首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Extra virgin olive oil (EVOO) and olives, key sources of unsaturated fatty acids in the Mediterranean diet, provide health benefits to humans. Nitric oxide (•NO) and nitrite (NO2 )-dependent reactions of unsaturated fatty acids yield electrophilic nitroalkene derivatives (NO2-FA) that manifest salutary pleiotropic cell signaling responses in mammals. Herein, the endogenous presence of NO2-FA in both EVOO and fresh olives was demonstrated by mass spectrometry. The electrophilic nature of these species was affirmed by the detection of significant levels of protein cysteine adducts of nitro-oleic acid (NO2-OA-cysteine) in fresh olives, especially in the peel. Further nitration of EVOO by NO2 under acidic gastric digestive conditions revealed that human consumption of olive lipids will produce additional nitro-conjugated linoleic acid (NO2-cLA) and nitro-oleic acid (NO2-OA). The presence of free and protein-adducted NO2-FA in both mammalian and plant lipids further affirm a role for these species as signaling mediators. Since NO2-FA instigate adaptive anti-inflammatory gene expression and metabolic responses, these redox-derived metabolites may contribute to the cardiovascular benefits associated with the Mediterranean diet.  相似文献   

2.
Electrophilic fatty acid nitroalkenes (NO2-FA) are products of nitric oxide and nitrite-mediated unsaturated fatty acid nitration. These electrophilic products induce pleiotropic signaling actions that modulate metabolic and inflammatory responses in cell and animal models. The metabolism of NO2-FA includes reduction of the vinyl nitro moiety by prostaglandin reductase-1, mitochondrial β-oxidation, and Michael addition with low molecular weight nucleophilic amino acids. Complex lipid reactions of fatty acid nitroalkenes are not well defined. Herein we report the detection and characterization of NO2-FA-containing triacylglycerides (NO2-FA-TAG) via mass spectrometry-based methods. In this regard, unsaturated fatty acids of dietary triacylglycerides are targets for nitration reactions during gastric acidification, where NO2-FA-TAG can be detected in rat plasma after oral administration of nitro-oleic acid (NO2-OA). Furthermore, the characterization and profiling of these species, including the generation of beta oxidation and dehydrogenation products, could be detected in NO2-OA-supplemented adipocytes. These data revealed that NO2-FA-TAG, formed by either the direct nitration of esterified unsaturated fatty acids or the incorporation of nitrated free fatty acids into triacylglycerides, contribute to the systemic distribution of these reactive electrophilic mediators and may serve as a depot for subsequent mobilization by lipases to in turn impact adipocyte homeostasis and tissue signaling events.  相似文献   

3.
The oxidation and nitration of unsaturated fatty acids transforms cell membrane and lipoprotein constituents into mediators that regulate signal transduction. The formation of 9-NO2-octadeca-9,11-dienoic acid and 12-NO2-octadeca-9,11-dienoic acid stems from peroxynitrite- and myeloperoxidase-derived nitrogen dioxide reactions as well as secondary to nitrite disproportionation under the acidic conditions of digestion. Broad anti-inflammatory and tissue-protective responses are mediated by nitro-fatty acids. It is now shown that electrophilic fatty acid nitroalkenes are present in the urine of healthy human volunteers (9.9 ± 4.0 pmol/mg creatinine); along with electrophilic 16- and 14-carbon nitroalkenyl β-oxidation metabolites. High resolution mass determinations and coelution with isotopically-labeled metabolites support renal excretion of cysteine-nitroalkene conjugates. These products of Michael addition are in equilibrium with the free nitroalkene pool in urine and are displaced by thiol reaction with mercury chloride. This reaction increases the level of free nitroalkene fraction >10-fold and displays a KD of 7.5 × 10−6 M. In aggregate, the data indicates that formation of Michael adducts by electrophilic fatty acids is favored under biological conditions and that reversal of these addition reactions is critical for detecting both parent nitroalkenes and their metabolites. The measurement of this class of mediators can constitute a sensitive noninvasive index of metabolic and inflammatory status.  相似文献   

