Stimulation of onion root elongation by ascorbate and ascorbate free radical inAllium cepa L.

Summary We report that ascorbate free radical stimulates onion root growth at 15 °C and 25 °C. The fully reduced form, ascorbate, also stimulates root elongation if culture conditions allow its oxidation. When ascorbate oxidation was inhibited, no stimulation of root growth was found. The effect of the fully oxidized form, dehydroascorbate, was inhibitory. We show also that ascorbate free radical generated by ascorbate oxidation, is reduced back probably by a transplasmalemma reductase. These results are discussed on the basis of an activation of a transplasma membrane redox system likely involved in processes related to cell growth.Abbreviations AFR ascorbate free radical - ASC ascorbate - DHA dehydroascorbate     

Effect of bicarbonate and oxaloacetate on malate oxidation by spinach leaf mitochondria

Mitochondria isolated from spinach leaves oxidized malate by both a NAD⁺-linked malic enzyme and malate dehydrogenase. In the presence of sodium arsenite the accumulation of oxaloacetate and pyruvate during malate oxidation was strongly dependent on the malate concentration, the pH in the reaction medium and the metabolic state condition.Bicarbonate, especially at alkaline pH, inhibited the decarboxylation of malate by the NAD⁺-linked malic enzyme in vitro and in vivo. Analysis of the reaction products showed that with 15 mM bicarbonate, spinach leaf mitochondria excreted almost exclusively oxaloacetate.The inhibition by oxaloacetate of malate oxidation by spinach leaf mitochondria was strongly dependent on malate concentration, the pH in the reaction medium and on the metabolic state condition.The data were interpreted as indicating that: (a) the concentration of oxaloacetate on both sides of the inner mitochondrial membrane governed the efflux and influx of oxaloacetate; (b) the NAD⁺/NADH ratio played an important role in regulating malate oxidation in plant mitochondria; (c) both enzymes (malate dehydrogenase and NAD⁺-linked malic enzyme) were competing at the level of the pyridine nucleotide pool, and (d) the NAD⁺-linked malic enzyme provided NADH for the reversal of the reaction catalyzed by the malate dehydrogenase.     

Optimization of pulp density and particle size in the biooxidation of a pyritic gold concentrate by <Emphasis Type="Italic">Sulfolobus metallicus</Emphasis>

Although increasing pulp densities and decreasing particle sizes have positive effects in the volumetric rate of biooxidation of refractory gold concentrates, a variety of phenomena such as mechanical damage, metabolic stress and inhibition can limit this effect. The objective of this work was to determine pulp density and particle size values that maximize the volumetric solubilization rate of iron from a pyritic gold concentrate. The leaching was carried on in agitated flasks with the thermophilic archaeon Sulfolobus metallicus. The concentrate contained 66.7% pyrite, and the constant operation conditions were 220 rev/min, 68 °C and initial pH of 2.0. Pulp densities were 2.5, 5, 10 and 15% w/v and the size fractions were 150–106, 106–75, 75–38 and <38 m. Total solubilized iron concentrations were in the range of 8–25 g/l. In the 2.5 and 5% pulp density runs, iron extractions were in the range of 80–100%. A complete experimental design of 16 runs allowed the building of response surfaces from which the optimal conditions that maximize the rate of iron solubilization were determined. These conditions are 7.8% pulp density and particle size of 35 m.     

Sirt3 modulates fatty acid oxidation and attenuates cisplatin‐induced AKI in mice

