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1.
The effect of three kinds of selenide on Staphylococcus aureus growth was studied by means of microcalorimetry. Differences in their capacities to inhibit the metabolism of this bacterium were observed. The rate constant k (in the log phase) in the presence of the compounds decreased with increasing concentrations of the compounds. The relationship of k and c is nearly linear for the selenium compounds. Judged from the rate constant, k, and the half-inhibitory concentration IC50, the experimental results reveal that the sequence of antibiotic activity of the three tested selenides compounds is (2-hydroxy benzyl imino)ethyl n-hexyl selenide> n-butyl(2- hydroxy benzyl imino)ethyl selenide > bis[(2,4-dihydroxy benzyl imino)ethyl] selenide. 相似文献
2.
The actions of two novel diselenide-bridged bis(porphyrin)s (1 and 2) on Staphylococcus aureus growth was investigated by microcalorimetry at 37.00°C, compared with that of Na2SeO3. Differences in their capacities to inhibit the growth metabolism of S. aureus were observed. By analyzing the power–time curves, crucial parameters such as the rate constant of bacterial growth (k), inhibitory rate (I), and generation time (t
G) were determined. The growth rate constant (k) of S. aureus (in the log phase) in the presence of the drugs decreased with increasing concentrations of the drugs regularly. The relationship
of k and c is nearly linear for diselenide-bridged bis(porphyrin) 2. The sequence of the antibacterial activities of these selenium compounds tested was 2 > 1 > Na2SeO3. 相似文献
3.
Xu XJ Chen CQ Wang ZY Zhang Y Hou AX Li CH Liu Y 《Biological trace element research》2009,127(3):269-277
The antibacterial effect of Zn(II), tetraphenyl porphyrin (TPP), propdioxyl bridged tetraphenyl bisporphyrin 1, and its metallobisporphyrin complexes (ZnMnbisporphyrin 2 and ZnZnbisporphyrin 3) towards Staphylococcus aureus growth was investigated by microcalorimetry at 37°C. Differences in their capacities to inhibit the growth metabolism of
S. aureus were observed. By analyzing the power–time curves, crucial parameters such as the rate constant of bacterial growth (k), inhibitory ratio (I), and generation time (t
G) were determined. The growth rate constant (k) of S. aureus (in the log phase) in the presence of the drugs decreased linearly with increasing concentrations of the complexes. The sequence
of the antibacterial activities of these compounds tested was 3 > 2 > 1 > Zn(II) > TPP. ZnZnbisporphyrin 3 is proposed to benefit from the synergetic effects of Zn(II) and 1. 相似文献
4.
The inhibitory or antibiotic action of four kinds of the selenomorpholine complex on a strain of Escherichia coli was studied by microcalorimetry. Differences in their capacities to inhibit the metabolism of this bacterium were observed.
The extent and duration of the inhibitory effect on the metabolism as judged from the rate constant, k, and the half-inhibitory concentration, IC50, varied with the different drugs. The rate constant (k) of Escherichia coli (in the log phase) in the presence of the drugs decreased with increasing concentrations of the drugs (C). The relationship of k and C is nearly linear for (1) selenomorpholine and (2) selenomorpholine hydrochloride, but for (3) N,N′-methylene bisselenomorpholine and (4) N-dodecyl selenomorpholine, it is not linear. The experimental results reveal that the sequence of antibiotic activity of selenomorpholines
is (3) and (4)>(1)>(2). 相似文献
5.
