共查询到20条相似文献,搜索用时 31 毫秒
1.
The integrated forms of the Michaelis-Menten equation assuming variable substrate (depletion) or constant substrate concentration
were used to study the effect of the simultaneous presence of two exoglucanase Cel7A inhibitors (cellobiose and ethanol) on
the kinetics of cellulose hydrolysis. The kinetic parameters obtained, assuming constant substrate (K
m
=21 mM, K
ic
=0.035 mM; K
icl
=1.5×1015mM; k
cat=12 h−1) or assuming variable substrate (K
m
=16 mM, K
ic
=0.037 mM; K
icl
=5.8×1014 mM; k
cat=9 h−1), showed a good similarity between these two alternative methodologies and pointed out that bothethanol and cellobiose are
competitive inhibitors. Nevertheless, ethanol is a very weak inhibitor, as shown by the large value estimated for the kinetic
constant K
icl
. In addition, assuming different concentrations of initial accessible substrate present in the reaction, both inhibition
and velocity constants are at the same order of magnitude, which is consistent with the obtained values. The possibility of
using this kind of methodology to determine kinetic constants in general kinetic studies is discussed, and several integrated
equations of different Michaelis-Menten kinetic models are presented. Also examined is the possibility of determining inhibition
constants without knowledge of the true accessible substrate concentration. 相似文献
2.
Chromium(III)-lutidinato complexes of general formula [Cr(lutH)
n
(H2O)6−2n
]3−n (where lutH− is N,O-bonded lutidinic acid anion) were obtained and characterized in solution. Acid-catalysed aquation of [Cr(lutH)3]0 leads to only one ligand dissociation, whereas base hydrolysis produces chromates(III) as a result of subsequent ligand liberation
steps. The kinetics of the first ligand dissociation were studied spectrophotometrically, within the 0.1–1.0 M HClO4 and 0.4–1.0 M NaOH range. In acidic media, two reaction stages, the chelate-ring opening and the ligand dissociation, were
characterized. The dependencies of pseudo-first-order rate constants on [H+] are as follows: k
obs1 = k
1 + k
−1/K
1[H+] and k
obs2 = k
2
K
2[H+]/(1 + K
2[H+]), where k
1 and k
2 are the rate constants for the chelate-ring opening and the ligand dissociation, respectively, k
−1 is the rate constant for the chelate-ring closure, and K
1 and K
2 are the protonation constants of the pyridine nitrogen atom and coordinated 2-carboxylate group in the one-end bonded intermediate,
respectively. In alkaline media, the rate constant for the first ligand dissociation depends on [OH−]: k
obs1 = k
OH(1) + k
O[OH−], where k
OH(1) and k
O are rate constants of the first ligand liberation from the hydroxo- and oxo-forms of the intermediate, respectively, and
K
2 is an equilibrium constant between these two protolytic forms. Kinetic parameters were determined and a mechanism for the
first ligand dissociation is proposed. The kinetics of the ligand liberation from [Cr(lut)(OH)4]3− were also studied and the values of the pseudo-first-order rate constants are [OH−] independent. 相似文献
3.
Javed MR Rashid MH Nadeem H Riaz M Perveen R 《Applied biochemistry and biotechnology》2009,157(3):483-497
Monomeric extracellular endoglucanase (25 kDa) of transgenic koji (Aspergillus oryzae cmc-1) produced under submerged growth condition (7.5 U mg−1 protein) was purified to homogeneity level by ammonium sulfate precipitation and various column chromatography on fast protein
liquid chromatography system. Activation energy for carboxymethylcellulose (CMC) hydrolysis was 3.32 kJ mol−1 at optimum temperature (55 °C), and its temperature quotient (Q
10) was 1.0. The enzyme was stable over a pH range of 4.1–5.3 and gave maximum activity at pH 4.4. V
max for CMC hydrolysis was 854 U mg−1 protein and K
m was 20 mg CMC ml−1. The turnover (k
cat) was 356 s−1. The pK
a1 and pK
a2 of ionisable groups of active site controlling V
max were 3.9 and 6.25, respectively. Thermodynamic parameters for CMC hydrolysis were as follows: ΔH* = 0.59 kJ mol−1, ΔG* = 64.57 kJ mol−1 and ΔS* = −195.05 J mol−1 K−1, respectively. Activation energy for irreversible inactivation ‘E
a(d)’ of the endoglucanase was 378 kJ mol−1, whereas enthalpy (ΔH*), Gibbs free energy (ΔG*) and entropy (ΔS*) of activation at 44 °C were 375.36 kJ mol−1, 111.36 kJ mol−1 and 833.06 J mol−1 K−1, respectively. 相似文献
4.