4.
The oxidation and nitration of unsaturated fatty acids by oxides of nitrogen yield electrophilic derivatives that can modulate protein function via post-translational protein modifications. The biological mechanisms accounting for fatty acid nitration and the specific structural characteristics of products remain to be defined. Herein, conjugated linoleic acid (CLA) is identified as the primary endogenous substrate for fatty acid nitration in vitro and in vivo, yielding up to 105 greater extent of nitration products as compared with bis-allylic linoleic acid. Multiple enzymatic and cellular mechanisms account for CLA nitration, including reactions catalyzed by mitochondria, activated macrophages, and gastric acidification. Nitroalkene derivatives of CLA and their metabolites are detected in the plasma of healthy humans and are increased in tissues undergoing episodes of ischemia reperfusion. Dietary CLA and nitrite supplementation in rodents elevates NO2-CLA levels in plasma, urine, and tissues, which in turn induces heme oxygenase-1 (HO-1) expression in the colonic epithelium. These results affirm that metabolic and inflammatory reactions yield electrophilic products that can modulate adaptive cell signaling mechanisms.  相似文献   

5.
The uptake rates of different nitrogen (N) forms (NO3, urea, and the amino acids glycine and glutamic acid) by N-deficient, laboratory-grown cells of the mixotrophic haptophyte, Prymnesium parvum, were measured and the preference by the cells for the different forms determined. Cellular N uptake rates (ρcell, fmol N cell−1 h−1) were measured using 15N-labeled N substrates. P. parvum showed high preference for the tested amino acids, in particular glutamic acid, over urea and NO3 under the culture nutrient conditions. However, extrapolating these rates to Baltic Seawater summer conditions, P. parvum would be expected to show higher uptake rates of NO3 and the amino acids relative to urea because of the difference in average concentrations of these substrates. A high uptake rate of glutamic acid at low substrate concentrations suggests that this substrate is likely used through extracellular enzymes. Nitrate, urea and glycine, on the other hand, showed a non-saturating uptake over the tested substrate concentration (1–40 μM-N for NO3 and urea, 0.5–10 μM-N for glycine), indicating slower membrane-transport rates for these substrates.  相似文献   

6.
Halothane (CF3CHClBr), a widely used volatile anesthetic, undergoes extensive biotransformation in humans. Oxidative halothane metabolism yields the stable metabolites trifluoroacetic acid and bromide which can be detected in plasma and urine. To date, analytical methodologies have either required extensive sample preparation, or two separate analytical procedures to determine plasma and urine concentrations of these analytes. A rapid and sensitive method utilizing high-performance liquid chromatography-ion chromatography (HPLC-IC) with suppressed conductivity detection was developed for the simultaneous detection of both trifluoroacetic acid and bromide in plasma and urine. Sample preparation required only ultrafiltration. Standard curves were linear (r2≥0.99) from 10 to 250 μM trifluoroacetic acid and 2 to 5000 μM bromide in plasma and 10 to 250 μM trifluoroacetic acid and 2 to 50 μM bromide in urine. The assay was applied to quantification of trifluoroacetic acid and bromide in plasma and urine of a patient undergoing halothane anesthesia.  相似文献   

7.
1. We investigated diurnal nitrate (NO3) concentration variability in the San Joaquin River using an in situ optical NO3 sensor and discrete sampling during a 5‐day summer period characterized by high algal productivity. Dual NO3 isotopes (δ15NNO3 and δ18ONO3) and dissolved oxygen isotopes (δ18ODO) were measured over 2 days to assess NO3 sources and biogeochemical controls over diurnal time‐scales. 2. Concerted temporal patterns of dissolved oxygen (DO) concentrations and δ18ODO were consistent with photosynthesis, respiration and atmospheric O2 exchange, providing evidence of diurnal biological processes independent of river discharge. 3. Surface water NO3 concentrations varied by up to 22% over a single diurnal cycle and up to 31% over the 5‐day study, but did not reveal concerted diurnal patterns at a frequency comparable to DO concentrations. The decoupling of δ15NNO3 and δ18ONO3 isotopes suggests that algal assimilation and denitrification are not major processes controlling diurnal NO3 variability in the San Joaquin River during the study. The lack of a clear explanation for NO3 variability likely reflects a combination of riverine biological processes and time‐varying physical transport of NO3 from upstream agricultural drains to the mainstem San Joaquin River. 4. The application of an in situ optical NO3 sensor along with discrete samples provides a view into the fine temporal structure of hydrochemical data and may allow for greater accuracy in pollution assessment.  相似文献   

