共查询到20条相似文献,搜索用时 15 毫秒
1.
R. Nogueira V. Lazarova J. Manem L. F. Melo 《Bioprocess and biosystems engineering》1998,19(6):441-449
The influence of dissolved oxygen concentration on the nitrification kinetics was studied in the circulating bed reactor (CBR). The study was partly performed at laboratory scale with synthetic water, and partly at pilot scale with secondary effluent as feed water. The nitrification kinetics of the laboratory CBR as a function of the oxygen concentration can be described according to the half order and zero order rate equations of the diffusion-reaction model applied to porous catalysts. When oxygen was the rate limiting substrate, the nitrification rate was close to a half order function of the oxygen concentration. The average oxygen diffusion coefficient estimated by fitting the diffusion-reaction model to the experimental results was around 66% of the respective value in water. The experimental results showed that either the ammonia or the oxygen concentration could be limiting for the nitrification kinetics. The latter occurred for an oxygen to ammonia concentration ratio below 1.5–2 gO2/gN-NH4 + for both laboratory and pilot scale reactors. The volumetric oxygen mass transfer coefficient (k L a) determined in the laboratory scale reactor was 0.017?s?1 for a superficial air velocity of 0.02?m s?1, and the one determined in the pilot scale reactor was 0.040?s?1 for a superficial air velocity of 0.031?m?s?1. The k L a for the pilot scale reactor did not change significantly after biofilm development, compared to the value measured without biofilm. 相似文献
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3.
D M Easton 《Journal of theoretical biology》1979,76(3):335-349
From the assumption that the fractional increase of HbO2 as a function of pO2 is proportional to HbO2, and that the proportionality coefficient of that relation decreases exponentially with pO2, an equation can be derived that gives an excellent fit to the full range of the oxyhemoglobin dissociation curve. To generate this asymmetric sigmoid curve, only one rate constant is required. In addition, the initial and final conditions specify an intermediate constant B, the “shift factor” that determines the horizontal displacement of the curve. The rate constant K specifies the rate of change of the specific rate of increase of HbO2 with respect to O2. Governing the slope of the curve, K decreases as temperature and acidity increase, while the B factor remains constant. For Hb in solution, B decreases with decrease of concentration, but K appears to be unchanged. The expo-exponential constants provide convenient specification of the full course and position of the oxyhemoglobin dissociation curve. 相似文献
4.
《BBA》1986,849(3):337-346
A comparison of spectral properties of reaction centers from Chloroflexus aurantiacus and Rhodopseudomonas sphaeroides (R-26) is reported. Treatment of reaction centers from Rps. sphaeroides with NaBH4 leads to a decrease of the dipole strength of the 800-nm band by factor of approx. 1.75-1.95 and to the formation of new bacteriopheophytin, BPh-715, which is almost completely removed during the purification of reaction centers. The modification of the reaction centers does not change the quantum yield of P photooxidation and the spectrum of BPh-545 (H1) photoreduction which includes the changing of the 800-nm band. This implies the preservation of the photoactive chain P-B1-H1-QA (where B1 is the bacteriochlorophyll (BChl)-800 molecule situated between P and H1) and the modification of the second BChl-800 (B2). The preparation of modified reaction centers is a mixture of at least three types of reaction centers with different contents of B2 and of the second BPh (H2). Some of the reaction centers (5-25%) contain the original B2 and H2 molecules (type I). In the CD spectrum of modified reaction centers a decrease of the 800-nm band and the appearance of a positive band at 765 nm is observed. This spectrum is similar to the CD spectrum of Chloroflexus reaction centers containing 3 BPh's and 3 BChl's. This implies that in some (approx. 40%) of the modified Rps. sphaeroides reaction centers (type II) B2 has been replaced by BPh a which interacts with H2. Probably some of the modified reaction centers (approx. 40%) have lost both B2 and H2 (type III). The modification of reaction centers leads to a considerable decrease of the CD bands at 800 (+) nm and 810 (−) nm and to a decrease of the absorbance changes near 800 nm in the difference absorption spectrum of the oxidation of P. The data are interpreted in terms of the interaction between P and B1 molecules which gives two transitions at 790-800 and 810 nm with different orientations in modified Rps. sphaeroides as well as in Chloroflexus reaction centers. Similar transitions are observed for the interaction between P and B2. The spectral analysis shows the existence of two chains P-B1-H1, and P-B2-H2 in which the distances between the centers of molecules are 1.3 nm or less. 相似文献
5.