5.
A laccase has been purified from the liquid culture growth medium containing bagasse particles of Fomes durissimus. The method involved concentration of the culture filtrate by ultrafiltration and anion exchange chromatography on diethyl
aminoethyl cellulose. The sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE) and native polyacrylamide
gel electrophoresis both gave single protein band indicating that the enzyme preparation was pure. The molecular mass of the
purified laccase determined from SDS-PAGE analysis was 75 kDa. Using 2,6-dimethoxyphenol as the substrate, the determined
K
m and k
cat values of the laccase are 182 μM and 0.35 s−1, respectively, giving a k
cat/K
m value of 1.92 × 103 M−1 s−1. The pH and temperature optimum were 4.0 and 35 °C, respectively. The purified laccase has yellow colour and does not show
absorption band around 610 nm found in blue laccases. Moreover, it transformed methylbenzene to benzaldehyde in the absence
of mediator molecules, property exhibited by yellow laccases. 相似文献
6.
Bruno Benoliel Marcio José Poças-Fonseca Fernando Araripe Gonçalves Torres Lidia Maria Pepe de Moraes 《Applied biochemistry and biotechnology》2010,160(7):2036-2044
A β-glucosidase gene (bgl4) from Humicola grisea var thermoidea was successfully expressed in Saccharomyces cerevisiae. The recombinant protein (BGL4
Sc
) was initially detected associated with yeast cells and later in the culture medium. BGL4
Sc
showed optimal pH and temperature of 6.0 and 40 °C, respectively, and an apparent molecular mass of 57 kDa. The enzyme showed
activity against cellobiose and synthetic substrates, and was inhibited more than 80% by Fe2+, Cu2+, Zn2+, and Al3+. Using p-nitrophenyl-β-d-glucopyranoside (pNPG) as substrate, BGL4
Sc
presented a V
max of 6.72 μmol min−1 mg total protein−1 and a K
m of 0.16 mM under optimal conditions. Most important, BGL4
Sc
is resistant to inhibition by glucose and the calculated K
i value for this sugar is 70 mM. This feature prompts BLG4
Sc
as an ideal enzyme to be used in the saccharification process of lignocellulosic materials for ethanol production. 相似文献
7.
Oxidation of N-methylethylamine by bis(hydrogenperiodato)argentate(III) ([Ag(HIO6)2]5−) in alkaline medium results in demethylation, giving rise to formaldehyde and ethylamine as the oxidation products. The oxidation
kinetics has been followed spectrophotometrically in the temperature range of 20.0–35.0 °C, and shows an overall second-order
character: being first-order with respect to both Ag(III) and N-methylethylamine. The observed second-order rate constants k′ increase with increasing [OH−] of the reaction medium, but decrease with increasing the total concentration of periodate. An empirical rate expression
for k′ has been derived as: k′ = (k
a + k
b[OH−])K
1/{f([OH−])[IO4
−]tot + K
1}, where k
a and k
b are rate parameters, and K
1 is an equilibrium constant. These parameters have been evaluated at all the temperatures studied, enabling calculation of
activation parameters. A reaction mechanism is suggested to involve two pre-equilibria, leading to formation of an intermediate
Ag(III) complex, namely [Ag(HIO6)(OH)(MeNHEt)]2−. In the subsequent rate-determining steps, this intermediate undergoes inner-sphere electron transfer from the coordinated
amine to the metal center via two distinct routes, one of which is spontaneous while the other is mediated by a hydroxide
ion. 相似文献
8.