8.
《Biomass》1988,15(4):249-257
An experiment was conducted in the growth chamber to quantify the biomass production, N removal and N2 fixation from a synthetic medium by Chlamydomonas reinhardtii and Anabaena flos-aquae. Nitrogen was supplied at a concentration of 100 mg liter−1 of NO315N and NH4+15 (3·5 atom %), respectively. After 21 days Chlamydomonas reinhardtii removed an average of 83·8 and 78·7 mg N liter−1 as NO3 and NH4+, respectively. Averages of 0·89 and 0·71 g liter−1 (first batch), 1·63 and 0·95 g liter (second batch) algal biomass were collected from NO3 and NH4+ media, respectively. Uptake rates of 0·11 mg 15N g−1 algae day−1 from NO3 medium and 0·10 mg 15N g−1 algae day−1 from NH4+ medium were calculated. Algal cells grown in NO3 and NH4+ medium contained 71 and 65 g N kg−1 (first batch), 39 and 58 g N kg−1 (second batch), respectively. Anabaena flos-aquae produced averages of 0·58 and 0·46 g liter−1 (first batch), 0·55 and 0·48 g liter−1 (second batch) after 14 days of growth from NO3 and NH4+ media, respectively. Blue-green algal biomass contained higher N (81–98 g kg−1) than green algae. Isotope dilution method for determining N2 fixation indicated that 55% and 77% of total N of blue-green algae grown in NO3 and NH4+ media, respectively, was derived from the atmosphere.  相似文献   

9.
15-Hydroxyprostaglandin dehydrogenase (15PGDH) is the primary enzyme catalyzing the conversion of hydroxylated arachidonic acid species to their corresponding oxidized metabolites. The oxidation of hydroxylated fatty acids, such as the conversion of prostaglandin (PG) E2 to 15-ketoPGE2, by 15PGDH is viewed to inactivate signaling responses. In contrast, the typically electrophilic products can also induce anti-inflammatory and anti-proliferative responses. This study determined that hydroxylated docosahexaenoic acid metabolites (HDoHEs) are substrates for 15PGDH. Examination of 15PGDH substrate specificity was conducted in cell culture (A549 and primary human airway epithelia and alveolar macrophages) using chemical inhibition and shRNA knockdown of 15PGDH. Substrate specificity is broad and relies on the carbon position of the acyl chain hydroxyl group. 14-HDoHE was determined to be the optimal DHA substrate for 15PGDH, resulting in the formation of its electrophilic metabolite, 14-oxoDHA. Consistent with this, 14-HDoHE was detected in bronchoalveolar lavage cells of mild to moderate asthmatics, and the exogenous addition of 14-oxoDHA to primary alveolar macrophages inhibited LPS-induced proinflammatory cytokine mRNA expression. These data reveal that 15PGDH-derived DHA metabolites are biologically active and can contribute to the salutary signaling actions of Ω-3 fatty acids.  相似文献   

