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1.
In this study, we show that boronates, a class of synthetic organic compounds, react rapidly and stoichiometrically with peroxynitrite (ONOO) to form stable hydroxy derivatives as major products. Using a stopped-flow kinetic technique, we measured the second-order rate constants for the reaction with ONOO, hypochlorous acid (HOCl), and hydrogen peroxide (H2O2) and found that ONOO reacts with 4-acetylphenylboronic acid nearly a million times (k = 1.6 × 106 M− 1 s− 1) faster than does H2O2 (k = 2.2 M− 1 s− 1) and over 200 times faster than does HOCl (k = 6.2 × 103 M− 1 s− 1). Nitric oxide and superoxide together, but not alone, oxidized boronates to the same phenolic products. Similar reaction profiles were obtained with other boronates. Results from this study may be helpful in developing a novel class of fluorescent probes for the detection and imaging of ONOO formed in cellular and cell-free systems.  相似文献   

2.
A sensitive, selective, and rapid enzymatic method is proposed for the quantification of hydrogen peroxide (H2O2) using 3-methyl-2-benzothiazolinonehydrazone hydrochloride (MBTH) and 10,11-dihydro-5H-benz(b,f)azepine (DBZ) as chromogenic cosubstrates catalyzed by horseradish peroxidase (HRP) enzyme. MBTH traps free radical released during oxidation of H2O2 by HRP and gets oxidized to electrophilic cation, which couples with DBZ to give an intense blue-colored product with maximum absorbance at 620 nm. The linear response for H2O2 is found between 5 × 10−6 and 45 × 10−6 mol L−1 at pH 4.0 and a temperature of 25 °C. Catalytic efficiency and catalytic power of the commercial peroxidase were found to be 0.415 × 106 M−1 min−1 and 9.81 × 10−4 min−1, respectively. The catalytic constant (kcat) and specificity constant (kcat/Km) at saturated concentration of the cosubstrates were 163.2 min−1 and 4.156 × 106 L mol−1 min−1, respectively. This method can be incorporated into biochemical analysis where H2O2 undergoes catalytic oxidation by oxidase. Its applicability in the biological samples was tested for glucose quantification in human serum.  相似文献   

3.
Mouse peritoneal macrophages activated by bacillus Calmette-Guerin (BCG) were incubated with human α2-macroglobulin converted to its ‘fast’ form with either trypsin or methylamine before being stimulated with phorbol myrystate acetate. Both α2-macroglobulin-trypsin and α2-macroglobulin-methylamine inhibited macrophage production of superoxide anion (O2) while native α2-macroglobulin had little effect except at high concentration. The α2-macroglobulin ‘fast’ forms, which bind with a Kd of about 8 nM, inhibited 50% generation of O2(ID50) at a concentration of 7 nM while α2-macroglobulin inhibited O2 production with an ID50 of 141 nM. The ‘fast’ forms of α2-macroglobulin may play a role in the feedback regulation of inflammatory reactions.  相似文献   

4.
A biotinylated mannotriose (Man3-bio) was dispersively immobilized in the matrix of biotinylated lactose (Gal-Glc-bio) on a streptavidin-covered, 27-MHz quartz crystal microbalance (QCM), and binding kinetics of concanavalin A (Con A) to Man3-bio in the Gal-Glc-bio matrix could be obtained from frequency decreases (mass increases) of the QCM. Association constants (Ka) and binding and dissociation rate constants (kon and koff) could be determined separately as the 1:1 and 1:2 bindings of Con A to Man3-bio on the surface. When Man3-bio was immobilized with content of 1 to 5 mol% in the matrix, the 1:1 binding of Con A to Man3-bio was obtained as Ka = (4 ± 1) × 106 M−1, kon = (4 ± 1) × 104 M−1 s−1, and koff = (12 ± 2) × 10–3 s−1. On the contrary, when Man3-bio was immobilized with content of 20 to 100 mol% in the matrix, the 1:2 binding of Con A to Man3-bio was obtained as Ka = (14 ± 2) × 106 M−1, kon = (14 ± 2) × 104 M−1 s−1, and koff = (7 ± 2) × 10–3 s−1. Thus, Ka for the 1:2 binding was 10 times larger than that for the 1:1 binding, with a three times larger binding rate constant (kon) and a three times smaller dissociation rate constant (koff). This is the first example to obtain separate kinetic parameters for the 1:1 and 1:2 bindings of lectins to carbohydrates on the surface.  相似文献   