Hossein Amani Mohammad Reza Mehrnia Mohammad Hossein Sarrafzadeh Manouchehr Haghighi Mohammad Reza Soudi 《Applied biochemistry and biotechnology》2010,162(2):510-523
There is a lack of fundamental knowledge about the scale up of biosurfactant production. In order to develop suitable technology
of commercialization, carrying out tests in shake flasks and bioreactors was essential. A reactor with integrated foam collector
was designed for biosurfactant production using Bacillus subtilis isolated from agricultural soil. The yield of biosurfactant on biomass (Y
p/x), biosurfactant on sucrose (Y
p/s), and the volumetric production rate (Y) for shake flask were obtained about 0.45 g g−1, 0.18 g g−1, and 0.03 g l−1 h−1, respectively. The best condition for bioreactor was 300 rpm and 1.5 vvm, giving Y
x/s, Y
p/x, Y
p/s, and Y of 0.42 g g−1, 0.595 g g−1, 0.25 g g−1, and 0.057 g l−1 h−1, respectively. The biosurfactant maximum production, 2.5 g l−1, was reached in 44 h of growth, which was 28% better than the shake flask. The obtained volumetric oxygen transfer coefficient
(K
L
a) values at optimum conditions in the shake flask and the bioreactor were found to be around 0.01 and 0.0117 s−1, respectively. Comparison of K
L
a values at optimum conditions shows that biosurfactant production scaling up from shake flask to bioreactor can be done with
K
L
a as scale up criterion very accurately. Nearly 8% of original oil in place was recovered using this biosurfactant after water
flooding in the sand pack. 相似文献
9.
Hassan A. Ewais 《Transition Metal Chemistry》2009,34(5):539-547
The oxidation of [CoII(nta)(ox)(H2O)2]3− and [CoII(nta)(ph)(H2O)2]3− (nta = nitrilotriacetate, ox = oxalic acid and ph = phthalic acid) by periodate have been studied kinetically in aqueous
solution over 20–40 °C and a variety of pH ranges. The rate of oxidation of [CoII(nta)(ox)(H2O)2]3− by periodate, obeys the following equation: d[CoIII]/dt = [CoII(nta)(ox)(H2O)23−][H5IO6] {k
4
K
5 + (k
5
K
6
K
2/[H+]} while the reaction of [CoII(nta)(ph)(H2O)2]3− with periodate in aqueous acidic medium obeys the following rate law: d[CoIII]/dt = k
6
K
8[CoII]T [IVII]T/{1 + [H+]/K
7 + K
8[IVII]
T
}. Initial cobalt(III) products were formed and slowly converted to final products, fitting an inner-sphere mechanism. Thermodynamic
activation parameters have been calculated. A common mechanism for the oxidation of ternary nitrilotriacetatocobalt(II) complexes
by periodate is proposed and supported by an excellent isokinetic relationship between ΔH* and ΔS* values for these reactions. 相似文献
10.
Hongmei Shi Shipeng Liu Shigang Shen Shuying Huo Weijun Kang 《Transition Metal Chemistry》2009,34(8):821-826
Kinetics of oxidation of dl-pipecolinate by bis(hydrogenperiodato)argentate(III) complex anion, [Ag(HIO6)2]5−, has been studied in aqueous alkaline medium in the temperature range of 25–40 °C. The oxidation kinetics is first order
in the silver(III) and pipecolinate concentrations. The observed second-order rate constant, decreasing with increasing [periodate]
is virtually independent of [OH−]. α-Aminoadipate as the major oxidation product of pipecolinate has been identified by chromatographic analysis. A reaction
mechanism is proposed that involves a pre-equilibrium between [Ag(HIO6)2]5− and [Ag(HIO6)(H2O)(OH)]2−, a mono-periodate coordinated silver(III) complex. Both Ag(III) complexes are reduced in parallel by pipecolinate in rate-determining
steps (described by k
1 for the former Ag(III) species and k
2 for the latter). The determined rate constants and their associated activation parameters are k
1 (25 °C) = 0.40 ± 0.02 M−1 s−1, ∆H
1≠ = 53 ± 2 kJ mol−1, ∆S
1≠ = −74 ± 5 J K−1 mol−1 and k
2 (25 °C) = 0.64 ± 0.02 M−1 s−1, ∆H
2≠ = 41 ± 2 kJ mol−1, ∆S
2≠ = −110 ± 5 J K−1 mol−1. The time-resolved spectra, a positive dependence of the rate constants on ionic strength of the reaction medium, and the
consistency of pre-equilibrium constants derived from different reaction systems support the proposed reaction mechanism. 相似文献
11.