Allelopathy plays a crucial role in providing competitive advantage to several alien invasive species, and assists in their establishment beyond native boundaries. Role of allelopathy in the invasion success of the alien weed, Parthenium hysterophorus is well established; however, the ecological and evolutionary factors that could affect its allelopathic interactions are relatively unexplored. In our earlier findings, we suggested the presence of two morphotypes (PA and PB) in the population of P. hysterophorus, with variable morphology, physiology, and level of ecological impacts. Here, we hypothesize that phenotypically distinct morphotypes of P. hysterophorus may vary in their phytotoxicity and allelochemistry, thereby producing differential ecological impact. To test this hypothesis, effects of rhizospheric soil (RS) and plant amended soils (PAS) of the two morphotypes of P. hysterophorus (PA and PB) were studied on selected dicot (Bidens pilosa and Senna occidentalis) and monocot species (Phalaris minor and Avena fatua). Also, the composition of allelochemicals in PA and PB was assessed using Liquid Chromatography and Mass Spectrometry (LC-MS). The study revealed that the phytotoxic effect of PB was greater than PA in all the parameters measured for dicot species and in most of the parameters studied in monocot species. A generalized dose-dependent response was observed in the test species (PAS0 < PAS10 < PAS20 < PAS40) and the effect of RS was comparable to PAS20 and PAS40. A greater number of allelochemicals were reported from PB, which is in accordance with the growth studies. The study concludes that intraspecific variations account for differential phytotoxicity and allelochemistry in P. hysterophorus. 相似文献
6.
The effect of valinomycin on the electrical properties of solutions of red cell lipids in n-decane 总被引:1,自引:1,他引:0
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This paper reports the electrical properties of thick lipid membranes in the absence and presence of valinomycin. The thick lipid membranes were formed by placing a solution of sheep red cell lipids in decane between two cellophane partitions which formed the interfaces between the membrane and the two aqueous bathing solutions. The DC electrical resistance of these structures was found to be directly proportional to the reciprocal of the concentration of lipids in the decane (CL). The limiting resistance, as (CL
-1) approached zero, was 3 x 108 ohm-cm2. Resistance was also found to be linearly related to membrane thickness. The limiting resistance at zero thickness was again 1–3 x 108 ohm-cm2. These data are interpreted to indicate that the DC resistance of thick lipid membranes comprises two surface resistances (RS) at each interface with the aqueous bathing solutions, and a bulk resistance (RB) of the lipid-decane solution, arranged in series. Measurements of the effect of variations of area on resistance were consistent with this interpretation. Valinomycin reduced RS but had no effect on RB. Under certain conditions, thick lipid membranes containing valinomycin behaved like highly selective K+ electrodes. 相似文献
7.
L. A. Nesterova B. N. Manukhin 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2013,7(4):280-285
The influence of activation and inhibition of serotonin receptors by serotonin (5HT) and miancerin on binding of specific nonselective α2-antagonist [3H]RX821002 in rat cerebral cortex membranes was studied. It was shown that the ligand-receptor interaction for α2-adrenoceptors corresponded to the model suggesting the presence of one pool of receptors and binding of two ligand molecules to the receptor. The parameters of the [3H]RX821002 binding to α2-adrenoceptors were as follows: K d = 1.57 ± 0.276 nM, B max = 7.24 ± 1.63 fmol/mg protein, n = 2. In the case of activation of 5HT-receptors by serotonin, the character of ligand binding was different: two pools of receptors were detected with the parameters K d1 = 0.82 ± 0.06; K d2 = 2.65 ± 0.22 nM; B m1 = 1.65 ± 0.23; B m2 = 4.20 ± 0.11 fmol/mg protein; n = 2. The affinity of high-affinity receptors increased twofold and the affininty of low-affinity receptors decreased by 69% as compared to control values. The concentration of high-affinity receptors decreased 4.4-fold, and of low-affinity, 1.7-fold. The value of maximal reaction (B max) decreased by 20%. In the case of miancerin-induced inhibition of 5HT-receptors the character of ligand binding also changed; two pools of receptors were detected with the following parameters: K d1 = 0.48 ± 0.09; K d2 = 3.79 ± 0.71 nM; B 1 = 0.63 ± 0.17; B 2 = 4.75 ± 0.21 fmol/mg protein; n = 2. The affinity of high-affinity receptors pool increased by 70% and that of low-affinity receptors decreased by 76% as compared to control values. The concentration of active high-affinity and low-affinity α2-adrenoceptors decreased by 70% and 141%, respectively. The total amount of the receptors (B max) decreased by 26%. The data suggest that α2-adrenoceptors in rat cerebral cortex exist as dimers. Modulatory effects of serotonin and miancerin on specific antagonist binding to α2-adrenoceptors may be accomplished by altering the character and binding parameters of the nonselective α2-antagonist [3H]RX821002. 相似文献
8.