Fatty acid oxidation (FAO) dysfunction is one of the important mechanisms of renal fibrosis. Sirtuin 3 (Sirt3) has been confirmed to alleviate acute kidney injury (AKI) by improving mitochondrial function and participate in the regulation of FAO in other disease models. However, it is not clear whether Sirt3 is involved in regulating FAO to improve the prognosis of AKI induced by cisplatin. Here, using a murine model of cisplatin‐induced AKI, we revealed that there were significantly FAO dysfunction and extensive lipid deposition in the mice with AKI. Metabolomics analysis suggested reprogrammed energy metabolism and decreased ATP production. In addition, fatty acid deposition can increase reactive oxygen species (ROS) production and induce apoptosis. Our data suggested that Sirt3 deletion aggravated FAO dysfunction, resulting in increased apoptosis of kidney tissues and aggravated renal injury. The activation of Sirt3 by honokiol could improve FAO and renal function and reduced fatty acid deposition in wide‐type mice, but not Sirt3‐defective mice. We concluded that Sirt3 may regulate FAO by deacetylating liver kinase B1 and activating AMP‐activated protein kinase. Also, the activation of Sirt3 by honokiol increased ATP production as well as reduced ROS and lipid peroxidation through improving mitochondrial function. Collectively, these results provide new evidence that Sirt3 is protective against AKI. Enhancing Sirt3 to improve FAO may be a potential strategy to prevent kidney injury in the future.     

Structural and chemical trapping of flavin‐oxide intermediates reveals substrate‐directed reaction multiplicity

Though reactive flavin‐N5/C4α‐oxide intermediates can be spectroscopically profiled for some flavin‐assisted enzymatic reactions, their exact chemical configurations are hardly visualized. Structural systems biology and stable isotopic labelling techniques were exploited to correct this stereotypical view. Three transition‐like complexes, the α‐ketoacid…N5‐FMN_ox complex ( I ), the FMN_ox‐N5‐aloxyl‐C′α^?‐C4α⁺ zwitterion ( II ), and the FMN‐N5‐ethenol‐N5‐C4α‐epoxide ( III ), were determined from mandelate oxidase (Hmo) or its mutant Y128F (monooxygenase) crystals soaked with monofluoropyruvate (a product mimic), establishing that N5 of FMN_ox an alternative reaction center can polarize to an ylide‐like mesomer in the active site. In contrast, four distinct flavin‐C4α‐oxide adducts ( IV – VII ) from Y128F crystals soaked with selected substrates materialize C4α of FMN an intrinsic reaction center, witnessing oxidation, Baeyer–Villiger/peroxide‐assisted decarboxylation, and epoxidation reactions. In conjunction with stopped‐flow kinetics, the multifaceted flavin‐dependent reaction continuum is physically dissected at molecular level for the first time.     

Circular Dichroism and NMR Studies of Metabolically Stableα-Methylpolyamines: Spectral Comparison with Naturally Occurring Polyamines

Three synthetic polyamine analogs, α-methylspermine, and α,α′-dimethylspermine, were compared with their naturally occurring counterparts, spermidine and spermine, by two different spectral techniques. The interaction of polyamines with oligodeoxynucleotides was measured by circular dichroism in order to monitor the polyamine-induced conversion of right-handed B-DNA to the left-handed Z-form. The methylated analogs were shown to be equally effective as the natural polyamines in inducing the B → Z transition. The pH dependence of the chemical shift of all carbon atoms in each of the five polyamines was measured by ¹³C-NMR spectroscopy. With the exception of expected changes in chemical shift due to the presence of the α-methyl substituents, the chemical shifts and pH dependence of all carbon atoms in the three α-methyl polyamines were similar to the corresponding naturally occurring polyamines. The combined data indicate that α-methyl polyamines have physical properties that are very similar to their natural counterparts. The two metabolically stable polyamine analogs, α-methylspermidine and α,α′-dimethylspermine, are therefore useful surrogates for spermidine and spermine in the study of numerous polyamine-mediated effects in mammalian cell cultures and can be used in such studies without the requirement for coadministration of amine oxidase inhibitors.     

Metabolic Flexibility and Substrate Preference by the Fe(II)-Oxidizing Purple Non-Sulphur Bacterium Rhodopseudomonas palustris Strain TIE-1

It is unknown to which extent phototrophic Fe(II) oxidation takes place in the simultaneous presence of organic electron donors (e.g., acetate/lactate). Therefore, the photoferrotrophic strain Rhodopseudomonas palustris TIE-1 was inoculated with various combinations of Fe(II), acetate and lactate to understand metabolic substrate preference. When acetate was provided together with Fe(II), TIE-1 consumed acetate first before Fe(II). When provided lactate plus Fe(II), TIE-1 consumed both substrates in parallel. When all three substrates were provided in one culture, TIE-1 used all substrates simultaneously. Our study suggests that the availability of alternative electron donors in addition to ferrous iron limits phototrophic iron oxidation.     