A comparison of acylation, phosphorylation and binding in related substrates and inhibitors of serum cholinesterase
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1. The Km and catalytic-centre activities for human serum cholinesterase and methyl, ethyl, n-propyl and n-butyl butyrate substrates were determined and compared with the related inhibition constants of a similarly substituted organophosphate inhibitor series based on malaoxon. The results indicated that the catalytic-centre activities approximated to k+2(a), the acylation rate constant, and that Km approximated to the equilibrium binding constant. The inhibition constants measured were Ka, the equilibrium binding constant, and k+2(p), the phosphorylation rate constant. 2. The effects of the alkyl substituents on k+2(p) and k+2(a) were closely parallel, and the decreasing order in each case was: n-butyl; methyl; n-propyl; ethyl. The Taft constants did not follow this order, suggesting that alkyl substituents did not primarily effect acylation or phosphorylation by electron induction. 3. For comparable homologues, the k+2(a) values were on average 435 times the k+2(p) values. The k+2(p) values at 25° and pH7·6 ranged from 6·6min.−1 for the diethyl member to 22·6min.−1 for the di-n-butyl member. 4. The effect of the alkyl substituents on Ka and Km were closely paralleled. The increasing order in each case was: n-butyl; n-propyl; ethyl; methyl. The Ka values were about 100 times less than the comparable Km values. 5. Consideration of the binding energies suggested that only one of the two alkyl groups on the malaoxon homologues bound to the active site. 6. The possibility that malaoxon acted as a substrate as well as an inhibitor for cholinesterase was also investigated, but no evidence of a substrate reaction was found. 相似文献
6.
7.
K Dercová B Vrana Š Baláž A Šándorová 《Journal of industrial microbiology & biotechnology》1996,16(5):325-329
During microbial degradation of PCBs in a liquid medium, two processes influence the PCB concentration in the medium simultaneously: biodegradation and evaporation. The physical loss of PCB due to evaporation frequently causes false positive results in biodegradation experiments. Therefore, if only PCBs are monitored, the determination of the PCB concentration in both liquid and gaseous phases is necessary for a correct appraisal of biodegradation. The kinetics of PCB evaporation and biodegradation were monitored and described by a simple mathematical model. The evaporation and biodegradation rate constants for individual PCB congeners were determined for PCB degradation in liquid medium byPseudomonas stutzeri andAlcaligenes xylosoxidans, both isolated from a longterm PCB-contaminated soil.Symbols
a
1,b
1,a
2,b
2
fitting parameters
-
c
0
initial concentration of PCB congener in liquid medium
-
c
l
concentration of PCB congener in liquid medium
-
c
ev
concentration of PCB congener in sorbent
-
k
ev
rate constant of PCB congener evaporation
-
k
met
rate constant of PCB congener metabolization
-
n
s
amount of PCB congener in sorbent
-
t
1/2
half-time of evaporation
-
V
t
volume of liquid medium 相似文献
8.
M. V. Potapovich A. N. Eryomin I. M. Artzukevich I. P. Chernikevich D. I. Metelitza 《Biochemistry. Biokhimii?a》2001,66(6):646-657
Catalase (CATpp) with molecular weight 223 kD was isolated from the methylotrophic yeast Pichia pastoris and purified 90-fold by ion-exchange chromatography and gel filtration. Quantitative parameters of absorption and CD spectra of CATpp solutions and of its membrane-concentrated form (CATpp-conc) were studied. Rates of H2O2 decomposition and kinetic characteristics K
m and k
cat of CATpp and CATpp-conc were determined in 10 mM phosphate buffer (pH 7.4) at 30°C, as well as the effective constant k
in of the enzyme inactivation rate during the catalysis and the constant k
2 of the interaction rate of the Complex I catalases with H2O2. Thermal inactivation of CATpp in solutions at 45°C was characterized by the effective rate constant k
in
*, and the low-frequency (27 kHz) ultrasonic inactivation of CATpp at 20°C was characterized by the firstorder rate constant k
in (US). All spectral and kinetic characteristics of CATpp and CATpp-conc were compared with the corresponding values for catalase from bovine liver (CAT) and for catalase from the methylotrophic yeast Candida boidinii (CATcb). All three catalases were rather similar in their spectral properties but strongly varied in their kinetic parameters, and their comparison suggests that CATpp should be the best enzyme in its overall properties as it displayed the maximal efficiency in terms of k
cat/K
m, thermal stability comparable with the thermal stability of CAT in terms of k
in
*, the minimal k
in, and high stability in the ultrasonic cavitation field at the US power of 60 W/cm2. 相似文献
9.