Sandra Hochscheid Flegra Bentivegna 《Journal of experimental marine biology and ecology》2003,297(2):123-140
Chelonian sea turtles use their lung as a buoyancy organ and as the major oxygen store when diving, and hence, buoyancy regulation and oxygen consumption can be expected to interact. The buoyancy of seven juvenile loggerhead turtles, Caretta caretta, was determined by measuring directly their underwater weight (Muw) while they were resting on a freely suspended weighing platform at a depth of 80 cm. Underwater weight was recorded continuously for 2 days for each turtle, followed by another 2 days measurements during which the turtles carried lead weights attached to their carapace, and finally, a last day of measurement after the weights had been removed. Total duration of resting dives (tr), buoyancy (FB), total resulting force acting on the resting turtle (Fres) and body volumes were derived from the Muw data. Turtles were slightly negatively buoyant when resting (Fres=−0.2943 to −0.981 N kg−1) and Muw increased significantly throughout each apnoeic period, meaning that the turtles progressively lost buoyancy. Pulmonary gas loss was calculated from the rate at which buoyancy decreased, which was significantly slower during the first half of the dive than during the second half of the dive. Resting oxygen consumption rates (VO2) were calculated from these data assuming that the pulmonary gas loss represents oxygen consumption from the lung. The VO2 obtained in this way (1.69-4.86 ml O2 min−1) corresponded well with other published and VO2 measured previously on loggerhead turtles in the same facility. Using oxygen from the lung affects buoyancy and may have impacts on the diving behaviour. 相似文献
9.
Models of diving optimality qualitatively predict diving behaviours of aquatic birds and mammals. However, none of them has been empirically tested. We examined the quantitative predictions of optimal diving models by combining cumulative oxygen uptake curves with estimates of power costs during the dives of six tufted ducks, Aythya fuligula. The effects of differing foraging costs on dive duration and rate of oxygen uptake (VO2up) at the surface were measured during bouts of voluntary dives to a food tray. The birds were trained to surface into a respirometer after each dive, so that changes in VO2up over time could be measured. The tray held either just food or closely packed stones on top of the food to make foraging energetically more costly. In contrast to predictions from the Houston & Carbone model, foraging time (tf) increased after dives incorporating higher foraging energy costs but surface time (ts) remained the same. While optimal diving models have assumed that the cumulative oxygen uptake curve is fixed, VO2up increased when the energy cost of the dive increased. The optimal breathing model quantitatively predicted ts in both conditions and oxygen consumption during foraging (m2tf) in the control condition, for the mean of all ducks. This offers evidence that the ducks were diving optimally and supports the fundamentals of optimal diving theory. However, the model did not consistently predictts or m2tf for individual birds. We discuss the limits of optimal foraging models for air-breathing divers caused by individual variation. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour. 相似文献
10.
