The relative effectiveness of .OH,H2O2,O2−, and reducing free radicals in causing damage to biomembranes: A study of radiation damage to erythrocyte ghosts using selective free radical scavengers

The relative effectiveness of oxidizing (^.OH, H₂O₂), ambivalent (O₂^?) and reducing free radicals (e^? and CO₂^?) in causing damage to membranes and membrane-bound glyceraldehyde-3-phosphate dehydrogenase of resealed erythrocyte ghosts has been determined. The rates of damage to membranebound glyceraldehyde-3-phosphate dehydrogenase ($\text{R}$(enz)) were measured and the rates of damage to membranes ($\text{R}$(mb)) were assessed by measuring changes in permeability of the resealed ghosts to the relatively low molecular weight substrates of glyceraldehyde-3-phosphate dehydrogenase. Each radical was selectively isolated from the mixture produced during gamma-irradiation, using appropriate mixtures of scavengers such as catalase, superoxide dismutase and formate. ^.OH, O₂^? and H₂ O₂ were approximately equally effective in inactivating membrane-bound glyceraldehyde-3-phosphate dehydrogenase, while e^? and CO₂^? were the least effective. $\text{R}$(enz) values of O₂^? and H₂O₂ were 10-times and of ^.OH 15-times that of e^?. $\text{R}$(mb) values were quite similar for e^? and H₂O₂ (about twice that of O₂^?), while that of ^.OH was 3-times that of O₂^?. Hence, with respect to $\text{R}$(mb): ${}^{\mathrm{.}}\text{OH}\text{>}\text{e}{}^{\mathrm{?}}\text{=}\text{H}{}_2\text{O}{}_2\text{>}\text{O}{}_2{}^{\mathrm{?}}$ , and with respect to $\text{R}$(enz): ${}^{\mathrm{.}}\text{OH}\text{>}\text{O}{}_2{}^{\mathrm{?}}\text{=}\text{H}{}_2\text{O}{}_2\text{>}\text{e}{}^{\mathrm{?}}$. The difference between the effectiveness of the most damaging and the least damaging free radicals was more than 10-fold greater in damage to the enzyme than to the membranes. Comparison between H₂O₂ added as a chemical reagent and H₂O₂ formed by irradiation showed that membranes and membrane-bound glyceraldehyde-3-phosphate dehydrogenase were relatively inert to reagent H₂O₂ but markedly susceptible to the latter.     

Microbial processes of the carbon and sulfur cycles in the Chukchi Sea

The research performed in August 2004 within the framework of the Russian-American Long-term Census of the Arctic (RUSALCA) resulted in the first data concerning the rates of the key microbial processes in the water column and bottom sediments of the Bering strait and the Chukchi Sea. The total bacterial counts in the water column varied from 30 × 10³ cells ml^?1 in the northern and eastern parts to 245 × 10³ cells ml^?1 in the southern part. The methane content in the water column of the Chukchi sea varied from 8 nmol CH₄l^?1 in the eastern part of the sea to 31 nmol CH₄l^?1 in the northern part of the Herald Canyon. Microbial activity occurred in the upper 0–3 cm of the bottom sediments; the methane formation rate varied from 0.25 to 16 nmol CH₄dm^?3 day^?1. The rates of methane oxidation varied from 1.61 to 14.7 nmol CH₄dm^?3 day^?1. The rates of sulfate reduction varied from 1.35 to 16.2 μmol SO ₄ ^2? dm^?1 day^?1. The rate of methane formation in the sediments increased with depth, while sulfate reduction rates decreased (less than 1 μmol SO ₄ ^2? dm^?3 day^?1). These high concentrations of biogenic elements and high rates of microbial processes in the upper sediment layers suggest a specific type of trophic chain in the Chukchi Sea. The approximate calculated balance of methane emission from the water column into the atmosphere is from 5.4 to 57.3 μmol CH₄m^?2 day^?1.     

Extracts of interferon-treated cells can inhibit reticulocyte lysate protein synthesis.