10.
  • 1.1. In the presence of insulin, 10−5 M 3,3',5-triiodothyronine (T3) treatment for 1/2 hr decreased fatty acid synthesis 35% only in adipocytes from lean rats, whereas at 10−11 M through 10−7M T3 the obese adipocytes had nearly a 20% increase in fatty acid synthesis.
  • 2.2. A 2 hr pretreatment of adipocytes with 10−9 and 10−7 M T3 decreased insulin-stimulated fatty acid synthesis by nearly 20% in both lean and obese adipocytes.
  • 3.3. In the absence of insulin, the 2 hr pretreatment with 10−9 M T3 resulted in a 45% increase in lean adipocyte fatty acid synthesis, though the obese adipocytes required at least 10−7 M T3 for 2 hr to increase the non-insulin-stimulated fatty acid synthesis by 50%.
  • 4.4. At 10−9M T3 concentrations non-insulin-stimulated fatty acid synthesis was increased by 200% in lean adipose tissue explants, but obese adipose expiants were not significantly affected under these conditions.
  • 5.5. The addition of 10−9 M T3 plus insulin to the explant media decreased fatty acid synthesis by 35% in both the lean and obese tissues.
  • 6.6. The results also imply that the low T3 status of the obese rat may be contributory to the elevated fatty acid synthesis observed in obese adipocytes.
  相似文献   

11.
Abstract. Nitrate uptake into Chara corallina cells at different external pH (pHo) after different NO3 pretreatment conditions has been investigated. Following NO3 pretreatment (0.2 mol m−3 NO3) there was little effect of pHo on subsequent net NO3 uptake into Chara cells. After N deprivation (2 mmol m−3 NO3) there was a pronounced effect of pHo on nitrate uptake, the maximum rate occurring at pHo 4.7. There was no consistent relationship between OH efflux and NO3 uptake in short term experiments (< 1 h). NO3 efflux was also sensitive to pHo, the maximum rate occurring at ∼ pHo 5.0. An inhibitor of the proton pump, DES, immediately stimulated NO3 uptake into cells pretreated with NO3 and prevented the time-dependent decrease in NO3, uptake into Chara cells that had been previously treated with low N (2 mmol m−3 NO3). NO3 efflux was found to be very sensitive to DES with Ki= 0.7 mmol m−3. At the optimum pHo for NO3 uptake the effect of DES on membrane potential (ψm) were slight, and only apparent after 30 min. The results are interpreted in context of current models relating NO3 uptake and H+ pump activity. A new model for NO3 uptake is proposed which involves NO3/NO3 exchange at steady state.  相似文献   

12.
In M. braunii, the uptake of NO3 and NO2 is blue-light-dependent and is associated with alkalinization of the medium. In unbuffered cell suspensions irradiated with red light under a CO2-free atmosphere, the pH started to rise 10s after the exposure to blue light. When the cellular NO3 and NO2 reductases were active, the pH increased to values of around 10, since the NH4+ generated was released to the medium. When the blue light was switched off, the pH stopped increasing within 60 to 90s and remained unchanged under background red illumination. Titration with H2SO4 of NO3 or NO2 uptake and reduction showed that two protons were consumed for every one NH4+ released. The uptake of Cl was also triggered by blue light with a similar 10 s time response. However, the Cl -dependent alkalinization ceased after about 3 min of blue light irradiation. When the blue light was turned off, the pH immediately (15 to 30 s) started to decline to the pre-adjusted value, indicating that the protons (and presumably the Cl) taken up by the cells were released to the medium. When the cells lacked NO3 and NO2 reductases, the shape of the alkalinization traces in the presence of NO3 and NO2 was similar to that in the presence of Cl, suggesting that NO3 or NO2 was also released to the medium. Both the NO3 and Cl-dependent rates of alkalinization were independent of mono- and divalent cations.  相似文献   

13.
Nitric oxide (NO) is a chemical weapon within the arsenal of immune cells, but is also generated endogenously by different bacteria. Pseudomonas aeruginosa are pathogens that contain an NO-generating nitrite (NO2) reductase (NirS), and NO has been shown to influence their virulence. Interestingly, P. aeruginosa also contain NO dioxygenase (Fhp) and nitrate (NO3) reductases, which together with NirS provide the potential for NO to be metabolically cycled (NO→NO3→NO2→NO). Deeper understanding of NO metabolism in P. aeruginosa will increase knowledge of its pathogenesis, and computational models have proven to be useful tools for the quantitative dissection of NO biochemical networks. Here we developed such a model for P. aeruginosa and confirmed its predictive accuracy with measurements of NO, O2, NO2, and NO3 in mutant cultures devoid of Fhp or NorCB (NO reductase) activity. Using the model, we assessed whether NO was metabolically cycled in aerobic P. aeruginosa cultures. Calculated fluxes indicated a bottleneck at NO3, which was relieved upon O2 depletion. As cell growth depleted dissolved O2 levels, NO3 was converted to NO2 at near-stoichiometric levels, whereas NO2 consumption did not coincide with NO or NO3 accumulation. Assimilatory NO2 reductase (NirBD) or NorCB activity could have prevented NO cycling, and experiments with ΔnirB, ΔnirS, and ΔnorC showed that NorCB was responsible for loss of flux from the cycle. Collectively, this work provides a computational tool to analyze NO metabolism in P. aeruginosa, and establishes that P. aeruginosa use NorCB to prevent metabolic cycling of NO.  相似文献   

