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1.
Xu Z Li S Fu F Li G Feng X Xu H Ouyang P 《Applied biochemistry and biotechnology》2012,166(4):961-973
d-tagatose is a ketohexose that can be used as a novel functional sweetener in foods, beverages, and dietary supplements. This
study was aimed at developing a high-yielding d-tagatose production process using alginate immobilized Lactobacillus fermentum CGMCC2921 cells. For the isomerization from d-galactose into d-tagatose, the immobilized cells showed optimum temperature and pH at 65 °C and 6.5, respectively. The alginate beads exhibited
a good stability after glutaraldehyde treatment and retained 90% of the enzyme activity after eight cycles (192 h at 65 °C)
of batch conversion. The addition of borate with a molar ratio of 1.0 to d-galactose led to a significant enhancement in the d-tagatose yield. Using commercial β-galactosidase and immobilized L. fermentum cells, d-tagatose was successfully obtained from lactose after a two-step biotransformation. The relatively high conversion rate and
productivity from d-galactose to d-tagatose of 60% and 11.1 g l−1 h−1 were achieved in a packed-bed bioreactor. Moreover, lactobacilli have been approved as generally recognized as safe organisms,
which makes this L. fermentum strain an attracting substitute for recombinant Escherichia coli cells among d-tagatose production progresses. 相似文献
2.
I. E. Paukov Yulia A. Kovalevskaya Elena V. Boldyreva 《Journal of Thermal Analysis and Calorimetry》2010,100(1):295-301
Heat capacity C
p(T) of the crystalline dl-cysteine was measured on heating the system from 6 to 309 K by adiabatic calorimetry; thermodynamic functions were calculated
based on these data smoothed in the temperature range 6–273.15 K. The values of heat capacity, entropy, and enthalpy at 273.15 K
were equal to 142.4, 153.3, and 213.80 J K−1 mol−1, respectively. At about 300 K, a heat capacity peak was observed, which was interpreted as an evidence of a first-order phase
transition. The enthalpy and the entropy of the transition are equal, respectively, to 2300 ± 50 and 7.6 ± 0.1 J K−1 mol−1. 相似文献
3.
Parnajyoti Karmakar Subhasis Mallick Biplab K. Bera Arup Mandal Subala Mondal Sudip K. Mukhopadhyay Alak K. Ghosh 《Transition Metal Chemistry》2010,35(8):911-916
The kinetics of the interaction of glycine-l-leucine (Glyleu) with cis-[Pt(cis-dach)(OH2)2]2+ (dach = 1,2-diaminocyclohexane) has been studied spectrophotometrically as a function of [cis-[Pt(cis-dach)(OH2)2]2+], [Glyleu] and temperature at pH 4.0, where the complex exists predominantly as the diaqua species and Glyleu as a zwitterion.
The substitution reaction shows two consecutive steps: the first is the ligand-assisted anation and the second is the chelation
step. The activation parameters for both the steps were evaluated using Eyring’s equation. The low ∆H1≠ (51.9 ± 2.8 kJmol−1) and large negative value of ∆S1≠ (−152 ± 8 JK−1mol−1) as well as ∆H2≠ (54.4 ± 1.7 kJmol−1) and ∆S2≠ (−162 ± 5 JK−1mol−1) indicate an associative mode of activation for both the aqua ligand substitution processes. 相似文献
4.
To express high-active soluble d-amino acid oxidase (DAAO), a constitutive plasmid that is regulated by a native hydantoinase promoter (PHase), was constructed. A d-amino acid oxidase gene (dao) was ligated with the PHase and cloned into pGEMKT to constitutively express protein of DAAO without the use of any inducer such as isopropyl β-d-1-thiogalactopyranoside which is poisonous to the cells and environment. The ribosome binding site region, host strain, and
fermentation conditions were optimized to increase the expression level. When cultivated in a 5-m3 fermenter, the enzyme activity of JM105/pGEMKT-R-DAAO grown at 37 °C was found to be 32 U/mL and increase 16-fold over cells
of BL21(DE3)/pET-DAAO grown at 28 °C. These results indicate the success of our approaches to overproducing DAAO in soluble
form in Escherichia coli. 相似文献
5.
