共查询到20条相似文献,搜索用时 750 毫秒
1.
The electric quadrupole moment of the deuterium nucleus provides a nuclear magnetic resonance (NMR) probe of electric field gradients, and thereby of organization of tissue water. 8-17% of H 2O in rat muscle and brain was replaced by D 2O from 50% deuterated drinking water. The peak height of the steady-state NMR spectrum of D in muscle water was 74% lower than that of an equal concentration of D 2O in liquid water. Longitudinal NMR relaxation times ( T1) of D in water of muscle and brain averaged 0.092 and 0.131 sec, respectively, compared with 0.47 sec in D 2O in liquid water. Transverse NMR relaxation times ( T2) averaged 0.009 and 0.022 sec in D 2O of muscle and brain, respectively, compared with 0.45 sec in D 2O in liquid water. These differences cannot be explained by paramagnetic ions or by magnetic inhomogeneities, which leaves increased organization of tissue water as the only tenable hypothesis. Evidence was also obtained that 27% of muscle water and 13% of brain water exist as a separate fraction with T2 of D 2O less than 2 × 10 -3 sec, which implies an even higher degree of structure. Each of the two fractions may consist of multiple subfractions of differing structure. 相似文献
2.
Changes in water content and dry weight were determined in control cells and those induced to cold harden in response to abscisic acid (ABA) treatment (7.5 × 10 −5 molar). Bromegrass ( Bromus inermis Leyss cv Manchar) cells grown in suspension culture at room temperature (23°C) for 7 days acclimated to −28°C (LT 50) when treated with ABA, or to −5°C when untreated. ABA significantly reduced cell growth rates at 5 and 7 days after treatment. Growth reduction was due to a decrease in cell number rather than cell size. When the cell water content was expressed as percent water (percent H 2O) or as grams water per gram dry weight (gram H 2O/gram dry weight [g DW]), the water content of hardy, ABA-treated cells decreased from 85% to 77% or from 6.4 to 3.3 g H 2O/g DW in 7 days. Control cell water content remained static at approximately 87% and 7.5 g H 2O/g DW. However, cell water content, expressed as milligrams water per million cells (milligram H 2O/10 6 cells), did not differ in ABA-treated or control cells. The dry matter content of ABA-treated cells, expressed as milligram DW/10 6 cells increased to 3.3 milligram/10 6 cells in 7 days, whereas the dry weight of the control cells remained between 1.4 to 2.1 milligrams/10 6 cells. The osmotic potential of ABA-treated cells decreased by the fifth day while that of control cells increased significantly and then decreased by day 7. Elevated osmotic potentials were not associated with increased ion uptake. In contrast to much published literature, these results suggest that cell water content does not decrease in ABA-treated cells during the induction of freezing tolerance, rather the dry matter mass per cell increased. Cell water content may be more accurately expressed as a function of cell number when accompanying changes to dry cell matter occur. 相似文献
3.
ObjectiveNa + can be stored in muscle and skin without commensurate water accumulation. The aim of this study was to assess Na + and H 2O in muscle and skin with MRI in acute heart failure patients before and after diuretic treatment and in a healthy cohort. MethodsNine patients (mean age 78 years; range 58–87) and nine age and gender-matched controls were studied. They underwent 23Na/ 1H-MRI at the calf with a custom-made knee coil. Patients were studied before and after diuretic therapy. 23Na-MRI gray-scale measurements of Na +-phantoms served to quantify Na +-concentrations. A fat-suppressed inversion recovery sequence was used to quantify H 2O content. ResultsPlasma Na +-levels did not change during therapy. Mean Na +-concentrations in muscle and skin decreased after furosemide therapy (before therapy: 30.7±6.4 and 43.5±14.5 mmol/L; after therapy: 24.2±6.1 and 32.2±12.0 mmol/L; p˂0.05 and p˂0.01). Water content measurements did not differ significantly before and after furosemide therapy in muscle ( p = 0.17) and only tended to be reduced in skin ( p = 0.06). Na +-concentrations in calf muscle and skin of patients before and after diuretic therapy were significantly higher than in healthy subjects (18.3±2.5 and 21.1±2.3 mmol/L). Conclusions
23Na-MRI shows accumulation of Na + in muscle and skin in patients with acute heart failure. Diuretic treatment can mobilize this Na +-deposition; however, contrary to expectations, water and Na +-mobilization are poorly correlated. 相似文献
4.