Sofia Gallo 《Inorganica chimica acta》2007,360(1):360-368
The organometallic complex coenzyme B12 (adenosyl cobalamin, AdoCbl) is not only an essential coenzyme in many biochemical reactions of most if not all living organisms but has lately been shown to play a crucial role in the regulation of B12 related genes. As a consequence, coenzyme B12 has been a target of intense research. However, the investigations of AdoCbl have often been hampered due to its high light-sensitivity leading to decomposition of the compound within a few seconds. Here, we describe a strategy to synthesize more light-stable coenzyme B12 analogs, which show similar steric properties as adenosyl cobalamin. The synthesis, structural characterization as well as the pH dependent “base-on/base-off” behavior of cyanide bridged vitamin B12 conjugates with either a cis-[(NH3)2Pt]2+ or an [enPt]2+ moiety, leading to cis-[(NH3)2PtCl-vitB12]+ (1) and [enPtCl-vitB12]+ (2) are reported. The subsequent reaction of cis-[(NH3)2PtCl-vitB12]+ with the model nucleobase 9-methyladenine leads to the corresponding adduct, where the adenine moiety is coordinated to the Pt2+ center either via N1 or N7. This compound is light-stable and harbors the adenine moiety in the same distance of 5 Å above the corrin plane as present in the highly light-sensitive adenosyl cobalamin. 相似文献
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12.
Vinay Singh Tanwar Mandeep P. Chand Jitender Kumar Gaurav Garg Sandeep Seth Ganesan Karthikeyan Shantanu Sengupta 《Gene》2013
Vitamin B12 is an essential micronutrient synthesized by microorganisms. Mammals including humans have evolved ways for transport and absorption of this vitamin. Deficiency of vitamin B12 (either due to low intake or polymorphism in genes involved in absorption and intracellular transport of this vitamin) has been associated with various complex diseases. Genome-wide association studies have recently identified several common single nucleotide polymorphisms (SNPs) in fucosyl transferase 2 gene (FUT2) to be associated with levels of vitamin B12—the strongest association was with a non-synonymous SNP rs602662 in this gene. In the present study, we attempted to replicate the association of this SNP (rs602662) in an Indian population since a significant proportion has been reported to have low levels of vitamin B12 in this population. A total of 1146 individuals were genotyped for this SNP using a single base extension method and association with levels of vitamin B12 was assessed in these individuals. Regression analysis was performed to analyze the association considering various confounding factors like for age, sex, diet, hypertension, diabetes mellitus and coronary artery disease status. We found that the SNP rs602662 was significantly associated with the levels of vitamin B12 (p value < 0.0001). We also found that individuals adhering to a vegetarian diet with GG (homozygous major genotype) have significantly lower levels of vitamin B12 in these individuals. Thus, our study reveals that vegetarian diet along with polymorphism in the FUT2 gene may contribute significantly to the high prevalence of vitamin B12 deficiency in India. 相似文献
13.
Mohammed A. Farid Eglal A. Ghoneimy Maie A. El-Khawaga Asmaa Negm-Eldein Ghada E. A. Awad 《Annals of microbiology》2013,63(2):523-531
Response surface methodology (RSM), employing the fractional factorial design (FFD) was used to optimize the fermentation medium for the production of glucose oxidase (GOD) from a marine isolate (NRC9) of Aspergillus niger under submerged fermentation. The design was employed by selecting glucose, CaCO3, ammonium phosphate and MgSO4 concentrations as model factors by ‘one variable at a time’ experiment. A second-order quadratic model and response surface method showed that the optimum concentrations (g/l) glucose, 100; CaCO3, 25; (NH4)2HPO4, 1.8 and 0.4 of MgSO4, resulted in an improvement of GOD production (170?±?0.88 U/ml) as compared to the initial level (109.81?±?1.38 U/ml) after four days of incubation at 200 rpm and 30 °C, whereas its predicted value obtained by the quadratic model was 164.36 U/ml. Analysis of variance (ANOVA) showed a high coefficient of determination value (R 2) of 0.967, ensuring a satisfactory adjustment of the quadratic model with the experimental data. This is the first report on production of glucose oxidase from a marine fungal isolate, Aspergillus niger NRC9, using statistical experimental design and response surface methodology in optimization of its production under submerged fermentation. 相似文献
14.