M. Ahsanullah 《Biometrical journal. Biometrische Zeitschrift》1982,24(6):559-564
Let {Xn, n≧1} be a sequence of independent and identically distributed random variables. Suppose n(K)=min n for which Xn>Xk, with K fixed and n>K. We will characterize the exponential distribution by considering the distributional properties of Xk and Xk and Xn(k). 相似文献
10.
The water-soluble poly(1-vinyl-2-ethylimidazole) quaternized with ethyl bromide and lauryl bromide was prepared; lauryl group content, 8.8 mol% (L-9), 28.9 mol% (L-29), and 40.9 mol% (L-41). The λmax value of methyl orange near 460 nm shifted to shorter wavelengths (417–433 nm) in the aqueous solution of L-29 and L-41, and the intrinsic viscosity of L-29 was more than ten times smaller than that of L-9. The rate and equilibrium constants (k? and K) for addition of cyanide ion to the N-substituted 3-carboxamidopyridinium ions were studied at 30°C, where N-substituents employed were n-propyl, n-hexyl, benzyl, 2,6-dichlorobenzyl, and n-lauryl. The kinetic parameters for n-lauryl-3-carboxamidopyridinium were markedly increased in the presence of L-29 and L-41 and with increasing polymer concentrations (84-fold for k? and 7800-fold for K), especially at low ionic strength, whereas L-9 decelerated the addition reaction. These distinct behaviors mean that L-29 and L-41 are classified as micellelike polymers and L-9 as a polyelectrolytelike polymer. However, L-29 depressed the rate of the forward reaction for benzyl-3-carboxamidopyridinium, acting like a simple polyelectrolyte. Therefore, the polymer micelle can provide both the microenvironments characteristic of polyelectrolytes and micelles, depending on the hydrophobicity of substrates. 相似文献
11.
Enzyme kinetic studies of inhibition of plant (jackbean) and microbial (Bacillus pasteurii) ureases by eight phosphoroamides [phenylphosphorodiamidate, 4-chlorophenylphosphorodiamidate, phosphoric triamide, N-(diaminophosphinyl)benzamide, N-(diaminophosphinyl)benzeneacetamide, 4-chloro-N-(diaminophosphinyl)benzamide, N-(4-nitrophenyl)phosphoric triamide, N-(diaminophosphinyl)-3-pyridinecarboxamide] demonstrated that these compounds are slow, tight-binding inhibitors of urease enzymes. Measurement of the dissociation constants (Ki*) of the enzyme-inhibitor complexes (E · I*) formed by interaction of the ureases and phosphoroamide inhibitors studied showed that these inhibitors had a much higher affinity (i.e., a lower Ki*) for plant urease than for microbial urease. Measurement of rate constants for formation (kon) and decay (koff) of E · I* showed that, whereas kon varied greatly with the different inhibitors and ureases, koff was constant for the phosphoroamides tested and had a characteristic value for each urease. The half-life of E · I* (30°C; pH 7 THAM buffer) for the plant urease was much longer than that for the microbial urease, and this difference largely accounted for the much higher values of Ki* (koff/kon) observed with microbial urease. 相似文献
12.
A method for preparing various forms of acetylcholinesterase (A ChE) from chicken brain has been developed and they have been characterized in terms of kinetic parameters such as Km, rate constant (k), turnover number (kp), specificity constant (ksp), Vmax and half-life (t1/2). The solubility experiments show that, there are two major forms of A ChE i.e. water-soluble and membrane-bound A ChE (MBA ChE). The MBA ChE shows several subforms, and on the basis of percentage activity only three MBA ChE forms have been selected for complete characterization by various kinetic parameters. It was found that these three forms of MBA ChE demonstrate significant differences in their kinetic properties. 相似文献
13.