5.
A lectin recognizing D-galactose was purified from the pacific annelid Perinereis nuntia ver. vallata (Polychaeta) by affinity chromatography. Hemagglutinating activity, with a very low titer suggesting the presence of lectin appeared in the supernatant from the homogenization of body with Tris-buffered saline. However, dialyzed supernatant from the precipitate homogenized by galactose in the buffer revealed strong hemagglutinating activity against human erythrocytes. The crude supernatant was applied onto lactosyl–agarose column, and only the supernatant eluted from precipitate with galactose was obtained a galactose-binding lectin with 32 kDa polypeptide was obtained from the supernatant of the precipitate, extracted in presence of galactose. It suggests that the lectin tightly binds with glycoconjugate as endogenous ligand(s) in the tissue. Hemagglutinating activity against trypsinized and glutaraldehyde-fixed human erythrocytes was specifically inhibited by D-galactose, N-acetyl-D-galactosamine, lactose, melibiose, and asialofetuin. Glycan-binding profile of the lectin analyzed by frontal affinity chromatography shows that the lectin recognizes branched complex type N-linked oligosaccharides and both type 1 (Galβ1-3GlcNAc) and type 2 (Galβ1-4GlcNAc) lactosamine. The surface plasmon resonance study of the lectin against asialofetuin showed the kass and kdiss values are 5.14 × 104 M 1 s 1 and 2.9 × 10−3 s 1, respectively. The partial primary structure of the lectin reveals 182 amino acids with novel sequence.  相似文献   

6.
A comparative study of different derivatization procedures has been performed in order to improve the stability of the reaction products o-phthalaldehyde–N-acetylcysteine (OPA–NAC) polyamines. Procedures such as solution derivatization, solution derivatization followed by retention on a packing support, derivatization on different packing supports and on-column derivatization, have been optimized and compared. The degradation rate constant (k) of the derivative was dependent on the procedure used and on the analyte. For the spermine (the most unstable isoindol tested) k was 8±2×10−2 min−1 in solution versus 7.7±1.1×10−4 min−1 on the (C18) solid support. The results obtained showed that forming the derivative on the packing support (C18) gave the best results following this procedure: conditioning the cartridges with borate buffer (1 ml, 0.5 M, pH 8), retention of the analyte, addition of 0.8 ml of OPA–NAC reagent, 0.2 ml borate buffer 0.8 M (pH 8) and elution of the isoindol with 3 ml of MeOH–borate buffer (9:1). The different derivatization procedures have been used to study the stability of the reaction products OPA–NAC polyamines formed in urine matrix using spermine as model compound. Similar results were obtained for standard solutions and urine samples.  相似文献   