L. A. Nesterova B. N. Manukhin 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2013,7(1):45-51
The effects of activation and inhibition of serotonin receptors by serotonin (5-HT) and mianserin on the specific nonselective α1-antagonist [3H]prazosine binding in rat cerebral cortex membranes was studied. It was shown that the ligand-receptor interaction of α1-adrenoceptors corresponded to the model suggesting the presence of one pool of receptors and the binding of two ligand molecules to the receptor. The parameters of [3H]prazosine binding to α1-adrenoceptors were as follows: K d =1.85 ± 0.16 nM, B max = 31.1 ± 0.3 fmol/mg protein, n = 2. In case of activation of 5HT-receptors by serotonin, the character of ligand binding was different: two pools of receptors were detected with the parameters K d1 = 0.61 ± 0.04, K d2 = 3.82 ± 0.15 nM, B m1 = 6.6 ± 0.7, B m2 = 25.6 ± 0.4 fmol/mg protein, n = 2. The sensitivity of the high-affinity pool increased threefold and the sensitivity of the low-affinity pool decreased twofold as compared to the control. The value of maximal reaction (B max) did not change. In the case of inhibition of 5HT-receptors by mianserin, radioactive ligand is bound to α1-adrenoceptors according to the same model as in the control conditions. The affinity of α1-adrenoceptors to [3H]prazosine decreases twofold and the concentration increases (K d = 3.97 ± 0.12 nM, B max = 40.0 ± 0.5 fmol/mg protein). The data suggest that α1-adrenoceptors in rat cerebral cortex exist as a dimer. The modulatory effects of serotonin and mianserin on the specific binding of [3H]prazosine to α1-adrenoceptors was detected, manifesting itself as changes in the binding parameters and in the general character of ligand-receptor interactions. 相似文献
15.
《Inorganica chimica acta》1987,128(1):27-29
2′-Deoxy-5′-guanosinemonosphoric acid (B) reacts with cis-[Pt(NH3)2(OH2)2]2+ in two steps to form the cis-[Pt(NH3)2B2]y+ ion. In the first step 2′-d-5′- GMPH2 reacts some ten times faster than 5′-GMPH2 does. Rate constants, ΔH#, ΔS# and ΔV# are very similar for the two bases in the second reaction. It is proposed that the product in the first step contains no water and is cis-[Pt(NH3)2B]x+ in which the nucleobase is bidentate bonding through both N(7) of guanine and an oxygen atom of the phosphate group. 相似文献
16.
Cytochrome ba3 (ba3) of Thermus thermophilus (T. thermophilus) is a member of the heme–copper oxidase family, which has a binuclear catalytic center comprised of a heme (heme a3) and a copper (CuB). The heme–copper oxidases generally catalyze the four electron reduction of molecular oxygen in a sequence involving several intermediates. We have investigated the reaction of the fully reduced ba3 with O2 using stopped-flow techniques. Transient visible absorption spectra indicated that a fraction of the enzyme decayed to the oxidized state within the dead time (~ 1 ms) of the stopped-flow instrument, while the remaining amount was in a reduced state that decayed slowly (k = 400 s? 1) to the oxidized state without accumulation of detectable intermediates. Furthermore, no accumulation of intermediate species at 1 ms was detected in time resolved resonance Raman measurements of the reaction. These findings suggest that O2 binds rapidly to heme a3 in one fraction of the enzyme and progresses to the oxidized state. In the other fraction of the enzyme, O2 binds transiently to a trap, likely CuB, prior to its migration to heme a3 for the oxidative reaction, highlighting the critical role of CuB in regulating the oxygen reaction kinetics in the oxidase superfamily. This article is part of a Special Issue entitled: Respiratory Oxidases. 相似文献
17.
