共查询到20条相似文献,搜索用时 31 毫秒
1.
Davood Ajloo Ali A. Saboury Niloofar Haghi-Asli Ghasem Ataei-Jafarai Ali A. Moosavi-Movahedi Mosayeb Ahmadi 《Journal of enzyme inhibition and medicinal chemistry》2013,28(4):395-406
The kinetic and thermodynamic effects of aspirin and diclofenac on the activity of adenosine deaminase (ADA) were studied in 50 mM phosphate buffer pH = 7.5 at 27 and 37°C, using UV-Vis spectrophotometry and isothermal titration calorimetry (ITC). Aspirin exhibits competitive inhibition at 27 and 37°C and the inhibition constants are 42.8 and 96.8 μM respectively, using spectrophotometry. Diclofenac shows competitive behavior at 27°C and uncompetitive at 37°C with inhibition constants of 56.4 and 30.0 μM, at respectively. The binding constant and enthalpy of binding, at 27°C are 45 μM, ? 64.5 kJ/mol and 61 μM, ? 34.5 kJ/mol for aspirin and diclofenac. Thermodynamic data revealed that the binding process for these ADA inhibitors is enthalpy driven. QSAR studies by principal component analysis implemented in SPSS show that the large, polar, planar, and aromatic nucleoside and small, aromatic and polar non-nucleoside molecules have lower inhibition constants. 相似文献
2.
E. Sánchez R. Borja P. Weiland L. Travieso A. Martín 《Bioprocess and biosystems engineering》2000,22(3):247-252
A study of the effect of temperature and pH on the kinetics of methane production and organic nitrogen and phosphorus degradation in the anaerobic digestion process of cattle manure was carried out. Two laboratory-scale batch completely mixed reactors, operating at 35v°C (mesophilic temperature), and other two, operating at 60v°C (thermophilic temperature) were used. For each temperature selected, the influent pH values were 7.6 (initial pH of the waste used) and 7.0. The apparent kinetic constants of the biomethanization process increased 2.3 times when the initial pH of the influent was increased from 7.0 to 7.6 at mesophilic temperature. The values found at thermophilic temperature were similar. The kinetic constants of methane production decreased 2.6 and 7.2 times when the operating temperature increased from 35 °C to 60v°C for the experiments carried out at initial pH of 7.0 and 7.6, respectively. The methane yield coefficient (l CH4 STP/g VS removed) also decreased when the temperature increased from 35v°C to 60v°C for the two initial pH values studied. This behaviour agreed with the major inhibition level observed at thermophilic temperature as a result of the higher organic nitrogen removal and ammonia nitrogen production observed at 60v°C. Specifically, the specific rate constants for organic nitrogen removal and ammonia nitrogen production increased 3.6 and 12 times when the temperature was increased from 35v°C to 60v°C for the experiments carried out at initial pH values of 7.0 and 7.6, respectively. In the same way, the values of the kinetic constant for phosphorus removal were 44% and 80% higher than those obtained at 35v°C for the two initial pH values above-mentioned, respectively. Finally, the experimental values of organic nitrogen and phosphorus concentrations were reproduced with deviations equal to or less than 10% and 15% in every case, respectively. 相似文献
3.
H H Paradies 《Biochemical and biophysical research communications》1979,88(3):810-817
The formation of aggregates of tyrocidine B at 4°C and 20°C in aqueous solutions was studied by means of light scattering and fluorescent techniques. The apparent weight molecular weight of tyrocidine B aggregates was found to be 36,000 at 4°C and 28,800 at 20°C. Fluorescence titration experiments with dansyl-chloride resulted in an aggregational number of 31 (4°) and 28 (20°) indicating that one molecule of dye is bound per monomer of molecular weight 1,200. From a Scatchard plot apparent association constants of 1.22 × 105 M (4°) and 0.95 × 105 M (20°) were calculated. From the angular dependence of scattered intensity the radii of gyration were determined to be 60 Å and 58 Å, respectively. 相似文献
4.