7.
These studies defined the expression patterns of genes involved in fatty acid transport, activation and trafficking using quantitative PCR (qPCR) and established the kinetic constants of fatty acid transport in an effort to define whether vectorial acylation represents a common mechanism in different cell types (3T3-L1 fibroblasts and adipocytes, Caco-2 and HepG2 cells and three endothelial cell lines (b-END3, HAEC, and HMEC)). As expected, fatty acid transport protein (FATP)1 and long-chain acyl CoA synthetase (Acsl)1 were the predominant isoforms expressed in adipocytes consistent with their roles in the transport and activation of exogenous fatty acids destined for storage in the form of triglycerides. In cells involved in fatty acid processing including Caco-2 (intestinal-like) and HepG2 (liver-like), FATP2 was the predominant isoform. The patterns of Acsl expression were distinct between these two cell types with Acsl3 and Acsl5 being predominant in Caco-2 cells and Acsl4 in HepG2 cells. In the endothelial lines, FATP1 and FATP4 were the most highly expressed isoforms; the expression patterns for the different Acsl isoforms were highly variable between the different endothelial cell lines. The transport of the fluorescent long-chain fatty acid C1-BODIPY-C12 in 3T3-L1 fibroblasts and 3T3-L1 adipocytes followed typical Michaelis–Menten kinetics; the apparent efficiency (kcat/KT) of this process increases over 2-fold (2.1 × 106–4.5 × 106 s−1 M−1) upon adipocyte differentiation. The Vmax values for fatty acid transport in Caco-2 and HepG2 cells were essentially the same, yet the efficiency was 55% higher in Caco-2 cells (2.3 × 106 s−1 M−1 versus 1.5 × 106 s−1 M−1). The kinetic parameters for fatty acid transport in three endothelial cell types demonstrated they were the least efficient cell types for this process giving Vmax values that were nearly 4-fold lower than those defined form 3T3-L1 adipocytes, Caco-2 cells and HepG2 cells. The same cells had reduced efficiency for fatty acid transport (ranging from 0.82 × 106 s−1 M−1 to 1.35 × 106 s−1 M−1).  相似文献   

8.
UDP–3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) is one of the key enzymes of bacterial lipid A biosynthesis, catalyzing the removal of the N-acetyl group of UDP–3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine. The lpxC gene is essential in Gram-negative bacteria but absent from mammalian genomes, making it an attractive target for antibacterial drug discovery. Current assay methods for LpxC are not suitable for high throughput screening, since they require multiple product separation steps and the use of radioactively labeled material that is difficult to prepare. A homogenous fluorescence-based assay was developed that uses UDP–3-O-(N-hexyl-propionamide)-N-acetylglucosamine as a surrogate substrate. This surrogate can be prepared from commercially available UDP–GlcNAc by enzymatic conversion to UDP–MurNAc, which is then chemically coupled to n-hexylamine. Following the LpxC reaction, the free amine of the deacetylation product can be derivatized by fluorescamine, thus generating a fluorescent signal. This surrogate substrate has a Km of 367 μM and kcat of 0.36 s−1, compared to 2 μM and 1.5 s−1 for the natural substrate. Since no separation is needed, the assay is easily adaptable to high throughput screening. IC50s of LpxC inhibitors determined using this assay method is similar to those measured by traditional method with the natural substrate.  相似文献   

9.
Δ2-Thiazoline-2-carboxylate, the product of the suspected physiological reaction catalyzed by -amino acid oxidase, is stable to hydrolysis at 37°C and pH 7 or above, but it hydrolyzes readily at pH 5 or below to give a mixture of N- and S-oxalylcysteamines; the N-oxalyl derivative predominates at pH's above 1 while the S-oxyalyl compound is the major product at high acidities. The pH-rate profile looks like the superposition of two bell-shaped curves. The initial increase in the rate as the pH is lowered is controlled by a pKa of 3.95 and from pH 1 to 3 the rate is relatively constant (k = 6.7 × 10−4s−1 at 37°C and ionic strength 0.5 ). Below pH 1 the rate increases again to a maximum in 1 HCl and then decreases in more highly acidic solutions. The rate of conversion of S-oxalylcysteamine to N-oxalylcysteamine is inversely proportional to the hydrogen ion concentration from pH 3 to 5 but becomes largely independent of pH from pH 1 to 2. In the pH-independent region the rate is comparable with that observed by others for S-acetylcysteamine but in the pH-dependent region the rate is 20 to 25 times faster for the oxalyl derivative than for the acetyl compound. At pH 1, N-oxalylcysteamine is partially converted to the S-oxalyl derivative but the rate of hydrolysis (k = 1.0 × 10−5s−1 at 37°C) to cysteamine and oxalate of this partially equilibrated system occurs at a comparable rate. The results of this investigation are rationalized in terms of what is known about other thiazoline hydrolyses and intramolecular S to N acyl migrations. The main differences in the present case are presumably due to the fact that thiazoline-2-carboxylate can undergo hydrolysis by two reaction manifolds, one with the carboxyl unprotonated and the other with it protonated. The relevance of these results to possible reactions of thiazoline-2-carboxylate in vivo is briefly considered.  相似文献   