Surface water and groundwater are continuously used as sources of drinking water in many metropolitan areas of the United States. The quality of water from these sources may be reduced due to increases in contaminants such as Escherichia coli from urban and agricultural runoffs. In this study, a multiplex fluorogenic PCR assay was used to quantify E. coli O157:H7 in soil, manure, cow and calf feces, and dairy wastewater in an artificial wetland. Primers and probes were designed to amplify and quantify the Shiga-like toxin 1 ( stx1) and 2 ( stx2) genes and the intimin ( eae) gene of E. coli O157:H7 in a single reaction. Primer specificity was confirmed with DNA from 33 E. coli O157:H7 and related strains with and without the three genes. A direct correlation was determined between the fluorescence threshold cycle ( CT) and the starting quantity of E. coli O157:H7 DNA. A similar correlation was observed between the CT and number of CFU per milliliter used in the PCR assay. A detection limit of 7.9 × 10 −5 pg of E. coli O157:H7 DNA ml −1 equivalent to approximately 6.4 × 10 3 CFU of E. coli O157:H7 ml −1 based on plate counts was determined. Quantification of E. coli O157:H7 in soil, manure, feces, and wastewater was possible when cell numbers were ≥3.5 × 10 4 CFU g −1. E. coli O157:H7 levels detected in wetland samples decreased by about 2 logs between wetland influents and effluents. The detection limit of the assay in soil was improved to less than 10 CFU g −1 with a 16-h enrichment. These results indicate that the developed PCR assay is suitable for quantitative determination of E. coli O157:H7 in environmental samples and represents a considerable advancement in pathogen quantification in different ecosystems. 相似文献
5.
The sensitivity of a test for cattle shedding Escherichia coli serogroup O26 was estimated using several fecal pats artificially inoculated at a range of concentrations with different E. coli O26 strains. The test involves the enrichment of fecal microflora in buffered peptone water, the selective concentration of E. coli O26 using antibody-coated immunomagnetic-separation beads, the identification of E. coli colonies on Chromocult tryptone bile X-glucuronide agar, and confirmation of the serogroup with E. coli serogroup O26-specific antisera using slide agglutination. The effective dose of E. coli O26 for an 80% test sensitivity (ED 80) was 1.0 × 10 4 CFU g −1 feces (95% confidence interval, 4.7 × 10 3 to 2.4 × 10 4). Differences in test sensitivity between different E. coli O26 strains and fecal pats were also observed. Individual estimates of ED 80 for each strain and fecal pat combination ranged from 4.2 × 10 2 to 4.8 × 10 5 CFU g −1. These results suggest that the test is useful for identifying individuals shedding a large number of E. coli O26 organisms or, if an appropriate number of individuals in a herd are sampled, for identifying affected herds. The study also provides a benchmark estimate of sensitivity that can be used to compare alternative tests for E. coli O26 and a methodological approach that can be applied to tests for other pathogenic members of the Enterobacteriaceae and other sample types. 相似文献
6.
The comparison of volumes of cells and subcellular structures with the pH values reported for them leads to a conflict with the definition of the pH scale. The pH scale is based on the ionic product of water, K
w = [H +]×[OH −].We used K
w [in a reversed way] to calculate the number of undissociated H 2O molecules required by this equilibrium constant to yield at least one of its daughter ions, H + or OH − at a given pH. In this way we obtained a formula that relates pH to the minimal volume V pH required to provide a physical meaning to K
w, (where N
A is Avogadro’s number). For example, at pH 7 (neutral at 25°C) V pH = 16.6 aL. Any deviation from neutral pH results in a larger V pH value. Our results indicate that many subcellular structures, including coated vesicles and lysosomes, are too small to contain free H + ions at equilibrium, thus the definition of pH based on K
w is no longer valid. Larger subcellular structures, such as mitochondria, apparently contain only a few free H + ions. These results indicate that pH fails to describe intracellular conditions, and that water appears to be dissociated too weakly to provide free H + ions as a general source for biochemical reactions. Consequences of this finding are discussed. 相似文献
7.
Neutron reflectivities of phosphatidylcholine monolayers in the liquid condensed (LC) phase on ultrapure H 2O and D 2O subphases have been measured on a Langmuir film balance. Using a dedicated liquid surface reflectometer, reflectivities down to R = 10 -6 in the momentum transfer range Qz = 0-0.4 Å -1 were accessed. In a new approach, by refining neutron reflectivity data from chain-perdeuterated DPPC-d62 in combination with x-ray measurements on the same monolayer under similar conditions it is shown that the two techniques mutually complement one another. This analysis leads to a detailed conception of the interface structure. It is found that in the LC phase (which is analogous to the Lβ, phase in vesicle dispersions) the head group is interpenetrated with subphase water (4 ± 2.5 molecules per lipid) and the average tilt angle of the hydrophobic chains from the surface normal is 33 ± 3 degrees. 相似文献
8.