Rumen bacteria retained methanogenic activity when stored at ?60° under H₂. This activity, which resides in $\text{Methanobacterium ruminantium}$ and $\text{Methanobacterium mobilis}$, is not lost when the cells are broken, as has been suggested. Unlike in $\text{Methanosarcina barkerii}$ and $\text{Methanobacterium M.o.H.}$, in rumen bacteria methanogenic enzymes are not soluble but readily precipitated at 15,000 g. Methane was synthesized from tetrahydrofolate derivatives but at slower rates than from CO₂. From the data, it was not possible to determine if methyl- and methylene tetrahydrofolate were oxidized to CO₂ prior to reduction to CH₄. In room light, CH₃-B₁₂ was reduced to CH₄ non-enzymatically in the presence of protein. When the reactions were carried out in the dark, very little CH₄ was formed from CH₃-B₁₂ by rumen bacterial enzymes. The cell-free particulate fraction did not require added ATP for methanogenesis but showed an absolute requirement for H₂.     

Synthesis and antitumor activity of platinum complexes of protonated diamines

Complexes of the formula cis-[Pt(H$\text{N}\text{+}$^～N)(L)Cl₂], where (H$\text{N}\text{+}$^～N) are the protonated diamines including 3-aminoquinuclidine, N-aminopiperidine, piperazine, N-methylpiperazine, 1,1,4-trimethylpiperazine, and N-methyl-1,4-diazabicyclo [2,2,2] octane (N-methyl-dabco) and L = SCN^?, NO₂^?, Br^?, and F^?, were synthesized from the protonated diamine complexes, [Pt(H$\text{N}\text{+}$^～N)Cl₃]. The antitumor activities of the complexes were evaluated in vitro against L1210 murine leukemia cells, and ID₅₀ values for the L-substituted complexes were compared to values of the parent complexes. In each case it was found that replacement of a chloride ion by SCN^?, NO₂^?, Br^?, or F^?, either reduced or completely eliminated antitumor activity. This effect is explained in terms of the trans-directing ability of the ligand, L, compared to chloride. The NO₂-substituted complex of 3- aminoquinuclidine was tested in vivo and found to exhibit little or no antitumor activity.     

Amiloride stimulation of sodium transport in the presence of calcium and a divalent cation chelator

Amiloride in nM to μM concentrations stimulates the short circuit current ($\text{I}{}_{\mathrm{<mtext>sc</mtext>}}$) of the toad urinary bladder by as much as 120% when applied in conjunction with apical Ca²⁺ and a divalent cation chelator. A significant decrease in transepithelial resistance ($\text{R}{}_{\mathrm{<mtext>t</mtext>}}$) is observed simultaneously. This response is spontaneously reversible and its amplitude is dependent upon apical sodium concentrations. The stimulated $\text{I}{}_{\mathrm{<mtext>sc</mtext>}}$ persisted when acetazolamide (1 mM) was introduced, HPO₄^2? substituted for HCO₃^? or SO₄^2? replaced Cl^?. Consequently, the increase in $\text{I}{}_{\mathrm{<mtext>sc</mtext>}}$ is not due to the change of Cl^?, H⁺ or HCO₃^? flux. This behavior in a ‘tight’ epithelium may be related to the mechanism controlling apical sodium permeability.     

Substrate Specificity of Methanogenic Communities from Lake Baikal Bottom Sediments Associated with Hydrocarbon Gas Discharge

Methane production by microbial communities from Lake Baikal bottom sediments with different chemical composition of pore water was studied. Methane production was more active in the media supplemented with H₂: CO₂ and H₂ + CH₃COONa, rather than on media with acetate as the sole source of carbon and energy. Addition of methanol stimulated methane production only in the case of microbial communities from upper silts. Ability of the communities to produce methane correlated reliably with the concentrations of the NO^3–, SO₄^2?, Cl^–, and CH₃COO^– ions in the pore water of the relevant sediments. Cultivation of communities from the mud volcano sediments resulted in development of methanogenic archaea of the family Methanocellaсеае in the media supplemented with H₂: CO₂ and H₂ + CH₃COONa, while methanogenic archaea in the communities cultivated without additional substrates belonged to the genera Methanoregula, Methanobacterium, and Methanosaeta.     