Yanna Liang Zisong Feng Jemil Yesuf James W. Blackburn 《Applied biochemistry and biotechnology》2010,160(6):1841-1852
A newly isolated Anoxybacillus sp. 527 was found to grow on crystalline cellulose as sole carbon and energy sources. Cellulases secreted by strain 527 were
better induced by cellobiose, followed by glucose, lactose, sucrose, and cellulose. Cellulase secretion was enhanced by an
optimized medium. Cellulase activity was increased by the addition of Ca2+ and NH4+ and achieved maximum as 7.0 FPU ml−1 at 70 °C and pH 6.0. Even at 100 °C, the enzymes were still active, which implies their potential application in large-scale
cellulose conversion process. 相似文献
12.
The ethanol effect on the Trichoderma reesei cellulases was studied to quantify and clarify this inhibition type. To determine inhibition parameters of crude cellulase
and purified exoglucanase Cel7A, integrated Michaelis-Menten equations were used assuming the presence of two inhibitors:
cellobiose as the reaction product and ethanol as a possible bioproduct of cellulose fermentation.
It was found that hydrolysis of cellulose by crude enzyme follows a model that considers noncompetitive inhibition by ethanol,
whereas Cel7A is very slightly competitively inhibited. Crude cellulase is much more inhibited (K
iul=K
icl=151.9 mM) than exoglucanase Cel7A (K
icl=1.6 × 1015 mM). Also, calculated inhibition constants showed that cellobiose inhibition is more potent than ethanol inhibition both for
the crude enzyme as well as exoglucanase Cel7A. 相似文献
13.
Jingjing Yu Jiaxing Tu Faqiong Zhao Baizhao Zeng 《Journal of Solid State Electrochemistry》2010,14(9):1595-1600
A magnetic mesoporous carbon material (i.e., mesoporous iron oxide/C, mesoFe/C) is synthesized for protein immobilization,
using glucose oxidase (GOx) as model. Transmission electron microscopy images show that mesoFe/C has highly ordered porous
structure with uniform pore size, and iron oxide nanoparticles are dispersed along the wall of carbon. After adsorption of
GOx, the GOx-mesoFe/C composite is separated with magnet. The immobilized GOx remains its natural structure according to the
reflection–absorption infrared spectra. When the GOx-mesoFe/C composite is coated on a Pt electrode surface, the GOx gives
a couple of quasireversible voltammetric peaks at −0.5 V (vs. saturated calomel electrode) due to the redox of FAD/FADH2. The electron-transfer rate constant (k
s) is ca. 0.49 s−1. The modified electrode presents remarkably amperometric response to glucose at 0.6 V. The response time (t
95%) is less than 6 s; the response current is linear to glucose concentration in the range of 0.2–10 mM with a sensitivity of
27 μA mM−1 cm−2. The detection limit is 0.08 mM (S/N = 3). The apparent Michaelis–Menten constant (K
mapp) of the enzyme reaction is ca. 6.6 mM, indicating that the GOx immobilized with mesoFe/C has high affinity to the substrate. 相似文献
14.