Background/AimsResveratrol has been demonstrated to be protective in the cardiovascular system. The aim of this study was to assess the effects of resveratrol on hydrogen peroxide (H 2O 2)-induced increase in late sodium current ( I
Na.L) which augmented the reverse Na +-Ca 2+ exchanger current ( I
NCX), and the diastolic intracellular Ca 2+ concentration in ventricular myocytes. Methods
I
Na.L, I
NCX, L-type Ca 2+ current ( I
Ca.L) and intracellular Ca 2+ properties were determined using whole-cell patch-clamp techniques and dual-excitation fluorescence photomultiplier system (IonOptix), respectively, in rabbit ventricular myocytes. ResultsResveratrol (10, 20, 40 and 80 µM) decreased I
Na.L in myocytes both in the absence and presence of H 2O 2 (300 µM) in a concentration dependent manner. Ranolazine (3–9 µM) and tetrodotoxin (TTX, 4 µM), I
Na.L inhibitors, decreased I
Na.L in cardiomyocytes in the presence of 300 µM H 2O 2. H 2O 2 (300 µM) increased the reverse I
NCX and this increase was significantly attenuated by either 20 µM resveratrol or 4 µM ranolazine or 4 µM TTX. In addition, 10 µM resveratrol and 2 µM TTX significantly depressed the increase by 150 µM H 2O 2 of the diastolic intracellular Ca 2+ fura-2 fluorescence intensity (FFI), fura-fluorescence intensity change (△FFI), maximal velocity of intracellular Ca 2+ transient rise and decay. As expected, 2 µM TTX had no effect on I
Ca.L. ConclusionResveratrol protects the cardiomyocytes by inhibiting the H 2O 2-induced augmentation of I
Na.L.and may contribute to the reduction of ischemia-induced lethal arrhythmias. 相似文献
9.
A β-class carbonic anhydrase (CA, EC 4.2.1.1) was cloned from the genome of the Monogenean platyhelminth Gyrodactylus salaris, a parasite of Atlantic salmon. The new enzyme, GsaCAβ has a significant catalytic activity for the physiological reaction, CO 2 + H 2O ⇋ HCO 3− + H + with a k cat of 1.1 × 10 5 s −1 and a k cat/K m of 7.58 × 10 6 M −1 × s −1. This activity was inhibited by acetazolamide (K I of 0.46 µM), a sulphonamide in clinical use, as well as by selected inorganic anions and small molecules. Most tested anions inhibited GsaCAβ at millimolar concentrations, but sulfamide (K I of 81 µM), N,N-diethyldithiocarbamate (K I of 67 µM) and sulphamic acid (K I of 6.2 µM) showed a rather efficient inhibitory action. There are currently very few non-toxic agents effective in combating this parasite. GsaCAβ is subsequently proposed as a new drug target for which effective inhibitors can be designed. 相似文献
10.
Using Time Domain 1H Nuclear Magnetic Resonance with H 217O (H 217O-TD- 1HNMR), we found [H 217O]- and pH-controlled chiral differences in proton exchange properties in alanine (Ala) and asparagine (Asn). To minimize
and equalize chemical impurities, Asn enantiomers were purified by crystallization from racemic solution. At <0.1 M H 217O, a shift in isoelectric pH (pI) occurred, ~1.14 kJ mol −1
l- d-Asn ΔΔ G
o′ in the 5.91–6.42 pH range. One potential source for this asymmetry is the enantio-different magnetic moments ( lμ↑ ≠ dμ↓) produced by neutral ring currents in the chiral center, leading to enantio-different nuclear spin organization and charge
distribution in the amino group. At ≥pI, dissimilar interactions may occur in the hydration of the amino group with H 217O (NH 2/H 217O ≠ NH 2/H 216O; NH 3
+/H 217O ≠ NH 2/H 217O; l-*C-NH 2/H 217O ≠ d-*C-NH 2/H 217O). As lμ↑ ≠ dμ↓, the l-*C-amino and the d-*C-amino groups are diastereo spin-isomers. The nuclear spin of 17O may be parallel or antiparallel with the ortho- 1H 1H pair; hence two ortho-H 217O molecules exist, also diastereo spin-isomers. As the pK of H 217O is different from H 216O, dissimilarities between l-*C- and d-*C-amino groups are converted into proton exchange differences. During H 217O-TD- 1HNMR, the H 217O molecule is a “probe” of the state of the amino group. Regarding prebiotic evolution: prebiotic chirality may not require
stochastic symmetry breaking or preexisting chiral conditions; chemical chiral effects due to lμ↑ ≠ dμ↓ are small and need chiral amplification to generate an enantiomeric excess significant for prebiotic evolution; and prebiotic
symmetry breaking was homochiral because the effect of lμ↑ and dμ↓ on the amino group should be similar in all alpha amino acids. 相似文献
11.