10.
Sympathetic nerve stimulation of the perfused mesenteric arterial bed of the rabbit, , increase the secretion of prostaglandin (PG)I2 and PGE2. Prazosin (4.8 × 10−6), and α1 adrenergic receptor antagonist, inhibited this inrease in release of PGI2 but not of PGE2 whereas rauwolsin (10−7 M), an α2 adrenergic receptor antagonist, inhibited the increase in release of PGE2 but not of PGI2. Prazosin (10−6 M) completely blocked the vasoconstrictor response to nerve stimulation, and to norepinephrine and phenylephrine administration, suggesting there to be little of an α2 adrenergic receptor component in this response. It is concluded that the increase in PGI2 release follows the activation of α1 adrenergic receptors and is therefore post-junctional in origin, whereas the increase in PGE2 release follows the activation of α2 adrenergic receptors and may be pre- and/or post-junctional in origin.Indomethacin (2.8 × 10−7, 5.6 × 10−7 and 1.12 × 10−6 M did not affect the vasoconstrictor responses to nerve stimulation at 10 Hz, whereas rauwolsin (10−7 M) in the presence of indomethacin substantially increased them. These results indicate that PGE2 does not regulate norepinephrine release following nerve stimulation at 10 Hz to rabbit mesenteric arteries, and that the inhibition of norepinephrine release following stimulation of α2 pre-junctional receptors is independent of PG involvement.  相似文献   

11.
The kinetics of substitution reactions of [η-CpFe(CO)3]PF6 with PPh3 in the presence of R-PyOs have been studied. For all the R-PyOs (R = 4-OMe, 4-Me, 3,4-(CH)4, 4-Ph, 3-Me, 2,3-(CH)4, 2,6-Me2, 2-Me), the reactions yeild the same product [η5-CpFe(CO)2PPh3]PF6, according to a second-order rate law that is first order in concentrations of [η5-CpFe(CO)3]PF6 and of R-PyO but zero order in PPh3 concentration. These results, along with the dependence of the reaction rate on the nature of R-PyO, are consistent with an associative mechanism. Activation parameters further support the bimmolecular nature of the reactions: ΔH = 13.4 ± 0.4 kcal mol−1, ΔS = −19.1 ± 1.3 cal k−1 mol−1 for 4-PhPyO; ΔH = 12.3 ± 0.3 kcal mol−1, ΔS = 24.7 ±1.0 cal K−1 mol−1 for 2-MePyO. For the various substituted pyridine N-oxides studied in this paper, the rates of reaction increase with the increasing electron-donating abilities of the substituents on the pyridine ring or N-oxide basicities, but decrease with increasing 17O chemical shifts of the N-oxides. Electronic and steric factors contributing to the reactivity of pyridine N-oxides have been quantitatively assessed.  相似文献   

12.
In this study, the hydraulic conductivity (Lp), Me2SO permeability ( Me2SO), and the reflection coefficients (ς) and their activation energies were determined for Metaphase II (MII) mouse oocytes by exposing them to 1.5 M Me2SO at temperatures of 30, 20, 10, 3, 0, and −3°C. These data were then used to calculate the intracellular concentration of Me2SO at given temperatures. Individual oocytes were immobilized using a holding pipette in 5 μl of an isosmotic PBS solution and perfused with precooled or prewarmed 1.5 M Me2SO solutions. Oocyte images were video recorded. The cell volume changes were calculated from the measurement of the diameter of the oocytes, assuming a spherical shape. The initial volume of the oocytes in the isoosmotic solution was considered 100%, and relative changes in the volume of the oocytes after exposure to the Me2SO were plotted against time. Mean (means ± SEM) Lpvalues in the presence of Me2SO ( Me2SOp) at 30, 20, 10, 3, 0, and −3°C were determined to be 1.07 ± 0.03, 0.40 ± 0.02, 0.18 ± 0.01, 7.60 × 10−2± 0.60 × 10−2, 5.29 × 10−2± 0.40 × 10−2, and 3.69 × 10−2± 0.30 × 10−2μm/min/atm, respectively. The Me2SOvalues were 3.69 × 10−3± 0.3 × 10−3, 1.07 × 10−3± 0.1 × 10−3, 2.75 × 10−4± 0.15 × 10−4, 7.83 × 10−5± 0.50 × 10−5, 5.24 × 10−5± 0.50 × 10−5, and 3.69 × 10−5± 0.40 × 10−5cm/min, respectively. The ς values were 0.70 ± 0.03, 0.77 ± 0.04, 0.81 ± 0.06, 0.91 ± 0.05, 0.97 ± 0.03, and 1 ± 0.04, respectively. The estimated activation energies (Ea) for Me2SOp, Me2SO, and ς were 16.39, 23.24, and −1.75 Kcal/mol, respectively. These data may provide the fundamental basis for the development of more optimal cryopreservation protocols for MII mouse oocytes.  相似文献   