A 66-kDa thermostable family 1 Glycosyl Hydrolase (GH1) enzyme with β-glucosidase and β-galactosidase activities was purified
to homogeneity from the seeds of Putranjiva roxburghii belonging to Euphorbiaceae family. N-terminal and partial internal amino acid sequences showed significant resemblance to plant GH1 enzymes. Kinetic
studies showed that enzyme hydrolyzed p-nitrophenyl β-d-glucopyranoside (pNP-Glc) with higher efficiency (K
cat/K
m = 2.27 × 104 M−1 s−1) as compared to p-nitrophenyl β-d-galactopyranoside (pNP-Gal; K
cat/K
m = 1.15 × 104 M−1 s−1). The optimum pH for β-galactosidase activity was 4.8 and 4.4 in citrate phosphate and acetate buffers respectively, while
for β-glucosidase it was 4.6 in both buffers. The activation energy was found to be 10.6 kcal/mol in the temperature range
30–65 °C. The enzyme showed maximum activity at 65 °C with half life of ~40 min and first-order rate constant of 0.0172 min−1. Far-UV CD spectra of enzyme exhibited α, β pattern at room temperature at pH 8.0. This thermostable enzyme with dual specificity
and higher catalytic efficiency can be utilized for different commercial applications. 相似文献
6.
Meijuan Xu Zhiming Rao Hong Xu Chunyan Lan Wenfang Dou Xiaomei Zhang Hongyu Xu Jian Jin Zhenghong Xu 《Applied biochemistry and biotechnology》2011,163(6):707-719
Corynebacterium crenatum SYPA 5-5 is an aerobic and industrial l-arginine producer. It was proved that the Corynebacterium glutamicum/Escherichia coli shuttle vector pJC1 could be extended in C. crenatum efficiently when using the chloramphenicol acetyltransferase gene (cat) as a reporter under the control of promoter tac. The expression system was applied to over-express the gene vgb coding Vitreoscilla hemoglobin (VHb) to further increase the dissolved oxygen in C. crenatum. As a result, the recombinant C. crenatum containing the pJC-tac-vgb plasmid expressed VHb at a level of 3.4 nmol g−1, and the oxygen uptake rates reached 0.25 mg A562−1 h−1 which enhanced 38.8% compared to the wild-type strain. Thus, the final l-arginine concentration of the batch fermentation reached a high level of 35.9 g L−1, and the biomass was largely increased to 6.45 g L−1, which were 17.3% and 10.5% higher than those obtained by the wild-type strain, respectively. To our knowledge, this is the
first report that the efficient expression system was constructed to introduce vgb gene increasing the oxygen and energy supply for l-arginine production in C. crenatum, which supplies a good strategy for the improvement of amino acid products. 相似文献
7.
Alécio R. Nunes Aline O. Moura Alexandre G. S. Prado 《Journal of Thermal Analysis and Calorimetry》2011,106(2):445-452
H-magadiite was applied to remove the pesticides 2,4-d, diuron, and atrazine from water. The H-magadiite containing herbicides adsorbed were investigated by FTIR, DRX, N2 adsorption and desorption isotherms, and surface area. Calorimetric studies were carried out to determine the heat of interaction
between pesticides and magadiite. It was possible to ride the cycle of interaction of magadiite–pesticide for a better understanding
of the process involved. From the results of the thermal effect of the interaction of magadiite–pesticide, the thermochemical
parameters can be determined by using the relationship between the data obtained from adsorption and calorimetry results.
The interaction of pesticide–magadiite follows the sequence of adsorption: diuron > atrazine > 2,4-d. The ΔH values for the interactions were determined to be −20.62 ± 1.08, −24.04 ± 0.86–26.34 ± 0.93 kJ mol−1 for 2,4-d, diuron and atrazine, respectively. All the interactions were spontaneous, enthalpically and entropically favored demonstrating
the effectiveness and efficiency of the method. 相似文献
8.
C. G. Mothé A. D. Azevedo W. S. Drumond S. H. Wang 《Journal of Thermal Analysis and Calorimetry》2010,101(1):229-233
Samples of poly(l,l-lactide)-block-poly(ethylene glycol)-block-poly(l,l-lactide) (PLLA-PEG-PLLA) were synthesized from l,l-lactide polymerization using stannous 2-ethylhexanoate, Sn(Oct)2 as initiator and di-hydroxy-terminated poly(ethylene glycol) (PEG) (M
n
= 4000 g mol−1) as co-initiator. The chemical linkage between the PEG segment and the PLA segments was characterized by Fourier transform
infrared spectroscopy (FTIR). Thermogravimetry analysis (TG) revealed the copolymers composition and was capable to show the
deleterious effect of an excess of Sn(Oct)2 in the polymer thermal stability, while Differential Scanning Calorimetry (DSC) allowed the observation of the miscibility
between the PLLA and PEG segments in the different copolymers. 相似文献
9.