The kinetics of oxidation of phenyldiethanolamine (PEA) by a silver(III) complex anion, [Ag(HIO6)2]5−, has been studied in an aqueous alkaline medium by conventional spectrophotometry. The main oxidation product of PEA has
been identified as formaldehyde. In the temperature range 20.0–40.0 °C , through analyzing influences of [OH−] and [IO
4
−
]tot on the reaction, it is pseudo-first-order in Ag(III) disappearance with a rate expression: k
obsd = (k
1 + k
2[OH−]) K
1
K
2[PEA]/{f([OH−])[IO
4
−
]tot + K
1 + K
1
K
2 [PEA]}, where k
1 = (0.61 ± 0.02) × 10−2 s−1, k2 = (0.049 ± 0.002) M−1 s−1 at 25.0 °C and ionic strength of 0.30 M. Activation parameters associated with k
1 and k
2 have also been derived. A reaction mechanism is proposed involving two pre-equilibria, leading to formation of an Ag(III)-periodato-PEA
ternary complex. The ternary complex undergoes a two-electron transfer from the coordination PEA to the metal center via two
parallel pathways: one pathway is spontaneous and the other is assisted by a hydroxide ion. 相似文献
15.
Marcelo H. Gehlen 《Cellulose (London, England)》2009,16(6):1069-1073
Depolymerization of cellulose in homogeneous acidic medium is analyzed on the basis of autocatalytic model of hydrolysis with
a positive feedback of acid production from the degraded biopolymer. The normalized number of scissions per cellulose chain,
S(t)/n° = 1 − C(t)/C0, follows a sigmoid behavior with reaction time t, and the cellulose concentration C(t) decreases exponentially with a linear and cubic time dependence, C(t) = C0exp[−at − bt
3], where a and b are model parameters easier determined from data analysis. 相似文献
16.
Rodrigues TH Rocha MV de Macedo GR Gonçalves LR 《Applied biochemistry and biotechnology》2011,164(6):929-943
In this work, the potential of microwave-assisted alkali pretreatment in order to improve the rupture of the recalcitrant
structures of the cashew able bagasse (CAB), lignocellulosic by-product in Brazil with no commercial value, is obtained from
cashew apple process to juice production, was studied. First, biomass composition of CAB was determined, and the percentage
of glucan and lignin was 20.54 ± 0.70% and 33.80 ± 1.30%, respectively. CAB content in terms of cellulose, hemicelluloses,
and lignin, 19.21 ± 0.35%, 12.05 ± 0.37%, and 38.11 ± 0.08%, respectively, was also determined. Results showed that, after
enzymatic hydrolysis, alkali concentration exerted influence on glucose formation, after pretreatment with 0.2 and 1.0 mo L−1 of NaOH (372 ± 12 and 355 ± 37 mg gglucan−1) when 2% (w/v) of cashew apple bagasse pretreated by microwave-assisted alkali pretreatment (CAB-M) was used. On the other hand, pretreatment
time (15–30 min) and microwave power (600–900 W) exerted no significant effect on hydrolysis. On enzymatic hydrolysis step,
improvement on solid percentage (16% w/v) and enzyme load (30 FPU gCAB-M−1) increased glucose concentration to 15 g L−1. The fermentation of the hydrolyzate by Saccharomyces cerevesiae resulted in ethanol concentration and productivity of 5.6 g L−1 and 1.41 g L−1 h−1, respectively. 相似文献
17.
Hye-Jung Kim Sueng Yeun Kang Jong Jin Park Pil Kim 《Applied biochemistry and biotechnology》2011,163(3):444-451
Uridine diphosphogalactose-4-epimerase (UDP-galactose-4-epimerase, GalE, EC 5.1.3.2) mediates the 4-epimerization of nucleic
acid-activated galactose into UDP-glucose. To date, no enzyme is known to mediate 4-epimerization of free monosaccharide substrates.
To determine the potential activity of GalE for free monosaccharide, Escherichia coli GalE was expressed and purified using Ni-affinity chromatography, and its ability to mediate 4-epimerization of a variety
of free keto- and aldohexoses was assessed. Purified GalE was found to possess 4-epimerization activity for free galactose,
glucose, fructose, tagatose, psicose, and sorbose at 0.47, 0.31, 2.82, 9.67, 15.44, and 2.08 nmol/mg protein per minute, respectively.