Methane and carbon dioxide dynamics within four vernal pools in Maine,USA

Vernal pools are small, seasonal wetlands that are a common landscape feature contributing to biodiversity in northeastern North American forests. Basic information about their biogeochemical functions, such as carbon cycling, is limited. Concentrations of dissolved methane (CH₄) and carbon dioxide (CO₂) and other water chemistry parameters were monitored weekly at the bottom and surface of four vernal pools in central and eastern Maine, USA, from April to August 2016. The vernal pools were supersaturated with respect to CH₄ and CO₂ at all sampling dates and locations. Concentrations of dissolved CH₄ and CO₂ ranged from 0.4 to 210 μmol L^?1 and 72–2300 μmol L^?1, respectively. Diffusive fluxes of CH₄ and CO₂ into the atmosphere ranged from 0.2 to 73 mmol m^?2 d^?1, and 30–590 mmol m^?2 d^?1, respectively. During the study period, the four vernal pools emitted 0.1–5.8 kg C m^?2 and 9.6–120 kg C m^?2 as CH₄ and CO₂, respectively. The production fluxes (production rates normalized to surface area) of CH₄ and CO₂ ranged from ? 0.02 to 0.66 and 0.40–4.6 g C m^?2 d^?1, respectively, and increased significantly over the season. Methane concentrations were best predicted by alkalinity, ortho-phosphate and depth, while CO₂ concentrations were best predicted with only alkalinity. Alkalinity as a predictor variable highlights the importance of anaerobic respiration in production of both gases. Our study pools had large concentrations and effluxes of CH₄ and CO₂ compared to permanently inundated wetlands, indicating vernal pools are metabolically active sites and may be important contributors to the global carbon budget.     

Mechanism of oxidation of carbon monoxide by bacteria

Double label experiments were performed employing ¹³CO and either H₂¹⁸O or ¹⁸O₂ in the presence of a CO utilizing bacterium. CO₂ generated was trapped and $\text{m}\text{e}$ ratios $\text{47}\text{45}$ showed that the second oxygen atom in the oxidation of CO to CO₂ by this bacterium comes neither from O₂ nor H₂O.     

A Heterogeneous Carbon Nitride–Nickel Photocatalyst for Efficient Low‐Temperature CO2 Methanation

The Sabatier reaction, i.e., the hydrogenation of CO₂ to methane (CH₄) using hydrogen (H₂), constitutes a potentially scalable method to store energy in a product with a high energy density. However, up to today, this reaction has been mainly thermally driven and conducted at high temperatures (typically 400–600 °C). Using light as a renewable energy source will allow for a more sustainable process by lowering the reaction temperature. Here, it is demonstrated that Ni nanoparticles support on graphitic carbon nitride (g‐CN) are a highly efficient and stable photocatalyst for the gas‐phase CO₂ methanation at low temperature (150 °C). Detailed mechanistic studies reveal a very low activation energy for the reaction and high activity under visible light, leading to a remarkable and continuous CH₄ production of 28 µmol g^?1 h^?1 of CH₄ for 24 h.     

Elevated concentrations of CO2 may double methane emissions from mires

The potential impact of an increase in methane emissions from natural wetlands on climate change models could be very large. We report a profound increase in methane emissions from cores of mire peat and vegetation as a direct result of increasing the CO₂ concentration from 355 to 550 μol mol^?1 (a 60% increase). Increased CH₄ fluxes were observed throughout the four month period of study. Seasonal variation in CH₄ flux, consistent with that seen in the field, was observed under both ambient and elevated CO₂. Under ambient CO₂, methane fluxes rose from 0.02 μol m_-2 s^?1 in May to 0.11 μol m^?2 s^?3 in July before declining again in August. Under elevated CO₂ methane fluxes were at least 100% greater throughout the experiment, rising from 0.05 μol m_-2 s^?1 in May to a peak of 0.27 μol m^?2 s^?1 in July. The stimulation of CO₄ emissions was accompanied by a 100% increase in rates of photosynthesis from 4.6 (± 0.3) under ambient CO₂ to 9.3 (± 0.7) μol m^?2 s^?1. Root and shoot biomass were unaffected.     