13.
Prostaglandin I2 potentiated the paw swelling induced by carrageenin in rats. Prostaglandin I2 (0.1 μg) showed similar activity to PGE1 (0.01 μg). This potentiating property disappeared in 60 minutes and was completely abolished by diphenhydramine (25 mg kg−1, i.p.). In vascular permeability tests, PGI2 itself (2.5 × 10−10 mol, 88 ng) caused no dye leakage reaction, but PGE1 (2.5 × 10−10 mol, 88.5 ng) caused a significant dye leakage. This effect of PGE1 was statistically significant compared with vehicle- or PGI2-treated group (p<0.05). Prostaglandin I2 potentiated the increased vascular permeability induced by 5-hydroxytriptamine (2.5 × 10−10 mol), bradykinin (5 × 10−10 mol) and histamine (2 × 10−10 to 2 × 10−8 mol). The potentiation was the most evidence in the case of histamine.  相似文献   

14.
The nitrogen uptake and growth capabilities of the potentially harmful, raphidophycean flagellate Heterosigma akashiwo (Hada) Sournia were examined in unialgal batch cultures (strain CCMP 1912). Growth rates as a function of three nitrogen substrates (ammonium, nitrate and urea) were determined at saturating and sub-saturating photosynthetic photon flux densities (PPFDs). At saturating PPFD (110 μE m−2 s−1), the growth rate of H. akashiwo was slightly greater for cells grown on NH4+ (0.89 d−1) compared to cells grown on NO3 or urea, which had identical growth rates (0.82 d−1). At sub-saturating PPFD (40 μE m−2 s−1), both urea- and NH4+-grown cells grew faster than NO3-grown cells (0.61, 0.57 and 0.46 d−1, respectively). The N uptake kinetic parameters were investigated using exponentially growing batch cultures of H. akashiwo and the 15N-tracer technique. Maximum specific uptake rates (Vmax) for unialgal cultures grown at 15 °C and saturating PPFD (110 μE m−2 s−1) were 28.0, 18.0 and 2.89 × 10−3 h−1 for NH4+, NO3 and urea, respectively. The traditional measure of nutrient affinity—the half saturation constants (Ks) were similar for NH4+ and NO3 (1.44 and 1.47 μg-at N L−1), but substantially lower for urea (0.42 μg-at N L−1). Whereas the α parameter (α = Vmax/Ks), which is considered a more robust indicator for substrate affinity when substrate concentrations are low (<Ks), were 19.4, 12.2 and 6.88 × 10−3 h−1/(μg-at N L−1) for NH4+, NO3 and urea, respectively. These laboratory results demonstrate that at both saturating and sub-saturating N concentrations, N uptake preference follows the order: NH4+ > NO3 > urea, and suggests that natural blooms of H. akashiwo may be initiated or maintained by any of the three nitrogen substrates examined.  相似文献   