Donghwan Park MyungJa Ro A-Jin Lee Dong-Wook Kwak Yunro Chung Jae-Hong Kim 《Molecules and cells》2021,44(12):893
BLT2 is a low-affinity receptor for leukotriene B4, a potent lipid mediator of inflammation generated from arachidonic acid via the 5-lipoxygenase pathway. The aim of this study was to investigate whether BLT2 plays any role in sepsis, a systemic inflammatory response syndrome caused by infection. A murine model of cecal ligation and puncture (CLP)-induced sepsis was used to evaluate the role of BLT2 in septic inflammation. In the present study, we observed that the levels of ligands for BLT2 (LTB4 [leukotriene B4] and 12(S)-HETE [12(S)-hydroxyeicosatetraenoic acid]) were significantly increased in the peritoneal lavage fluid and serum from mice with CLP-induced sepsis. We also observed that the levels of BLT2 as well as 5-lipoxygenase (5-LO) and 12-LO, which are synthesizing enzymes for LTB4 and 12(S)-HETE, were significantly increased in lung and liver tissues in the CLP mouse model. Blockade of BLT2 markedly suppressed the production of sepsis-associated cytokines (IL-6 [interleukin-6], TNF-α[[tumor necrosis factor alpha], and IL-1β [interleukin-1β] as well as IL-17 [interleukin-17]) and alleviated lung inflammation in the CLP group. Taken together, our results suggest that BLT2 cascade contributes to lung inflammation in CLP-induced sepsis by mediating the production of inflammatory cytokines. These findings suggest that BLT2 may be a potential therapeutic target for sepsis patients. 相似文献
18.
The frequency distribution of diameter (x) in foliage shoot segments, ø(x), was examined in 18 branches at different height levels of three trees in a 25-yr-old sugi (Cryptomeria japonica D. Don) plantation. The ø-x relationships were approximated by power-form equations, in which the exponent differed among the branches from ?0.6 to ?4.2. Leaf area (S B) and leaf weight (W B) of a branch were estimated on the basis of the ø-x relationship, and the dependency of specific leaf area (SLA 0) and density (ρ 0) of a foliage shoot segment on itsx. SLA B value of a branch defined byS B/W B ranged from 27 to 80 cm2 g. d.w.?1 according to the exponent in the function of ø(x). Total leaf area (u) and leaf weight (wl) of a tree were estimated by summation ofS B andW B for seven sample trees. TheSLA T value of a tree defined byu/wl ranged from 65 to 76 cm2 g d.w.?1 and increased with stem diameter at clear length (D B). By use of the allometric equations betweenu andD B,LAI of the plot was estimated to be 17.3 ha ha?1 (half of the total surface area of needles). By a process similar to that used for calculatingLAI, the amount of woody tissues included in sugi foliage was evaluated to be about 10% of the stand foliage biomass. 相似文献
19.
Sodium Chloride Reduces Production of Curvacin A, a Bacteriocin Produced by Lactobacillus curvatus Strain LTH 1174, Originating from Fermented Sausage 总被引:1,自引:0,他引:1
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Lactobacillus curvatus LTH 1174, a strain originating in fermented sausage, produces the antilisterial bacteriocin curvacin A. Its biokinetics of cell growth and bacteriocin production as a function of various concentrations of salt (sodium chloride) were investigated in vitro during laboratory fermentations using modified MRS medium. A model was set up to describe the effects of different NaCl concentrations on microbial behavior. Both cell growth and bacteriocin activity were affected by changes in the salt concentration. Sodium chloride clearly slowed down the growth of L. curvatus LTH 1174, but more importantly, it had a detrimental effect on specific curvacin A production (kB) and hence on overall bacteriocin activity. Even a low salt concentration (2%, wt/vol) decreased bacteriocin production, while growth was unaffected at this concentration. The inhibitory effect of NaCl was mainly due to its role as an aw-lowering agent. Further, it was clear that salt interfered with bacteriocin induction. Additionally, when 6% (wt/vol) sodium chloride was added, the minimum biomass concentration necessary to start the production of curvacin A (XB) was 0.90 g (cell dry mass) per liter. Addition of the cell-free culture supernatant or a protein solution as a source of induction factor resulted in a decrease in XB, an increase in kB, and hence an increase in the maximum attainable bacteriocin activity. 相似文献
20.
Mesophyll Resistance and Carboxylase Activity: A Comparison under Water Stress Conditions 总被引:6,自引:4,他引:2
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The response of several leaf gas exchange parameters were monitored with decreasing leaf water potential in Phaseolus vulgaris L. leaflets. These included photosynthesis, transpiration, CO2 compensation point, ribulose 1,5-diphosphate carboxylase activity, boundary layer plus stomatal, and mesophyll resistance to diffusion of CO2. Mesophyll resistance was calculated under two assumptions: (a) the CO2 concentration at the chloroplast was zero, and (b) it was equal to the CO2 compensation point. 相似文献