Species abundance distributions in neutral models with immigration or mutation and general lifetimes
Amaury Lambert 《Journal of mathematical biology》2011,63(1):57-72
We consider a general, neutral, dynamical model of biodiversity. Individuals have i.i.d. lifetime durations, which are not
necessarily exponentially distributed, and each individual gives birth independently at constant rate λ. Thus, the population size is a homogeneous, binary Crump–Mode–Jagers process (which is not necessarily a Markov process). We assume that types are clonally inherited. We consider two classes of speciation
models in this setting. In the immigration model, new individuals of an entirely new species singly enter the population at constant rate μ (e.g., from the mainland into the island). In the mutation model, each individual independently experiences point mutations in its germ line, at constant rate θ. We are interested in the species abundance distribution, i.e., in the numbers, denoted I
n
(k) in the immigration model and A
n
(k) in the mutation model, of species represented by k individuals, k = 1, 2, . . . , n, when there are n individuals in the total population. In the immigration model, we prove that the numbers (I
t
(k); k ≥ 1) of species represented by k individuals at time t, are independent Poisson variables with parameters as in Fisher’s log-series. When conditioning on the total size of the
population to equal n, this results in species abundance distributions given by Ewens’ sampling formula. In particular, I
n
(k) converges as n → ∞ to a Poisson r.v. with mean γ/k, where γ : = μ/λ. In the mutation model, as n → ∞, we obtain the almost sure convergence of n
−1
A
n
(k) to a nonrandom explicit constant. In the case of a critical, linear birth–death process, this constant is given by Fisher’s
log-series, namely n
−1
A
n
(k) converges to α
k
/k, where α : = λ/(λ + θ). In both models, the abundances of the most abundant species are briefly discussed. 相似文献
14.
The toxic effect of Pb2+ has been studied in eukaryotic cells by using Tetrahymena as a target. The maximum power (P
m) and the growth rate constant (k) were determined, which showed that values of P
m and k were linked to the concentration (C) of Pb2+. The addition of Pb2+ caused a decrease of the maximum heat production and growth rate constant, indicating that Tetrahymena growth was inhibited in the presence of Pb2+, and Pb2+ took part in the metabolism of cells. From micrographs, morphological changes of Tetrahymena were observed with addition of Pb2+, indicating that the toxic effect of Pb2+ derived from destroying the membrane of surface of Tetrahymena. According to the thermogenic curves and photos of Tetrahymena under different conditions, it is clear that metabolic mechanism of Halobacterium halobium R1 growth has been changed with the addition of Pb2+. 相似文献
15.
Shirley M. Norman Stephen M. Poling V. P. Maier Mary D. Nelson 《Bioscience, biotechnology, and biochemistry》2013,77(8):2317-2324
Several compounds having the basic α-ionylideneacetic acid structure were tested in Cercospora rosicola resuspensions. At 100 μm, all the compounds inhibited abscisic acid (ABA) biosynthesis. Time studies with unlabelled and deuterated (2Z,4E)- and (2E,4E)-α-ionylideneacetic acids showed rapid conversions into both (2Z,4E)- and (2E,4E)-4′-keto-α-ionylideneacetic acids as major products. Incorporation of the label into ABA was specific for the 2Z,4E-isomer. Minor products, identified by GC-MS, were (2Z,4E)- and (2E,4E)-4′-hydroxy-α-ionylideneacetic acids and (2Z,4E)-1′-hydroxy-α-ionylideneacetic acid. The conversion to (2Z,4E)-l′-hydroxy-α-ionylideneacetic acid has not been previously reported and was specific for the 2Z,4E-isomer. A time study for the conversion of methyl esters of [2H3]-(2Z,4E)- and [2H3]-(2E,4E)-4′-keto-α-ionylideneacetates showed a slow introduction of the l′-hydroxyl group and specificity for 2Z,4E-isomer. Conversion of the ethyl esters of (2Z,4E)- and (2E,4E)-l′-hydroxy-α-ionylideneacetates into the ethyl esters of both ABA and (2E,4E)-ABA demonstrated that ABA can be formed by oxidation of the 4′-position after the insertion of the 1′-hydroxy group. The ethyl 1′-hydroxy acids were also isomerized to the corresponding ethyl (2Z,4E)- and ethyl (2E,4E)-3′-hydroxy-β-ionylideneacetates. Ethyl (2Z,4E)-1′-hydroxy acid also gave small amounts of ethyl l′,4′-trans-diol of ABA. These results suggest that ABA may be formed through a (2Z,4E)-1′-hydroxy-α-ionylidene-type intermediate in addition to the previously proposed route through (2Z,4E)-4′-keto-α-ionylideneacetic acid. 相似文献
16.