15.
An unreported graft copolymer of N,N-dimethylacrylamide (DMA) with chitosan has been synthesized under nitrogen atmosphere using peroxymonosulphate/mandelic acid redox pair. The effect of reaction conditions on grafting parameters i.e. grafting ratio, efficiency, conversion, add on and homopolymer has been studied. Experimental results show that maximum grafting has been obtained at 1.0 g dm−3 concentration of chitosan, 30 × 10−2 mol dm−3 concentration of N,N-dimethylacrylamide and 7.0 × 10−3 mol dm−3 concentration of hydrogen ion. It has also been observed that grafting ratio, add on, conversion and efficiency increase upto 3.2 × 10−3 mol dm−3 of mandelic acid, 12.0 × 10−3 mol dm−3 of potassium peroxymonosulphate, 150 min of time and 40 °C of temperature. Grafted polymer has been characterized by FTIR spectroscopy and thermogravimetric analysis. Water swelling capacity of chitosan-g-N,N-dimethylacrylamide has been determined. It has been observed that the graft copolymer is thermally more stable than parent backbone.  相似文献   

16.
Since there is evidence that oxalyl thiolesters (RSCOCOO) are present in animal cells, and possibly may participate in the control of metabolism, the present study was undertaken to characterize their reactivity with nucleophiles so that one could gain a better understanding of how they might be affecting the activities of enzymes. At 25°C and neutral pH, N-acetyl-S-oxalyl-2-aminoethanethiol (NAC-S-Ox) reacts rapidly with cysteamine (2-aminoethanethiol) to give N-acetylcysteamine and N-oxalylcysteamine. Under similar conditions, other aminothiols, such as cysteine, homocysteine, penicillamine, and cysteine ethyl ester, also react rapidly with NAC-S-Ox, but non-thiol-containing amines, such as alanine, alanine ethyl ester, glycine, and S-methylcysteine, react more than four orders of magnitude less rapidly. The aminothiol reactions apparently proceed by rate-determining oxalyl transfer to the thiol followed by a rapid intramolecular S- to N-oxalyl migration. The reactions follow second-order kinetics with the thiolate anion being the reactive nucleophile. At 25°C and ionic strength 1.0 , kN, defined in the equation, rate = kN[RS][NAC-S-Ox], has the following values ( −1 s−1) for the anion of the reacting thiol: cysteamine, 170; cysteine, 260; cysteine ethyl ester, 76; homocysteine, 380. Rate data for the reaction of NAC-S-Ox with hydroxylamine, imidazole, hydroperoxide, and hydroxide were also obtained. The reaction of S-oxalyl-p-thiocresol with thiol anions under the same conditions gives the following values for kN ( −1 s−1 × 10−3): glutathione, 5.6; N-acetylcysteamine, 3.7; pantetheine, 4.8; 8-mercaptooctanoic acid, 4.5; 6-mercaptooctanoic acid, 1.0; dihydrolipoic acid, 8.2. These results indicate that oxalyl transfers from oxalyl thiolesters to thiol anions occur more than two orders of magnitude more rapidly than corresponding acetyl transfers, and that under physiological conditions any in vivo oxalyl thiolester would equilibrate within minutes with virtually every thiol in the cell, including those attached to enzymes. Consequently, it is proposed that one mechanism by which oxalyl thiolesters may function in vivo to alter the catalytic activities of enzymes is to covalently modify enzymic thiols by acylation with an oxalyl group.  相似文献   

17.
The rate constant for the hydrolysis of prostacyclin (PGI2) to 6-keto-PGF was measured by monitoring the UV spectral change, over a pH range 6 to 10 at 25°C and the total ionic strength of 0.5 M. The first-order rate constant (kobs) extrapolated to zero buffer concentration follows an expression, kobs = kH+ (H+), where kH+ is a second-order rate constant for the specific acid catalyzed hydrolysis. The value of kH+ obtained (3.71 × 104 sec−1 M−1) is estimated approximately 700-fold greater than a kH+ value expected from the hydrolysis of other vinyl ethers. Such an unusually high reactivity of PGI2 even for a vinyl ether is attributed to a possible ring strain release that would occur upon the rate controlling protonation of C5. A Brønsted slope (α) of 0.71 was obtained for the acid (including H3O+) catalytic constants, from which a pH independent first-order rate constant for the spontaneous hydrolysis (catalyzed by H2O as a general acid) was estimated to be 1.3 × 10−6 sec−1. An apparent activation energy (Ea) of 11.85 Kcal/mole was obtained for the hydrolysis at pH 7.48, from which a half-life of PGI2 at 4°C was estimated to be approximately 14.5 min. when the total phosphate concentration is 0.165 M (cf. 3.5 min. at 25°C).  相似文献   