Copper generated reactive oxygen leads to formation of lysine-DNA adducts

This work describes the addition of a lysine derivative to guanine base in a nucleoside, an oligonucleotide, and to a large DNA that occurs via oxidation by copper generated reactive oxygen species. Nucleophiles present during oxidation leads to the formation of adducts. In this work, 2′-deoxyguanosine is oxidized by copper generated reactive oxygen species in the presence of a lysine derivative, Nα-acetyl-lysine methyl ester. Under these conditions the guanidinohydantoin-lysine adduct is observed in a relative yield of 27% when compared to other guanine oxidation products. MS² strongly supports that lysine is added to the 5-position during the formation of guanidinohydantoin-lysine. A fourteen-nucleotide DNA duplex was oxidized under similar conditions. Digestion showed formation of the same guanidinohydantoin-lysine nucleoside. The reaction was then examined on a 392-nucleotide DNA substrate. Oxidation in the presence of the lysine ester showed adduct formation as stops in a primer extension assay. Adducts predominately formed at a 5′-GGG at position 415. Six of the seven sites that showed reaction greater than 3-fold above background were guanine sites. We conclude from this study that copper can catalyze the formation of DNA-protein adducts and may form in cells with elevated copper and oxidative stress.     

Photoinduced oxidation of a tris(2,2'‐bipyridyl)ruthenium(II)–peroxodisulfate chemiluminescence system for the analysis of mebeverine HCl pharmaceutical formulations and biological fluids using a two‐chip device

A new method for the analysis of mebeverine hydrochloride (MEB) has been developed using a two‐chip device. The method is highly selective, sensitive, rapid and consumes minute amount of reagents. The developed method is free of interference from the degradation products of MEB and from common ingredients present in pharmaceutical formulations. The limit of detection was 0.043 µg/mL, and the limit of quantification was 0.138 µg/mL. The short analysis time per sample (20 s) allowed a large number of analyses to be performed within a very short time. Various samples were analyzed, including two different pharmaceutical formulations and a uniformity of content analysis for 20 tablets from a known batch and two biological samples at different concentrations. In addition, the method was compared with a validated high‐performance liquid chromatography (HPLC) method and the results clearly indicated the suitability of the developed method for routine analyses. A new mechanism for the tris(2,2'‐bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺)‐peroxodisulfate (S₂O₈^2?) chemiluminescence (CL) system has also been proposed. The mechanism is based on photoinduced oxidation of Ru(bpy)₃²⁺ to Ru(bpy)₃³⁺ via the formation of Ru(bpy)₃²⁺* upon irradiation with visible light. S₂O₈^2? then oxidizes Ru(bpy)₃²⁺* to Ru(bpy)₃³⁺ and the analyte subsequently reduces the resultant Ru(bpy)₃³⁺ to Ru(bpy)₃²⁺*, which then produces the CL signal. Copyright © 2013 John Wiley & Sons, Ltd.     

Responses from freshwater sediment during electricity generation using microbial fuel cells

In a two-electrode system, freshwater sediment was used as a fuel to examine the relationship between current generation and organic matter consumption with different types of electrode. Sediment microbial fuel cells using porous electrodes showed a superior performance in terms of generating current when compared with the use of non-porous electrodes. The maximum current densities with thicker and thin porous electrodes were 45.4 and 37.6 mA m⁻², respectively, whereas the value with non-porous electrodes was 13.9 mA m⁻². The amount of organic matter removed correlated with the current produced. The redox potential in the anode area under closed-circuit conditions was +246.3 ± 67.7 mV, while that under open-circuit conditions only reached −143.0 ± 7.18 mV. This suggests that an application of this system in organic-rich sediment could provide environmental benefits such as decreasing organic matter and prohibiting methane emission in conjunction with electricity production via an anaerobic oxidation process.