Energy-coupling mechanisms under aerobic and anaerobic conditions in autotrophically grown Pseudomonas saccharophila

The cell-free preparations from autotrophieally grown Pseudomonas saccharophila catalyzed the process of electron transport from H₂ or various other organic electron donors to either O₂ or NO₃^? with concomitant ATP generation. The respective $\text{P}\text{O}$ ratios with H₂ and NADH were 0.63 and 0.73, the respective $\text{P}\text{NO}{}_3{}^{\mathrm{?}}$ ratios were 0.57 and 0.54. In contrast, the $\text{P}\text{O}$ and $\text{P}\text{NO}{}_3{}^{\mathrm{?}}$ ratios with succinate were 0.18 and 0.11, respectively. ATP formation coupled to the oxidation of ascorbate, in the absence or presence of added N,N,N′,N′-tetramethyl-p-phenylenediamine or cytochrome c, could not be detected. Various uncouplers inhibited phosphorylation with either O₂ or NO₃^? as terminal electron acceptors without affecting the oxidation of H₂ or other substrates. The NADH oxidation at the expense of O₂ or NO₃^? reduction as well as the associated phosphorylation were inhibited by rotenone and amytal. The aerobic and anaerobic H₂ oxidation and coupled ATP synthesis, on the other hand, was unaffected by the flavoprotein inhibitors as well as by the NADH trapping system. The NADH, H₂, and succinate-linked electron transport to O₂ or NO₃^? and the associated phosphorylations were sensitive, however, to antimycin A or 2-n-nonyl-4-hydroxyquino-line-N-oxide, and cyanide or azide. The data indicated that although the phosphorylation sites 1 and II were associated with NADH oxidation by O₂ or NO₃^?, the energy conservation coupled to H₂ oxidation under aerobic or anaerobic conditions appeared to involve site II only.     

Kinetic parameters of human carbonic anhydrase B as determined from NMR linewidths of 13 C in CO 2 and HCO 3 -

The linewidths of the ¹³C NMR signals of CO₂ and $\text{HCO}{}_3{}^{\mathrm{?}}$, in equilibrium aqueous solutions containing small amounts of carbonic anhydrase, are determined mainly by the rate of enzyme-induced interconversion of CO₂ and $\text{HCO}{}_3{}^{\mathrm{?}}$. We have measured these linewidths in unbuffered solutions of human carbonic anhydrase B for several values of [CO₂], at 25°C as a function of pH. From a least-squares analysis of the data, using the equations relating the linewidths to the enzyme kinetics, we have obtained values for the kinetic (Michaelis-Menten) parameters that characterize this interconversion. These preliminary results are in approximate agreement with published values for highly buffered solutions. Additionally, the results confirm that the product of the hydration reaction, and the substrate for the dehydration, is the neutral molecule H₂CO₃.     

Anatomical and enzymic studies of leaves of a C3 × C4Flaveria F1 hybrid exhibiting reduced photorespiration