Pure cultures of the marine ammonium-oxidizing bacterium Nitrosomonas sp. were grown in the laboratory at oxygen partial pressures between 0.005 and 0.2 atm (0.18 to 7 mg/liter). Low oxygen conditions induced a marked decrease in the rate for production of NO 2-, from 3.6 × 10 −10 to 0.5 × 10 −10 mmol of NO 2- per cell per day. In contrast, evolution of N 2O increased from 1 × 10 −12 to 4.3 × 10 −12 mmol of N per cell per day. The yield of N 2O relative to NO 2- increased from 0.3% to nearly 10% (moles of N in N 2O per mole of NO 2-) as the oxygen level was reduced, although bacterial growth rates changed by less than 30%. Nitrifying bacteria from the genera Nitrosomonas, Nitrosolobus, Nitrosospira, and Nitrosococcus exhibited similar yields of N 2O at atmospheric oxygen levels. Nitrite-oxidizing bacteria ( Nitrobacter sp.) and the dinoflagellate Exuviaella sp. did not produce detectable quantities of N 2O during growth. The results support the view that nitrification is an important source of N 2O in the environment. 相似文献
12.
Spraying mustard ( Sinapis alba L.) seedlings with salicylic acid (SA) solutions between 10 and 500 μm significantly improved their tolerance to a subsequent heat shock at 55°C for 1.5 h. The effects of SA were concentration dependent, with higher concentrations failing to induce thermotolerance. The time course of thermotolerance induced by 100 μm SA was similar to that obtained with seedlings acclimated at 45°C for 1 h. We examined the hypothesis that induced thermotolerance involved H 2O 2. Heat shock at 55°C caused a significant increase in endogenous H 2O 2 and reduced catalase activity. A peak in H 2O 2 content was observed within 5 min of either SA treatment or transfer to the 45°C acclimation temperature. Between 2 and 3 h after SA treatment or heat acclimation, both H 2O 2 and catalase activity significantly decreased below control levels. The lowered H 2O 2 content and catalase activity occurred in the period of maximum thermoprotection. It is suggested that thermoprotection obtained either by spraying SA or by heat acclimation may be achieved by a common signal transduction pathway involving an early increase in H 2O 2. 相似文献
13.
Aquaporins are highly selective water channel proteins integrated into plasma membranes of single cell organisms; plant roots and stromae; eye lenses, renal and red blood cells in vertebrates. To date, only a few microbial aquaporins have been characterized and their physiological importance is not well understood. Here we report on the cloning, expression and characterization of a novel aquaporin, RsAqpZ, from a purple photosynthetic bacterium, Rhodobacter sphaeroides ATCC 17023. The protein was expressed homologously at a high yield (∼20 mg/L culture) under anaerobic photoheterotrophic growth conditions. Stopped-flow light scattering experiments demonstrated its high water permeability (0.17±0.05 cm/s) and low energy of activation for water transport (2.93±0.60 kcal/mol) in reconstituted proteoliposomes at a protein to lipid ratio (w/w) of 0.04. We developed a fluorescence correlation spectroscopy based technique and utilized a fluorescent protein fusion of RsAqpZ, to estimate the single channel water permeability of RsAqpZ as 1.24 (±0.41) x 10 −12 cm 3/s or 4.17 (±1.38)×10 10 H 2O molecules/s, which is among the highest single channel permeability reported for aquaporins. Towards application to water purification technologies, we also demonstrated functional incorporation of RsAqpZ in amphiphilic block copolymer membranes. 相似文献
14.