The pre-steady states of Pseudomonas species lipase inhibitions by p-nitrophenyl-N-substituted carbamates (1–6) are composed of two steps: (1) formation of the non-covalent enzyme–inhibitor complex (E:I) from the inhibitor and the enzyme
and (2) formation of the tetrahedral enzyme–inhibitor adduct (E–I) from the E:I complex. From a stopped-flow apparatus, the
dissociation constant for the E:I complex, KS, and the rate constant for formation of the tetrahedral E–I adduct from the E:I complex, k2 are obtained from the non-linear least-squares of curve fittings of first-order rate constant (kobs) versus inhibition concentration ([I]) plot against kobs=k2+k2[I]/(KS+[I]). Values of pKS, and log k2 are linearly correlated with the σ* values with the ρ* values of −2.0 and 0.36, respectively. Therefore, the E:I complexes are more positive charges than the inhibitors due to
the ρ* value of −2.0. The tetrahedral E–I adducts on the other hand are more negative charges than the E:I complexes due to the
ρ* value of 0.36. Formation of the E:I complex from the inhibitor and the enzyme are further divided into two steps: (1) the
pre-equilibrium protonation of the inhibitor and (2) formation of the E:I complex from the protonated inhibitor and the enzyme. 相似文献
17.
Wenmin Chen Peng Zhan Erik De Clercq Christophe Pannecouque Jan Balzarini Xin Jiang Xinyong Liu 《Bioorganic & medicinal chemistry》2013,21(22):7091-7100
A series of N2,N4-disubstituted-1,1,3-trioxo-2H,4H-pyrrolo[1,2-b][1,2,4,6]thiatriazine derivatives (PTTDs) was designed and synthesized by a facile route. The biological assay results showed that five most potent compounds displayed inhibitory activity against HIV-1 at low micromolar concentrations (EC50 = 5.1–8.9 μM). Structure–activity relationship analysis indicated that N2-(3-halogenated-benzyl) analogues were more potent than N2-(unsubstituted-benzyl) analogues. The N4-substitutions contributed to the antiviral activity in the following order: 2-/3-cyano substituted benzyl > 2-/3-halogenated benzyl > non-substituted benzyl > 4-halogenated benzyl. Docking studies of the representative compound revealed the binding conformation of these compounds and provided critical insights for the further development of PTTD analogues. 相似文献
18.
The toxicity to adults of the American house dust mite, Dermatophagoides farinae, and the European house dust mite, Dermatophagoides pteronyssinus, of cassia bark and cassia and cinnamon oil compounds was examined using residual contact and vapour-phase toxicity bioassays.