The conformation of the sugar moiety of 8-(N-fluoren-2-ylamino)-2′-deoxyguanosine in solution has been examined as a function of temperature by 1H-nmr spectroscopy. Analysis of coupling constants shows that lowering the temperature to ?50°C in methanol shifts the conformational equilibrium of the sugar ring resulting in a C2′-endo conformation at a mole fraction of 0.97. The computed phase angle of pseudorotation and amplitude of pucker are 154° and 36°, respectively, with very little discrepancy between the five calculated coupling constants and coupling constants extrapolated from the temperature profiles. A computer program has been written enabling a three-state best-fit analysis. The three-state analysis indicates an equilibrium between C2′-endo, C3′-endo, and 04′-endo conformations. In aqueous solution, the computed mole fraction of the 04′-endo form is 0.18 at 30°C. The conformation associated with the sugar ring and the C4′? C5′ bond is compared to that of 2′-deoxyguanosine. 相似文献
5.
Isozymic banding patterns and energies of activation were studied in partially puriled G6PDH preparations from spring and fall Rana pipiens eggs and tadpoles raised at 10 °C and 20 °C.G6PDH preparations from spring tadpoles raised at 20 °C demonstrated new isozyme patterns. However, in the spring 10 °C and fall 10 °C and 20 °C raised tadpoles G6PDH preparations conserved isozymes already present.The energies of activation of G6PDH determined from the maximum velocity constants in the spring groups are lower than in the corresponding fall groups. 相似文献
6.
Hannah Friedman Elson 《Journal of cellular biochemistry》1979,10(1):39-50
Acetylcholine receptors were assayed with α-bugarotoxin on embryonic chick skeletal muscle growing in primary cell culture. Toxin was bound specifically to muscle cells and could be competed with D-tubocurarine. Two dissociation constants were obtained by equilibrium binding: 7.2 × 10?9M and 2.7 × 10?7M at 25°C. Two sets of rate constants were also obtained from dissociation kinetics. There are five times more low affinity sites on cells than high affinity sites. The average density of high-affinity receptors is about 200/μm2. A time course of toxin binding to receptors at 37°C vs 25°C in growth medium revealed that under conditions permitting growth and metabolism, toxin bound to cells was lost. The possibility that the growth medium was in-activating toxin molecules was ruled out by showing that unbound toxin molecules in the medium were fully capable of binding to fresh cultures. 相似文献
7.
Interactions which determine the rate of conversion of fibrinogen into monomer fibrin and the retention of monomer fibrin in a noncompactible form through interaction with residual fibrinogen (solution stabilization) were examined through the kinetics of formation of equilibrium compactible network at pH 7 and ionic strength 0.15. For studies of conversion, reactions with thrombin were at 29 or 2 °C, hirudin was added at successive times to inhibit thrombin, and compactible network was equilibrated at 2 °C, where solution stabilization is negligible. A substrate dependency of initial rate is interpreted on the basis of inactive complex formation between thrombin and both fibrinogen and monomer fibrin. At 29 or 2 °C specific rate constants are 32 or 2.9 × 106 liter/mol, and association constants for inactive complex formation are 5.2 or 2.0 × 105 liter/mol. The second peptide-A is removed from fibrinogen ~ 40-fold as rapidly as the first.With equilibration at 29 °C, compactible network does not appear until the solution stabilization ratio of residual fibrinogen/monomer fibrin is four. Thereafter, increasing amounts of compactible network appear. However, the stabilization ratio progressively decreases to approximately two, a situation which indicates the complexity of the stabilization mechanism.The thrombin-hirudin association constant is estimated to be 4.9 or 17 × 1011 liter/mol at 29 or 2 °C. 相似文献
8.
Shu‐Qin Lian Jie Lian Gui‐Rong Wang Lin Li Dong‐Zhi Yang Yun‐sheng Xue 《Luminescence》2019,34(6):595-601
In this paper, the interactions of pepsin with fluoroquinolones, including norfloxacin (NFX) or ofloxacin (OFX), were investigated using fluorescence spectroscopy. The effects of NFX or OFX on pepsin showed that the molecular conformation of pepsin and the microenvironment of tryptophan residues were changed under mimicked physiological conditions. Static quenching was suggested as a factor. Quenching constants and binding constants were determined and thermodynamic parameters were calculated at three temperatures (25°C, 31°C and 37°C). Molecular interaction distances (binding distance r) were obtained. Binding was enthalpy driven and the process was spontaneous. Synchronous fluorescence, three‐dimensional fluorescence spectroscopy and molecular simulation were used for analysis. Interactions were further tested using molecular modelling. Quenching and binding constants of NFX with pepsin were the highest when testing NFX/OFX/fleroxacin/gatifloxacin with pepsin combinations. NFX was the strongest quencher, and affinity of NFX for pepsin was higher than that of OFX/fleroxacin/gatifloxacin. 相似文献
9.