14.
Nitrated derivatives of fatty acids (NO2-FA) are pluripotent cell-signaling mediators that display anti-inflammatory properties. Current understanding of NO2-FA signal transduction lacks insight into how or if NO2-FA are modified or metabolized upon formation or administration in vivo. Here the disposition and metabolism of nitro-9-cis-octadecenoic (18:1-NO2) acid was investigated in plasma and liver after intravenous injection in mice. High performance liquid chromatography-tandem mass spectrometry analysis showed that no 18:1-NO2 or metabolites were detected under basal conditions, whereas administered 18:1-NO2 is rapidly adducted to plasma thiol-containing proteins and glutathione. NO2-FA are also metabolized via β-oxidation, with high performance liquid chromatography-tandem mass spectrometry analysis of liver lipid extracts of treated mice revealing nitro-7-cis-hexadecenoic acid, nitro-5-cis-tetradecenoic acid, and nitro-3-cis-dodecenoic acid and corresponding coenzyme A derivatives of 18:1-NO2 as metabolites. Additionally, a significant proportion of 18:1-NO2 and its metabolites are converted to nitroalkane derivatives by saturation of the double bond, and to a lesser extent are desaturated to diene derivatives. There was no evidence of the formation of nitrohydroxyl or conjugated ketone derivatives in organs of interest, metabolites expected upon 18:1-NO2 hydration or nitric oxide (•NO) release. Plasma samples from treated mice had significant extents of protein-adducted 18:1-NO2 detected by exchange to added β-mercaptoethanol. This, coupled with the observation of 18:1-NO2 release from glutathione-18:1-NO2 adducts, supports that reversible and exchangeable NO2-FA-thiol adducts occur under biological conditions. After administration of [3H]18:1-NO2, 64% of net radiolabel was recovered 90 min later in plasma (0.2%), liver (18%), kidney (2%), adipose tissue (2%), muscle (31%), urine (6%), and other tissue compartments, and may include metabolites not yet identified. In aggregate, these findings show that electrophilic FA nitroalkene derivatives (a) acquire an extended half-life by undergoing reversible and exchangeable electrophilic reactions with nucleophilic targets and (b) are metabolized predominantly via saturation of the double bond and β-oxidation reactions that terminate at the site of acyl-chain nitration.The reaction of unsaturated fatty acids with nitric oxide (•NO)- and nitrite species, including nitrogen dioxide (•NO2), peroxynitrite (ONOO), and nitrous acid (HNO2), yields a complex array of oxidized and nitrated products (14). The mechanisms of biological fatty acid nitration, the structural isomer distribution of nitrated fatty acids (NO2-FAs)2 and the signaling actions of specific NO2-FA regioisomers remain incompletely characterized. Current data reveal that, during fatty acid oxidation and nitration, vinyl nitro regioisomers represent a component of these products that display distinctive chemical reactivities and receptor-dependent signaling actions. Here, we investigate the metabolic fate of the nitroalkene derivative of oleic acid (1, 2).Unsaturated fatty acid nitration was first described in model studies of air-pollutant-induced lipid oxidation where lipids were exposed to high concentrations of •NO2 (5, 6). More recently nitrated unsaturated fatty acids have been reported as products of acidic reactions of , radical chain termination reactions induced by •NO (710), and the oxidation of to •NO2 by the leukocyte-derived enzyme myeloperoxidase (1). Various mechanisms can mediate the formation of nitroalkene derivatives of unsaturated fatty acids (11), including homolytic attack of •NO2 (12), reaction of •NO2 with a pre-existing fatty acid carbon-centered radical (2, 13), and the protonation of nitrite under acidic conditions (pH 5.5 and lower) to yield an array of HNO2-derived nitrating species (3, 14). The conditions promoting fatty acid nitration by •NO and species (low oxygen tension, radical formation, and low pH) are not expected to be broadly distributed systemically (e.g. in plasma or extracellular fluids). Rather, nitration reactions will preferably occur during inflammatory or metabolic stress in microenvironments such as the intermembrane space of mitochondria, the low pH environment of the digestive tract, and activated macrophage and neutrophil-rich compartments. Moreover, the acidic, replete and low O2 tension conditions that promote nitration reactions are characteristic of inflammatory loci. Although multiple reactions leading to accelerated formation of nitrating species occur at specific anatomic sites, plasma levels of nitrated fatty acids are expected to be low due to events described herein.Robust electrophilic reactivity and avid nuclear lipid receptor ligand activity have conferred to the class of fatty acid nitroalkene derivatives potent anti-inflammatory properties that occur predominantly via non-cGMP-dependent mechanisms. Nitro derivatives of oleic and linoleic acid inhibit leukocyte and platelet activation (15), vascular smooth muscle proliferation (16), lipopolysaccharide-stimulated macrophage cytokine secretion (17), activate peroxisome proliferator-activated receptor-γ (1, 18), and induce endothelial heme oxygenase 1 expression (19). NO2-FA also potently modulate nuclear factor-erythroid 2-related factor 2/Kelch-like ECH-associating protein 1 (Nrf2/Keap1) (16, 17) and nuclear factor κB (NFκB)-regulated inflammatory signaling (17). Previous observations of the •NO-mediated, cGMP-dependent vessel relaxation induced by NO2-FA were made under serum- and lipid-free conditions. More recently, it has been appreciated that micellar and membrane stabilization of NO2-FA prevents Nef-like aqueous decay reactions and consequent •NO release, supporting that the predominant signaling actions mediated by NO2-FA are •NO and cGMP-independent (20, 21).Current data indicate that electrophilic adduction of biological targets primarily accounts for NO2-FA signal transduction. The high electronegativity of NO2 substituents, when bound to an alkenyl carbon of fatty acids, confers an electrophilic nature to the adjacent β-carbon and enables Michael addition reaction with nucleophiles such as protein His and Cys residues. This process, termed nitroalkylation (22), results in the clinically detectable and reversible adduction of the nucleophilic thiol of glutathione (GSH) and both cysteine and histidine residues of glyceraldehyde-3-phosphate dehydrogenase (23). Furthermore, inhibition of NFκB signaling occurs via nitroalkylation of p65 subunit thiols (17), and recent findings reveal that NO2-FA activation of peroxisome proliferator-activated receptor-γ is uniquely induced by covalent nitroalkylation of the ligand binding domain Cys-285.3Multiple reports support the endogenous generation and presence of nitrated fatty acids (1, 24), first observed in bovine papillary muscles as a vicinal nitrohydroxyeicosatetraenoic acid (25). Nitrolinoleate has been detected in human blood plasma and cholesteryl nitrolinoleate in human plasma and lipoproteins (4, 26), with hyperlipidemic and post-prandial conditions elevating plasma levels of NO2-FA. Further support for the inflammatory generation of NO2-FA comes from lipopolysaccharide and interferon-γ-activated murine J774.1 macrophages, where increased nitration of the acyl chain of cholesteryl linoleate was paralleled by increased macrophage expression and activity of nitric-oxide synthase 2 (27).To date, insight into the mechanisms of nitroalkene signaling actions overshadows knowledge of the generation, trafficking, and metabolism of nitroalkenes in vivo. Appreciating that NO2-FA derivatives are detectable clinically, and that their levels increase following •NO-dependent oxidative reactions (4, 28), challenges still exist in their routine detection. Because the in vivo administration of NO2-FA may exert anti-inflammatory benefit, the disposition and metabolite profiles of these species in vivo is of relevance. Here we report that only 2.4% of nitrooctadecenoic acid (18:1-NO2) is immediately detectable in the vascular compartment as native 18:1-NO2 upon intravenous injection in mice, with the remaining pool of 18:1-NO2 (a) reversibly bound to plasma and tissue thiols via Michael addition; (b) metabolized to nitro-octadecanoic acid (18:0-NO2) and nitro-octadecadienoic acid (18:2-NO2); and (c) catabolized by hepatic β-oxidation following thioester formation with coenzyme A.  相似文献   