No 4-epimerization activity was found for allose, gulose, altrose, idose, mannose, and talose. The kinetic parameters of 4-epimerization
reactions were K
m = 26.4 mM and k
cat = 0.0155 min−1 for d-galactose and K
m = 237 mM and k
cat = 0.327 min−1 for d-tagatose. The 4-epimerization of tagatose, a reaction of commercial interest, was enhanced twofold (19.79 nmol/mg protein
per minute) when asparagine was exchanged with serine at position 179. The novel activity of GalE for free monosaccharide
may be beneficial for the production of rare sugars using cheap natural resources. Potential strategies for developing enhanced
GalE with increased 4-epimerization activity are discussed in the context of the above findings and an analysis of a 3D structural
model. 相似文献
18.
Summary The kinetics of the acid-catalysed hydrolysis of the [(imidazole)4Co(CO3)]+ ion was found to follow the rate law -dln[complex]/dt = k
1
K[H+](1 + K[H
+]) in the 25–45 °C range, [H+] 0.05–1.0 m range and I = 1.0m. The reaction sequence consists of a rapid protonation equilibrium followed by the one-end dissociation of the coordinated
carbonato ligand (rate-determining step) and subsequent fast release of the monodentate carbonato ligand. The rate parameter
values, k
1 and ITK, at 25 °C are 6.48 × 10−3s−1 and 0.31m
−1, respectively, and activation parameters for k
1 are ΔH
1
≠ = 86.1 ± 1.2kJ mol−1 and ΔS
1
≠ = 2.1 ± 6.3 J mol−1K−1. The hydrolysis rate increases with increase in ionic strength. The different ways of dealing with the data fit are presented
and discussed. The kinetic results are compared with those for the similar cobalt(III) complexes. 相似文献
19.
Peroxydisulfate (PDS) oxidizes N,N′-ethylenebis(isonitrosoacetyleacetoneimine)copper(II) complex, CuIIL, to the corresponding copper(III) complex, [CuIIIL]+. The kinetic runs were performed in the presence of EDTA to scavenge any trace metal impurities. The kinetics of the reaction
at constant pH, ionic strength, and temperature obeys the rate law d[CuIIIL]/dt = 2k
2[CuIIL][S2O8
2−] with k
2 having a value of (8.85 ± 0.32) × 10−2 M−1 s−1 at μ = 0.30 M and T = 25.0 °C. The rate constant k
2 is not affected by variation of pH over the range 3.60–5.20. The second order rate constant is also unaffected by changing
ionic strength. The values of k
obs were determined over the temperature 25.0–40.0 °C range. The enthalpy of activation, ∆H*, and entropy of activation, ∆S*, have been calculated as 34.9 ± 0.5 kJ mol−1 and −173.3 ± 11.4 J K−1 mol−1, respectively. The kinetics of this reaction, as far as we know, is the first evidence that copper(III) is the likely reactive
species in copper catalyzed PDS oxidation reactions. 相似文献
20.
M. López-Sánchez M. J. Ayora-Cañada A. Molina-Díaz M. Siam W. Huber G. Quintás S. Armenta B. Lendl 《Analytical and bioanalytical chemistry》2009,394(8):2137-2144
A mid-infrared enzymatic assay for label-free monitoring of the enzymatic reaction of fructose-1,6-bisphosphatase with fructose
1,6-bisphosphate has been proposed. The whole procedure was done in an automated way operating in the stopped flow mode by
incorporating a temperature-controlled flow cell in a sequential injection manifold. Fourier transform infrared difference
spectra were evaluated for kinetic parameters, like the Michaelis–Menten constant (K
M) of the enzyme and V
max of the reaction. The obtained K
M of the reaction was 14 ± 3 g L−1 (41 μM). Furthermore, inhibition by adenosine 5′-monophosphate (AMP) was evaluated, and the K
MApp value was determined to be 12 ± 2 g L−1 (35 μM) for 7.5 and 15 μM AMP, respectively, with V
max decreasing from 0.1 ± 0.03 to 0.05 ± 0.01 g L−1 min−1. Therefore, AMP exerted a non-competitive inhibition. 相似文献