Results were compared with those of the currently used acaricides: benzyl benzoate and dibutyl phthalate. The acaricidal principles
of cassia bark were identified as (E)-cinnamaldehyde and salicylaldehyde. In fabric-circle residual contact bioassays with adult D. farinae, salicylaldehyde (17.3 mg/m2) and (E)-cinnamaldehyde (25.8 mg/m2) were 2.5 and 1.7 times more toxic than benzyl benzoate (43.7 mg/m2), respectively, based on 24-h LD50 values. The acaricidal activity was more pronounced in benzaldehyde, menthol, α-terpineol, and thymol (70.8–234.3 mg/m2) than in dibutyl phthalate (281.0 mg/m2). Against adult D. pteronyssinus, salicylaldehyde (17.3 mg/m2) and (E)-cinnamaldehyde (19.3 mg/m2) were 2.4- and 2.2-fold more active than benzyl benzoate (41.9 mg/m2). The toxicity of benzaldehyde, menthol, α-terpineol, and thymol (75.3–179.2 mg/m2) was higher than that of dibutyl phthalate (285.1 mg/m2). In vapour-phase toxicity tests with adult D. farinae, the test compounds described were much more effective in closed—but not in open—containers, indicating that the effect of
these compounds was largely a result of action in the vapour phase. 相似文献
19.
Madhubhashini Makehelwala K. B. S. N. Jinadasa Norio Tanaka Rohan Weerasoriya Athula Bandara 《Bioremediation Journal》2009,13(4):188-197
Reductive adsorption of Cr(VI) on coir pith (hereafter CP) was examined as a function of pH, ionic strength, and temperature. The CP contains 1.33 meq g? 1 phenolic, 0.43 meq g? 1 of lactonic, and 0.35 meq g? 1 carboxylic sites. Thus the CP surface is enriched with electron-donating oxygen functionalities. As evidenced by infrared (IR) spectroscopy, the Cr(VI) → Cr(III) conversion is facilitated by CP sites that are enriched with O─ O functional groups. The adsorption of reduced Cr(VI) was found to occur via C─ O─ functional groups first forming innersphere complexes with the CP surface, yielding keto (> C═ O) groups on the CP surface. The reductive adsorption of Cr(VI) was almost completed within 3 to 4 h, and it was dependent on pH and background ionic strength, yielding the highest monolayer coverage (9.56E-7 mol m? 2) at pH 3.7 in 0.1 M NaNO3. The ΓCr(III) followed the order with respect to the ionic strength: Γ0.1 M > Γ0.01 M > Γ0.001 M. The initial rate constant, k i , increased with temperature as k i 313 K > k i 303 K > k i 293 K > k i 283 K. 相似文献
20.
da Silva TL Mendes A Mendes RL Calado V Alves SS Vasconcelos JM Reis A 《Journal of industrial microbiology & biotechnology》2006,33(6):408-416
The potential use of n-dodecane as an oxygen vector for enhancement of Crypthecodinium cohnii growth and docosahexaenoic acid (DHA) production was studied. The volumetric fraction of oxygen vector influenced the gas–liquid volumetric mass transfer coefficient k
L
a positively. The k
L
a increased almost linearly with the increase of volumetric fraction of n-dodecane up to 1%. The stirring rate showed a higher influence on the k
L
a than the aeration rate. The effects of this hydrocarbon on C. cohnii growth and DHA production were then investigated. A control batch fermentation without n-dodecane addition (CF) and a batch fermentation where n-dodecane 1% (v/v) was added (DF) were carried out simultaneously under the same experimental conditions. It was found that, before 86.7 h of fermentation, the biomass concentration, the specific growth rate, the DHA, and total fatty acids (TFA) production were higher in the CF. After this fermentation time, the biomass concentration, the DHA and TFA production were higher in the DF. The highest DHA content of biomass (6.14%), DHA percentage of TFA (51%), and DHA production volumetric rate r
DHA (9.75 mg l−1 h−1) were obtained at the end of the fermentation with n-dodecane (135.2 h). The dissolved oxygen tension (DOT) was always higher in the DF, indicating a better oxygen transfer due to the oxygen vector presence. However, since the other C. cohnii unsaturated fatty acids percentages did not increase with the oxygen availability increase due to the n-dodecane presence, a desaturase oxygen-dependent mechanism involved in the C. cohnii DHA biosynthesis was not considered to explain the DHA production increase. A selective extraction through the n-dodecane was suggested. 相似文献