15.
A network of long-term monitoring sites on nitrogen (N) input and output of forests across Germany showed that a number of Germany's forests are subject to or are experiencing N saturation and that spruce (Picea abies) stands have high risk. Our study was aimed at (1) quantifying the changes in gross rates of microbial N cycling and retention processes in forest soils along an N enrichment gradient and (2) relating the changes in soil N dynamics to N losses. We selected spruce sites representing an N enrichment gradient (indicated by leaching : throughfall N ratios) ranging from 0.04–0.13 (low N),≤0.26 (intermediate N enrichment) to≥0.42 (highly N enriched). To our knowledge, our study is the first to report on mechanistic changes in gross rates of soil N cycling and abiotic NO3 retention under ambient N enrichment gradient. Gross N mineralization, NH4+ immobilization, gross nitrification, and NO3 immobilization rates increased up to intermediate N enrichment level and somewhat decreased at highly N-enriched condition. The turnover rates of NH4+ and microbial N pools increased while the turnover rates of the NO3 pool decreased across the N enrichment gradient. Abiotic immobilization of NH4+ did not differ across sites and was lower than that of NO3. Abiotic NO3 immobilization decreased across the N enrichment gradient. Microbial assimilation and turnover appeared to contribute largely to the retention of NH4+. The increasing NO3 deposition and decreasing turnover rates of the NO3 pool, combined with decreasing abiotic NO3 retention, possibly contributed to increasing NO3 leaching and gaseous emissions across the N enrichment gradient. The empirical relationships of changes in microbial N cycling across the N enrichment gradient may be integrated in models used to predict responses of forest ecosystems (e.g. spruce) to increasing N deposition.  相似文献   

