in a one-electron transfer process that yields thiyl radicals capable of initiating an oxygen-dependent radical chain reaction.

High phosphorylation efficiency and depression of uncoupled respiration in mitochondria under hypoxia

Abstract: Mitochondria are confronted with low oxygen levels in the microenvironment within tissues; yet, isolated mitochondria are routinely studied under air-saturated conditions that are effectively hyperoxic, increase oxidative stress, and may impair mitochondrial function. Under hypoxia, on the other hand, respiration and ATP supply are restricted. Under these conditions of oxygen limitation, any compromise in the coupling of oxidative phosphorylation to oxygen consumption could accentuate ATP depletion, leading to metabolic failure. To address this issue, we have developed the approach of oxygen-injection microcalorimetry and ADP-injection respirometry for evaluating mitochondrial function at limiting oxygen supply. Whereas phosphorylation efficiency drops during ADP limitation at high oxygen levels, we show here that oxidative phosphorylation is more efficient at low oxygen than at air saturation, as indicated by higher ratios of ADP flux to total oxygen flux at identical submaximal rates of ATP synthesis. At low oxygen, the proton leak and uncoupled respiration are depressed, thus reducing maintenance energy expenditure. This indicates the importance of low intracellular oxygen levels in avoiding oxidative stress and protecting bioenergetic efficiency.

Photoinhibition of Photosynthesis in Vivo Results in Singlet Oxygen Production Detection via Nitroxide-Induced Fluorescence Quenching in Broad Bean Leaves†

Abstract: In plants experiencing environmental stress, the formation of reactive oxygen is often presumed. In this study, singlet oxygen was detected in broad bean (Vicia faba) leaves that were photoinhibite...

Ether-Based Electrolytes for the Lithium/Oxygen Organic Electrolyte Battery

Abstract: The practical operation of a lithium/oxygen organic electrolyte battery depends on a significant amount of dissolved oxygen transporting through the organic electrolyte permeating the carbon black cathode before its reduction occurs. The rate of oxygen transport directly influences rate capability and discharge capacity. The organic electrolyte can be tailored to maximize the transport of oxygen while still retaining the ability to form a stable solid electrolyte interface with the lithium anode, chemical stability towards the discharge products Li 2 O 2 and Li 2 O, and oxidative stability to over 3 V. We investigated an ether-based electrolyte containing four different electrolyte salts to determine how electrolyte properties such as oxygen solubility, dynamic viscosity, and conductivity change with each electrolyte salt, and how this directly affects rate capability and discharge capacity. The results indicate that discharge capacity at 0.5 mA/cm 2 is determined by dynamic viscosity alone for these electrolytes, while discharge capacity at 0.2 and 0.05 mA/cm 2 shows no correlation with either oxygen solubility, dynamic viscosity, or conductivity. Our results demonstrate that a substantial improvement in rate capability can be achieved by optimizing electrolyte viscosity.