Flaveria pringlei exhibits C₃ CO₂ compensation concentration (Г) values averaging 53 μl CO₂/l at 21% (v/v) O₂ and 25 ± 2°C. When this species is hybridized with the C₄ species, F. brownii (male) ($\text{Г = 6 μ}\text{l CO}{}_2\text{/}\text{l}$), the F₁ hybrid plants exhibit an average Г value of 31 μl CO₂/l at 21% O₂.Although light micrographs of leaf cross-sections show that the leaves of the hybrid plants possess the mesophyll arrangement characteristic of F. pringlei leaves, the hybrid plants have some bundle-sheath chloroplasts. However, the numbers of these organelles do not appear to be intermediate with respect to the numbers in the parents and are closest to the small number present in the bundle-sheath cells of F. pringlei leaves. The activities of key C₄ enzymes (in μmol · mg Chl^?1 · h^?1) are: phosphoenolpyruvate (PEP) carboxylase, 121; pyruvate, orthophosphate (P_i) dikinase, 26; NADP-malate dehydrogenase, 2529; and NADP-malic enzyme, 82. All of these activities are substantially higher than in F. pringlei, but are only 7–10% of those in F. brownii (with the exception of the NADP-malate dehydrogenase activity). These data suggest that a C₄ cycle might be operating to a limited extent in the hybrid plants resulting in reduced photorespiration.Whether or not C₄ photosynthesis occurs in these hybrid plants, they represent the first reported C₃ × C₄ F₁ hybrids to exhibit reduced Γ-values. This cross and its reciprocal should be useful models for studying the anatomical and biochemical factors determining the development of limited C₄ photosynthesis in C₃ species.     

Effect of N-alkyl-N,N,N-trimethylammonium ions on phosphatidylcholine model membrane structure as studied by 31P-NMR

The interaction of |C_nH_2n+1N⁺(CH₃)₃| · I^? (n = 3, 6, 9, 12, 14, 16 or 18) with egg-yolk phosphatidylcholine-water dispersions has been studied by ³¹P-NMR spectroscopy. It is shown that the effective anisotropy of ³¹P chemical shift (?Δσ_eff) of the lamellar phospholipid liquid-crystalline phase L_α increases with increasing concentration and alkyl chain length of the drug. Addition of $\text{|}\text{C}{}_6\text{H}{}_{13}\text{N}{}^{\mathrm{+}}\text{(CH}{}_3\text{)}{}_3\text{| ·I}{}^{\mathrm{?}}$ or |C₉H₁₉N⁺(CH₃)₃|·I^? to the phospholipid-water dispersion at a molar ratio ammonium salt:phospholipid > 0.8 induces in the dispersion a structure with an effective isotropic phospholipid motion. This structure is unstable and slowly transforms into the hexagonal phase. These effects have not been observed in phospholipid-water dispersions mixed with the ammonium derivatives with the longer alkyl chains n  12, 14, 16 or 18. It is proposed that these results might explain the effects of the investigated drugs on the nerve, muscle and bacterial cells.     

Selective recognition of acetate ion based on fluorescence enhancement chemosensor

Fluorescence study of the complexation between uranyl salophen (L) and some common anions in acetonitrile–water (90:10, v/v) solution showed a tendency of L toward acetate ion (AcO^?). The fluorescence enhancement of L is attributed to a 1:1 complex formation between L and acetate ion which was utilized as the basis for the selective detection of AcO^?. The association constant of the 1:1 complex formation of L–AcO^? was calculated as 6.60 × 10⁶. The linear response range of the fluorescent chemosensor covers a AcO^? concentration range of 1.6 × 10^?7 to 2.5 × 10^?5 mol/L, with a detection limit of 2.5 × 10^?8 mol/L. L showed a selective and sensitive fluorescence enhancement response toward acetate ion over I₃^?, NO₃^?, CN^?, CO₃^2?, Br^?, Cl^?, F^?, H₂PO4^? and SO₄^2?, which was attributed to the higher stability of inorganic complex between acetate and L. Copyright © 2012 John Wiley & Sons, Ltd.     

Valinomycin inhibited methane synthesis in Methanobacteriumthermoautotrophicum

$\text{Methanobacterium}\text{thermoautotrophicum}$ cells, incubated anaerobically under H₂ in 0.1 M KCl or 0.1 M NaCl, above pH 7.5, are interior acid with respect to the incubation medium. The pH gradient thus established can be discharged by either carbonyl cyanide m-chlorophenylhydrazone or valinomycin at high concentration (17μM). In these cells, which actively synthesize CH₄ from CO₂ and H₂, methanogenesis is strongly inhibited when the pH gradient is discharged.     