16.
Nitrogen-14 and nitrogen-15 nuclear magnetic resonance (NMR) spectra were recorded for freshly dissected buds of Picea glauca and for buds grown for 3, 6 and 9 weeks on shoot-forming medium. Resonances for Glu (and other αNH2 groups), Pro, Ala, and the side chain groups in Gln, Arg, Orn, and γ-aminobutyric acid could be detected in in vivo15N NMR spectra. Peaks for α-amino groups, Pro, NO3 and NH4+ could also be identified in 14N NMR spectra. Perfusion experiments performed for up to 20 hours in the NMR spectrometer showed that 15N-labeled NH4+ and NO3 are first incorporated into the amide group of Gln and then in the αNH2 pool. Subsequently, it also emerges in Ala and Arg. These data suggest that the glutamine synthetase/ glutamate synthase pathway functions under these conditions. The assimilation of NH4+ is much faster than that of NO3. Consequently after 10 days of growth more than 70% of the newly synthesized internal free amino acid pool derives its nitrogen from NH4+ rather than NO3. If NH4+ is omitted from the medium, no NO3 is taken up during 9 weeks and the buds support limited growth by utilizing their endogenous amino acid pools. It is concluded that NH4+ and NO3 are both required for the induction of nitrate- and nitrite reductase.  相似文献   