Pyrethroid modulation of sodium channels is unique in the sense that it is highly dependent on temperature, the potency being
augmented by lowering the temperature. To elucidate the mechanisms underlying the negative temperature dependence of pyrethroid
action, single sodium channel currents were recorded from cultured rat hippocampal neurons using the inside-out configuration
of patch-clamp technique, and the effects of the pyrethroid tetramethrin were compared at 22 and 12°C. Tetramethrin-modified
sodium channels opened with short closures and/or transitions to subconductance levels at 22 and 12°C. The time constants
of the burst length histograms for tetramethrin-modified channels upon depolarization to −60 mV were 7.69 and 14.46 msec at
22 and 12°C, respectively (Q10= 0.53). Tetramethrin at 10 μm modified 17 and 23% of channels at 22 and 12°C, respectively, indicating that the sensitivity of the sodium channel of rat
hippocampal neurons to tetramethrin was almost the same as that of tetrodotoxin-sensitive sodium channels of rat dorsal root
ganglion neurons and rat cerebellar Purkinje neurons. The time constants for burst length in tetramethrin-modified sodium
channels upon repolarization to −100 mV from −30 mV were 8.26 and 68.80 msec at 22 and 12°C (Q10= 0.12), respectively. The prolongation of tetramethrin-modified whole-cell sodium tail currents upon repolarization at lower
temperature was ascribed to a prolongation of opening of each channel. Simple state models were introduced to interpret behaviors
of tetramethrin-modified sodium channels. The Q10 values for transition rate constants upon repolarization were extremely large, indicating that temperature had a profound
effect on tetramethrin-modified sodium channels.
Received: 31 January 2000/Revised: 18 May 2000 相似文献
10.
The kinetics of the Cu(II) catalysed hydrolysis of thiamine-pyrophosphate (TPP) has been studied in aqueous solution at 56,64 and 78° over a pH fange of 3.0 to 7.0 at a constant ionic strength of 0.10 M (KNO3). The pH rate profiles were analysed and the overall rate constants resolved into individual specific rate constants relating to various Cu:TPP chelate species in solution. Activation parameters ΔH2, ΔS° and ΔG2 for the specific rate constants of various chelate species of TPP are reported. The possible mechanism of the Cu(II) promoted hydrolysis of TPP is discussed. The structure-reactivity relationship is also discussed. 相似文献
11.
Richard W. Briggs George K. Radda Keith R. Thulborn 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1985,845(3):343-348
The kinetics of the reaction catalyzed by arginine kinase have been determined at 9.5 and 23°C for in vivo leg muscle of Carcinus maenas (the common shore crab) using the noninvasive technique of 31P-NMR spectroscopy. Concentrations of mobile phosphorus metabolites were the same at both temperatures: 78.7 mM for arginine phosphate, 9.0 mM for adenosine triphosphate (ATP), and 2.6 mM for inorganic phosphate (Pi), as estimated from NMR resonance intensities and literature values for ATP concentration as assayed by traditional biochemical methods. Apparent unidirectional rate constants for formation of ATP from arginine phosphate and ADP were 0.09 s?1 at 9.5°C and 0.27 s?1 at 23°C. Pseudo-first-order rate constants for arginine phosphate generation from Arg and ATP were 0.38 and 1.10 s?1 at 9.5 and 23°C, respectively. In vivo Q10 for the arginine kinase reaction between 9.5 and 23°C was thus 2.2 for both directions. When the kinetic data are analyzed using the Arrhenius equation, activation energies of 126 kJ/mol for ATP formation and 105 kJ/mol for arginine phosphate formation are found. The measured chemical fluxes through arginine kinase in the forward reaction (arginine phosphate hydrolysis) were twice those in the reverse reaction, consistent with either compartmentation of substrates or participation of substrates in alternative metabolic pathways. 相似文献
12.