Two new zinc complexes, Zn(HL 1) 2 (1) and [Zn 2(H 2L 2)(OAc) 2] 2 (2) [H 2L 1 = Schiff base derived from o-vanillin and ( R)-(+)-2-amino-3-phenyl-1-propanol, H 3L 2 = Schiff base derived from o-vanillin and 2-amino-2-ethyl-1,3-propanediol], have been synthesized and characterized by single crystal X-ray diffraction, elemental analyses, TG analyses, solid fluorescence, IR, UV-Vis and circular dichroism spectra. The structural analysis shows that complex 1 has a right-handed double helical chain along the crystallographic b axis. A homochiral 3D supramolecular architecture has been further constructed by intermolecular C-H··· π, O-H···O and C-H···O interactions. Complex 2 includes two crystallographically independent binuclear zinc molecules. The two binuclear zinc molecules are isostructural. The 2-D sheet supramolecular structure was formed by intermolecular hydrogen bonding interaction. The fluorescence of ligands and complexes in DMF at room temperature are studied. The interactions of two complexes with calf thymus DNA (CT-DNA) are investigated using UV-Vis, CD and fluorescence spectroscopy. The results show that complex 1 exhibits higher interaction with CT-DNA than complex 2. In addition, in vitro cytotoxicity of the complexes towards four kinds of cancerous cell lines (A549, HeLa, HL-60 and K562) were assayed by the MTT method. Investigations on the structures indicated that the chirality and nuclearity of zinc complexes play an important role on cytotoxic activity. 相似文献
15.
The hydraulic conductivity of the membranes surrounding the giant axon of the squid, Dosidicus gigas, was measured. In some axons the axoplasm was partially removed by suction. Perfusion was then established by insertion of a second pipette. In other axons the axoplasm was left intact and only one pipette was inserted. In both groups hydrostatic pressure was applied by means of a water column in a capillary manometer. Displacement of the meniscus in time gave the rate of fluid flowing across the axon sheath. In both groups osmotic differences across the membrane were established by the addition of a test molecule to the external medium which was seawater. The hydraulic conductivity determined by application of hydrostatic pressure was 10.6 ± 0.8.10 -8 cm/sec cm H 2O in perfused axons and 3.2 ± 0.6.10 -8 cm/sec cm H 2O in intact axons. When the driving force was an osmotic pressure gradient the conductivity was 4.5 ± 0.6 x 10 -10 cm/sec cm H 2O and 4.8 ± 0.9 x 10 -10 cm/sec cm H 2O in perfused and intact axons, respectively. A comparable result was found when the internal solution was made hyperosmotic. The fluid flow was a linear function of the hydrostatic pressure up to 70 cm of water. Glycerol outflux and membrane conductance were increased 1.6 and 1.1 times by the application of hydrostatic pressure. These increments do not give an explanation of the difference between the filtration coefficients. Other possible explanations are suggested and discussed. 相似文献
16.
Careful experiments on the measurement of the intensity of the deuterium NMR signal for 2H 2O in muscle and in its distillate were performed, and they showed that all 2H 2O in muscles is “NMR visible.”The spin-lattice relaxation time ( T1) of the water protons in the muscle and liver of mice and in egg white has been studied at six frequencies ranging from 4.5 to 6.0 MHz over the temperature range of +37 to −70°C. T1 values of deuterons in 2H 2O of gastrocnemius muscle and liver of mice have been measured at three frequencies (4.5, 9.21 and 15.35 MHz) over the temperature range of +37 to −20°C. Calculations on T1 for both proton and deuteron have been made and compared with the experimental data. It is suggested that the reduction of the T1 values compared to pure water and the frequency dependence of T1 are due to water molecules in the hydration layer of the macromolecules, and that the bulk of water molecules in the biological tissues and egg white undergoes relaxation like ordinary liquid water. 相似文献
17.