17.
Isolated frog gastric mucosa was used to study the separation of formation of protons (or their precursors) from proton translocation by using various inhibitors. Both thiocyanate (SCN) and nitrite (NO2) inhibit the acid secretion in spontanously secreting mucosa. The inhibition is reversed when the inhibitor is removed such that the excess acid secreted above baseline in the ‘off’-period compensates for the amount inhibited in the ‘on’-period. Both agents also inhibit the effect on acid secretion of pulse stimulation with histamine though to a lesser extent. Upon removal of the inhibitor, the total amount of acid secreted in excess of basal is equal to that observed with histamine alone. Likewise, metiamide, an H2-antagonist, also inhibits acid secretion with or without histamine. However, in contrast to SCN and NO2, removal of this inhibitor is without effect on the acid-secretion rate. These results indicate that both SCN and NO2 inhibit the proton translocation rather than the formation of protons or their precursors as is the case with metiamide.  相似文献   

18.
A new automated system for the analysis of nitrate via reduction with a high-pressure cadmium column is described. Samples of urine, saliva, deproteinized plasma, gastric juice, and milk can be analyzed for nitrate, nitrite, or both with a lower limit of detection of 1.0 nmol NO3? or NO2?/ml. The system allows quantitative reduction of nitrate and automatically eliminates interference from other compounds normally present in urine and other biological fluids. Analysis rate is 30 samples per hour, with preparation for most samples limited to simple dilution with distilled water. The application of gas chromatography/mass spectrometry for the analysis of 15NO3? in urine after derivatization to 15NO2-benzene is also described.  相似文献   

19.
Reactive oxygen species mediate a decrease in nitric oxide (NO) bioavailability and endothelial dysfunction, with secondary oxidized and nitrated by-products of these reactions contributing to the pathogenesis of numerous vascular diseases. While oxidized lipids and lipoproteins exacerbate inflammatory reactions in the vasculature, in stark contrast the nitration of polyunsaturated fatty acids and complex lipids yields electrophilic products that exhibit pluripotent anti-inflammatory signaling capabilities acting via both cGMP-dependent and -independent mechanisms. Herein we report that nitro-oleic acid (OA-NO2) treatment increases expression of endothelial nitric oxide synthase (eNOS) and heme oxygenase 1 (HO-1) in the vasculature, thus transducing vascular protective effects associated with enhanced NO production. Administration of OA-NO2 via osmotic pump results in a significant increase in eNOS and HO-1 mRNA in mouse aortas. Moreover, HPLC-MS/MS analysis showed that NO2-FAs are rapidly metabolized in cultured endothelial cells (ECs) and treatment with NO2-FAs stimulated the phosphorylation of eNOS at Ser1179. These posttranslational modifications of eNOS, in concert with elevated eNOS gene expression, contributed to an increase in endothelial NO production. In aggregate, OA-NO2-induced eNOS and HO-1 expression by vascular cells can induce beneficial effects on endothelial function and provide a new strategy for treating various vascular inflammatory and hypertensive disorders.  相似文献   

20.
Nitrogen dioxide is formed endogenously via the oxidation of NO by O2 or O2 and from NO2 via peroxidases, among other pathways. This radical has many potential biological targets and its concentration, like that of NO and other reactive nitrogen species, is thought to be elevated at sites of inflammation. To investigate the specific cytotoxic or mutagenic effects of NO2, it is desirable to be able to maintain its concentration at constant, predictable, and physiological levels in cell cultures, in the absence of NO. To do this, a delivery system was constructed in which NO2-containing gas mixtures contact a liquid within a small (110 ml) stirred reactor. In such gas mixtures NO2 is present in equilibrium with its dimer, N2O4. The uptake of NO2 and N2O4 was characterized by measuring the accumulation rates of NO2 and NO3, the stable products of N2O4 hydrolysis, in buffered aqueous solutions. In some experiments NO2-reactive 2,2′-azino-bis(3-ethyl-benzothiazoline-6-sulfonate) (ABTS) was included and formation of the stable ABTS radical was measured. A reaction–diffusion model was developed that predicts the accumulation rates of all three products to within 15% for gas-phase concentrations of NO2 spanning 3 orders of magnitude. The model also provides estimates for the NO2 concentration in the liquid. This system should be useful for exposing cells to NO2 concentrations similar to those in vivo.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号