The removal of cobalt from cobalt(II) bovine carbonic anhydrase by pyridine-2-carboxylate, pyridine-2,6-dicarboxylate and 5-methyl-1,10-phenanthroline occurs via formation of an intermediate. This is presumed to be a ternary adduct of cobalt(II) enzyme with the ligand. In this, metal-protein bonds are loosened, probably via distortion of the normal geometry, resulting in accelerated breakdown of the adduct to apoprotein, compared with the behavior of the cobalt(II) enzyme alone. With 2-carboxy-1,10-phenanthroline, removal of metal is very rapid but no adduct is observed. Values of stability constants of the adducts and rate constants for their decomposition to apoprotein and their formation from apoprotein and cobalt(II) complex were measured at pH 5.5 and 25°C. Formation and dissociation rate constants for the adduct of cobalt carbonic anhydrase with pyridine-2,6-dicarboxylate could be measured from pH 5 to 7 and 10° to 25°C by stopped flow. Values of thermodynamic parameters for the various reactions agreed well with those estimated from the kinetic data. 相似文献
13.
Helix-coil dynamics of a Z-helix hairpin 总被引:1,自引:0,他引:1
The helix–coil transition of a Z-helix hairpin formed from d(C-G)5T4(C-G)5 has been characterized by equilibrium melting and temperature jump experiments in 5M NaClO4 and 10 mM Na2HPO4, pH 7.0. The melting curve can be represented by a simple all-or-none transition with a midpoint at 81.6 ± 0.4°C and an enthalpy change of 287 ± 15 kJ/mole. The temperature jump relaxation can be described by single exponentials at a reasonable accuracy. Amplitudes measured as a function of temperature provide equilibrium parameters consistent with those derived from equilibrium melting curves. The rate constants of Z-helix formation are found in the range from 1800 s?1 at 70°C to 800 s?1 at 90°C and are associated with an activation enthalpy of ?(50 ± 10) kJ/mole, whereas the rate constants of helix dissociation are found in the range from 200 s?1 at 70°C to 4500 s?1 at 90°C with an activation enthalpy +235 kJ/mole. These parameters are consistent with a requirement of 3–4 base pairs for helix nucleation. Apparently nucleation occurs in the Z-helix conformation, because a separate slow step corresponding to a B to Z transition has not been observed. In summary, the dynamics of the Z-helix–coil transition is very similar to that of previously investigated right-handed double helices. 相似文献
14.
G. Annadurai R. Y. Sheeja S. Mathalai Balan T. Murugesan V. R. Srinivasamoorthy 《Bioprocess and biosystems engineering》1999,20(1):37-43
Equilibrium conditions in the adsorption of a basic dye on Chitosan were studied. The Factorial Design methods and Analysis of Variance have been applied in the experimental determination of adsorption equilibrium constants. Factorial design with three levels of temperature (30v°C, 45v°C, 60v°C), pH (6.7, 8.1, 9.5), particle size (0.177 mm, 0.914 mm, 1.651 mm) was used in identification of significant effects and interactions in the calculation of the equilibrium constants. The dye adsorption capacity of chitosan was found to increase by decreasing the particle size and increasing temperature and pH. The methodology identifies the principal experimental variables, which have the greatest effect on the adsorption process. 相似文献
15.
Biochemical properties of the 1 alpha, 25-dihydroxyvitamin D3 cytoplasmic receptors from human and chick parathyroid glands 总被引:3,自引:0,他引:3
W R Wecksler F P Ross R S Mason S Posen A W Norman 《Archives of biochemistry and biophysics》1980,201(1):95-103
Cytoplasmic receptors for 1α, 25-dihydroxyvitamin D3 from human parathyroid adenoma tissue and rachitic chick parathyroid glands have been characterized with regard to a number of physical, chemical, and ligand binding properties. Both receptors are 3.6–3.7 S proteins with molecular weights of approximately 75,000 and Stoke's molecular radii of 36 Å. It was found that the receptors possess a cysteine residue in or near the 1α, 25-dihydroxyvitamin D3 binding site which is critical for ligand binding activity. The receptors both have equilibrium dissociation constants for 1α, 25-dihydroxyvitamin D3 in the range of 2 to 5 × 10?10m at 4 °C and second-order association rate constants for their seco-steroid ligand of 1 × 107, m?1 min?1 (0 °C). The dissociation rate constants were found to be 5.3 × 10?4 min?1 (4 °C) for the human receptor and 1.3 × 10?5 min?1 (4 °C) for the chick receptor. The great deal of similarity which exists between the cytoplasmic 1α, 25-dihydroxyvitamin D3 receptors from avian and mammalian parathyroid glands suggests a homologous function for these molecules in the two tissues. 相似文献
16.