18.
A series of electrophilic glutamine analogues based on 6-diazo-5-oxo-norleucine has been prepared, using novel synthetic routes, and evaluated as inhibitors of Escherichia coli. glucosamine synthetase. The γ-dimethylsulphonium salt analogue of glutamine was found to be one of the most potent inactivators of this enzyme yet reported, with an apparent second order rate constant (k2/Ki) of 3.5×105 M−1 min−1.  相似文献   

19.
We measured nitrous oxide (N2O), dinitrogen (N2), methane (CH4), and carbon dioxide (CO2) fluxes in horizontal and vertical flow constructed wetlands (CW) and in a riparian alder stand in southern Estonia using the closed chamber method in the period from October 2001 to November 2003. The replicates’ average values of N2O, N2, CH4 and CO2 fluxes from the riparian gray alder stand varied from −0.4 to 58 μg N2O-N m−2 h−1, 0.02–17.4 mg N2-N m−2 h−1, 0.1–265 μg CH4-C m−2 h−1 and 55–61 mg CO2-C m−2 h−1, respectively. In horizontal subsurface flow (HSSF) beds of CWs, the average N2 emission varied from 0.17 to 130 and from 0.33 to 119 mg N2-N m−2 h−1 in the vertical subsurface flow (VSSF) beds. The average N2O-N emission from the microsites above the inflow pipes of the HSSF CWs was 6.4–31 μg N2O-N m−2 h−1, whereas the outflow microsites emitted 2.4–8 μg N2O-N m−2 h−1. In VSSF beds, the same value was 35.6–44.7 μg N2O-N m−2 h−1. The average CH4 emission from the inflow and outflow microsites in the HSSF CWs differed significantly, ranging from 640 to 9715 and from 30 to 770 μg CH4-C m−2 h−1, respectively. The average CO2 emission was somewhat higher in VSSF beds (140–291 mg CO2-C m−2 h−1) and at the inflow microsites of HSSF beds (61–140 mg CO2-C m−2 h−1). The global warming potential (GWP) from N2O and CH4 was comparatively high in both types of CWs (4.8 ± 9.8 and 6.8 ± 16.2 t CO2 eq ha−1 a−1 in the HSSF CW 6.5 ± 13.0 and 5.3 ± 24.7 t CO2 eq ha−1 a−1 in the hybrid CW, respectively). The GWP of the riparian alder forest from both N2O and CH4 was relatively low (0.4 ± 1.0 and 0.1 ± 0.30 t CO2 eq ha−1 a−1, respectively), whereas the CO2-C flux was remarkable (3.5 ± 3.7 t ha−1 a−1). The global influence of CWs is not significant. Even if all global domestic wastewater were treated by wetlands, their share of the trace gas emission budget would be less than 1%.  相似文献   

20.
The effects of prostaglandin F (PGF) on propulsive activity in segments of isolated colon and on isolated strips of guinea-pig colon were investigated.Using experimental conditions under which spontaneous propulsive activity was negligible, PGF (5×10−8×1×10−6M), added to the bathing medium, increased propulsive activity in a concentration dependent manner. This increase of propulsive activity was abolished in the presence of atropine or tetrodotoxin (1×10−7g/ml).The contractions produced by PGF(5×10−7 − 1×10−5M) in isolated longitudinal and circular smooth muscle strips of guinea-pig colon were unaffected in the presence of atropine or tetrodotoxin (1×10−7 g/ml).From these results it is concluded that under the conditions employed in this study propulsive activity stimulated by PGF may depend on the contractions of both muscle layers and stimulation of the peristalic reflex.  相似文献   

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