Primary tropical forests generally exhibit large gaseous nitrogen (N) losses, occurring as nitric oxide (NO), nitrous oxide (N 2O) or elemental nitrogen (N 2). The release of N 2O is of particular concern due to its high global warming potential and destruction of stratospheric ozone. Tropical forest soils are predicted to be among the largest natural sources of N 2O; however, despite being the world’s second-largest rainforest, measurements of gaseous N-losses from forest soils of the Congo Basin are scarce. In addition, long-term studies investigating N 2O fluxes from different forest ecosystem types (lowland and montane forests) are scarce. In this study we show that fluxes measured in the Congo Basin were lower than fluxes measured in the Neotropics, and in the tropical forests of Australia and South East Asia. In addition, we show that despite different climatic conditions, average annual N 2O fluxes in the Congo Basin’s lowland forests (0.97 ± 0.53 kg N ha −1 year −1) were comparable to those in its montane forest (0.88 ± 0.97 kg N ha −1 year −1). Measurements of soil pore air N 2O isotope data at multiple depths suggests that a microbial reduction of N 2O to N 2 within the soil may account for the observed low surface N 2O fluxes and low soil pore N 2O concentrations. The potential for microbial reduction is corroborated by a significant abundance and expression of the gene nosZ in soil samples from both study sites. Although isotopic and functional gene analyses indicate an enzymatic potential for complete denitrification, combined gaseous N-losses (N 2O, N 2) are unlikely to account for the missing N-sink in these forests. Other N-losses such as NO, N 2 via Feammox or hydrological particulate organic nitrogen export could play an important role in soils of the Congo Basin and should be the focus of future research.Subject terms: Microbiology, Biogeochemistry 相似文献
18.
The dormant cysts of Artemia undergo cycles of hydration-dehydration without losing viability. Therefore, Artemia cysts serve as an excellent intact cellular system for studying the dynamics of water-protein interactions as a function of hydration. Deuterium spin-lattice ( T1) and spin-spin ( T2) relaxation times of water in cysts hydrated with D 2O have been measured for hydrations between 1.5 and 0.1 g of D 2O per gram of dry solids. When the relaxation rates (I/ T1, I/ T2) of 2H and 17O are plotted as a function of the reciprocal of hydration (1/H), an abrupt change in slope is observed near 0.6 g of D 2O (or H 2 17O)/gram of dry solids, the hydration at which conventional metabolism is activated in this system. The results have been discussed in terms of the two-site and multisite exchange models for the water-protein interaction as well as protein dynamics models. The 2H and 17O relaxation rates as a function of hydration show striking similarities to those observed for anisotropic motion of water molecules in protein crystals. It is suggested here that although the simple two-site exchange model or n-site exchange model could be used to explain our data at high hydration levels, such models are not adequate at low hydration levels (<0.6 g H2O/g) where several complex interactions between water and proteins play a predominant role in the relaxation of water nuclei. We further suggest that the abrupt change in the slope of I/T1 as a function of hydration in the vicinity of 0.6 g H2O/g is due to a change in water-protein interactions resulting from a variation in the dynamics of protein motion. 相似文献
19.
Human cystathionine β-synthase (CBS), a novel heme-containing pyridoxal 5′-phosphate enzyme, catalyzes the condensation of homocysteine and serine or cysteine to produce cystathionine and H 2O or H 2S, respectively. The presence of heme in CBS has limited spectrophotometric characterization of reaction intermediates by masking the absorption of the pyridoxal 5′-phosphate cofactor. In this study, we employed difference stopped-flow spectroscopy to characterize reaction intermediates formed under catalytic turnover conditions. The reactions of l-serine and l-cysteine with CBS resulted in the formation of a common aminoacrylate intermediate ( kobs = 0.96 ± 0.02 and 0.38 ± 0.01 m m−1 s −1, respectively, at 24 °C) with concomitant loss of H 2O and H 2S and without detectable accumulation of the external aldimine or other intermediates. Homocysteine reacted with the aminoacrylate intermediate with kobs = 40.6 ± 3.8 s −1 and re-formed the internal aldimine. In the reverse direction, CBS reacted with cystathionine, forming the aminoacrylate intermediate with kobs = 0.38 ± 0.01 m m−1 s −1. This study provides the first insights into the pre-steady-state kinetic mechanism of human CBS and indicates that the reaction is likely to be limited by a conformational change leading to product release. 相似文献
20.
Scrapings of decomposing Cladophora sp. mats (periphyton) covering stream bed rocks produced N 2O when incubated under N 2 plus 15% C 2H 2. Denitrification (N 2O formation) was enhanced by NO 3− and was inhibited by autoclaving, Hg 2+, and O 2. No N 2O was formed in the absence of C 2H 2 (air or N 2 atmosphere). Chloramphenicol did not block N 2O formation, indicating that the enzymes were constitutive. In field experiments, incubation of periphyton scrapings in the light inhibited denitrification because of algal photosynthetic O 2 production. The diurnal periphyton-associated denitrification rate was estimated to be 45.8 μmol of N 2O·m −2·day −1, as determined by averaging light, aerobic plus dark, and anaerobic rates over a 24-h period. 相似文献
|