J L Meyer 《Analytical biochemistry》1974,62(1):295-300
Formation constants for the interaction of citrate ion with calcium and magnesium ions in solution at 37°C and a constant ionic strength of 0.15 were determined by potentiometric titration. Values for the formation of CaL? and CaHL0 complexes were 1.88 × 103 and 67, respectively. Corresponding constants for MgL? and MgHL0 were 2.19 × 103 and 42, respectively. The existence of other complexes was not confirmed. Protonation constants were also determined under the same conditions. 相似文献
17.
Ŝtefan Janeĉek Ŝtefan Baláž Michal Rosenberg Miroslav Stredanský 《Biotechnology Techniques》1992,6(2):173-176
Summary Thermostability ofBacillus subtilis α-amylase at 70°C and higher temperatures is increased by its modification with D-glucono-δ-lactone, regardless whether the
modification reaction proceeds in the presence or absence of the substrate. The pH-profile of the spontaneous hydrolysis of
the modifier was determined with the aim of finding the optimal modification conditions. The Arrhenius plot of the inactivation
rate constants exhibits the isokinetic effect, with the temperature of compensation being approximately 63°C. 相似文献
18.
To explore the possibility of usingOrius tantillus (Motschulsky) as a control agent againstThrips palmi Karny in greenhouses in Japan during the winter months, the effects of temperature on the development of eggs and nymphs of this predator were determined by rearing individuals under eight constant temperatures ranging from 17.5–35.0°C. Estimates of lower developmental threshold temperatures for eggs, male nymphs and female nymphs were 13.7°C, 11.9°C and 13.4°C, respectively. These estimates were lower than the average winter temperature at night in greenhouses in Japan, suggesting thatO. tantillus could possibly be used for the control ofT. palmi in such greenhouses. Thermal constants were estimated at 52.6, 185.2 and 153.8 degree days for eggs, male nymphs and female nymphs, respectively. Egg survival at temperatures between 20°C and 30°C was higher (p=0.05) than at 17.5°C. 相似文献
19.
The equilibrium constants and rate constants for the formation of azo dye-cyclomaltohexaose complexes have been determined at 26.6° and an ionic strength of 0.15. The effect of changing the substituents on the dyes is explained in terms of the sizes (steric factors) of the substituents and the charges on the substituents 相似文献
20.
Interaction of epidermal growth factor with adult rat liver parenchymal cells in primary culture 总被引:5,自引:0,他引:5
Adult rat liver parenchymal cells in primary culture exhibit specific saturable binding of 125I-labeled murine epidermal growth factor (EGF). The Scatchard plot of the binding data obtained at 36 °C was curvilinear yielding two apparent dissociation constants of 1.5 × 10?10m and 1.2 × 10?9m with 27,000 and 57,000 sites per cell, respectively. The binding data obtained at 2 °C yielded a linear Scatchard plot with an apparent dissociation constant of 4.4 × 10?9m and 78,000 sites per cell. Exposure of the hepatocytes to EGF at 36 °C resulted in a loss of EGF binding capacity due to down regulation of receptors. The cells recovered the capacity to bind EGF upon incubation in medium which did not contain EGF; this recovery was inhibited by cycloheximide. The cultures appeared to internalize and degrade bound EGF at 36 °C but not at 2 °C. The degradation of EGF was inhibited by chloroquine, an inhibitor of lysosomal enzymes. These data indicate that liver specifically binds and further processes EGF, and therefore, may be a physiological target tissue for this growth factor. 相似文献