Respiration-driven proton translocation with nitrite and nitrous oxide in Paracoccus denitrificans

(1) $\text{H}$⁺/electron acceptor ratios have been determined with the oxidant pulse method for cells of denitrifying Paracoccus denitrificans oxidizing endogenous substrates during reduction of O₂, NO^?₂ or N₂O. Under optimal H⁺-translocation conditions, the ratios $\text{H}{}^{\mathrm{+}}\text{O}$, $\text{H}{}^{\mathrm{+}}\text{N}{}_2\text{O}$, $\text{H}{}^{\mathrm{+}}\text{NO}{}^{\mathrm{?}}{}_2$ for reduction to N₂ and $\text{H}{}^{\mathrm{+}}\text{NO}{}^{\mathrm{?}}{}_2$ for reduction to N₂O were 6.0–6.3, 4.02, 5.79 and 3.37, respectively. (2) With ascorbate/N,N,N′,N′-tetramethyl-p-phenylenediamine as exogenous substrate, addition of NO^?₂ or N₂O to an anaerobic cell suspension resulted in rapid alkalinization of the outer bulk medium. $\text{H}{}^{\mathrm{+}}\text{N}{}_2\text{O}$, $\text{H}{}^{\mathrm{+}}\text{NO}{}^{\mathrm{?}}{}_2$ for reduction to N₂ and $\text{H}{}^{\mathrm{+}}\text{NO}{}^{\mathrm{?}}{}_2$ for reduction to N₂O were ?0.84, ?2.33 and ?1.90, respectively. (3) The $\text{H}{}^{\mathrm{+}}\text{oxidant}$ ratios, mentioned in item 2, were not altered in the presence of $\text{valinomycin}\text{K}{}^{\mathrm{+}}$ and the triphenylmethylphosphonium cation. (4) A simplified scheme of electron transport to O₂, NO^?₂ and N₂O is presented which shows a periplasmic orientation of the nitrite reductase as well as the nitrous oxide reductase. Electrons destined for NO^?₂, N₂O or O₂ pass two H⁺-translocating sites. The $\text{H}{}^{\mathrm{+}}\text{electron}$ acceptor ratios predicted by this scheme are in good agreement with the experimental values.     

Methane emissions from sheep pasture,measured with an open‐path eddy covariance system

Methane (CH₄) is an important greenhouse gas, contributing 0.4–0.5 W m^?2 to global warming. Methane emissions originate from several sources, including wetlands, rice paddies, termites and ruminating animals. Previous measurements of methane flux from farm animals have been carried out on animals in unnatural conditions, in laboratory chambers or fitted with cumbersome masks. This study introduces eddy covariance measurements of CH₄, using the newly developed LI‐COR LI‐7700 open‐path methane analyser, to measure field‐scale fluxes from sheep grazing freely on pasture. Under summer conditions, fluxes of methane in the morning averaged 30 nmol m^?2 s^?1, whereas those in the afternoon were above 100 nmol m^?2 s^?1, and were roughly two orders of magnitude larger than the small methane emissions from the soil. Methane emissions showed no clear relationship with air temperature or photosynthetically active radiation, but some diurnal pattern was apparent, probably linked to sheep grazing behaviour and metabolism. Over the measurement period (days 60–277, year 2010), cumulative methane fluxes were 0.34 mol CH₄ m^?2, equating to 134.3 g CO₂ equivalents m^?2. By comparison, a carbon dioxide (CO₂) sink of 819 g CO₂ equivalents m^?2 was measured over the same period, but it is likely that much of this would be released back to the atmosphere during the winter or as off‐site losses (through microbial and animal respiration). By dividing methane fluxes by the number of sheep in the field each day, we calculated CH₄ emissions per head of livestock as 7.4 kg CH₄ sheep^?1 yr^?1, close to the published IPCC emission factor of 8 kg CH₄ sheep^?1 yr^?1.