Rajeshwari V. Hosahalli Anita P. Savanur Sharanappa T. Nandibewoor Shivamurti A. Chimatadar 《Transition Metal Chemistry》2010,35(2):237-246
The oxidation of d-panthenol by MnO4
− was studied in the absence and in the presence of ruthenium(III) catalyst in alkaline medium at 298 K and at constant ionic
strength of 0.50 mol dm−3 by spectrophotometry. The stoichiometry in both the cases was [panthenol]: [MnO4
−] = 1:4. The oxidation products were identified by IR and GC–MS. The reaction was first-order with respect to both MnO4
− and ruthenium(III), while the orders with respect to both panthenol and alkali varied from first order to zero order as the
concentrations increased. The effects of added products, ionic strength and dielectric constant were studied. The reaction
constants, activation parameters and thermodynamic quantities were calculated for both the uncatalysed and catalysed reactions. 相似文献
10.
Ashok Kumar Singh Rajesh Kumar Singh Rashmi Srivastava Shalini Srivastava Jaya Srivastava Shahla Rahmani 《Transition Metal Chemistry》2010,35(3):349-355
The kinetics of oxidation of the sugars d(+)Melibiose (mel) and Cellobiose (cel) by N-bromoacetamide (NBA) in the presence of Rh(III) chloride as homogeneous catalyst in acidic medium at 45 °C have been investigated.
The reactions are first-order with respect to [NBA], [Rh(III)] and [substrate]. The rate is proportional to [H+]. No effects of [Hg(II)], [NHA] or [Cl−] on the rates were observed. Ionic strength and dielectric constant also have little effect. The observed kinetic data, available
literature and spectroscopic evidence lead us to conclude that NBAH+ and [RhCl5(H2O)]2− are the reactive species of NBA and Rh(III) chloride, respectively. The rate-determining step of the proposed reaction path
common for both sugars gives an activated complex by the interaction of a charged complex species and neutral sugar molecule,
which in the subsequent steps disproportionates into the reaction products with the regeneration of catalyst. The reactions
have been studied at four different temperatures and with the help of first-order rate constant values, various activation
parameters have been calculated. The main oxidation products of the reactions were identified as arabinonic acid, formic acid
and lyxonic acid in the case of mel and arabinonic acid and formic acid in the case of cel. 相似文献
11.
Electrospray ionization (ESI) mass spectra of hexoses, pentoses, and 2-deoxy-2-fluoro-d-glucose (FDG) were investigated and compared using liquid chromatography/mass spectroscopy (LC/MS). 18F-FDG is one of the most widely used radiopharmaceuticals. This work is aimed at the possible interpretations of ESI mass
spectra and at the comparison of various pentoses (arabinose, ribose, xylose), and hexoses (glucose, fructose, galactose,
mannose) which can be formed during the 18F-FDG’s synthesis or decomposition. As a result, nine major associates were found in the positive and four in the negative
mass spectra of all examined saccharides of which intensities and mass can be used with their retention times to determine
the saccharide. M · NH4+ and M · COOH− were identified as the most stable associates. 相似文献
12.
Dillip Kumar Baral Sudhanshu Sekhar Rout Jashoda Behera Sudam Chandra Si Prakash Mohanty 《Transition Metal Chemistry》2011,36(2):231-236
The kinetics and mechanism of the substitution reaction between [Cr(H2O)6]3+ and l-Dopa in aqueous medium has been studied over the range 1.8 ≤ pH ≤ 2.6, 1.68 × 10−2 mol dm−3 ≤ [Dopa] ≤ 5.04 × 10−2 mol dm−3, I = 0.1 mol dm−3 (KNO3) at 50 °C. The reaction takes place via an outer sphere association between Cr3+ and l-Dopa followed by chelation. The product was characterized by physicochemical and infrared spectroscopic methods. The antiparkinsonian
activity of the product was found to be higher than that of l-Dopa. 相似文献
13.
Balesh A. Deganatti Nagaraj P. Shetti Sharanappa T. Nandibewoor 《Transition Metal Chemistry》2009,34(2):143-152
The oxidation of l-valine (l-val) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 3.0 × 10−3 mol dm−3 was studied spectrophotometrically at 298 K and follows the rate law;
where K
4, K
5 and K
6 are the equilibrium constants for the different steps involved in the mechanism, k is the rate constant for the slow step of the reaction. The appearance of [l-val] term in both numerator and denominator explains the observed less than unit order in [l-val]. Similarly the appearances of [H3IO6
2−] and [OH−] in the denominator obey the experimental negative less than unit order in [H3IO6
2−] and [OH−], respectively. The oxidation reaction in alkaline medium proceeds via a DPC-l-valine complex, which decomposes slowly in a rate determining step followed by other fast steps to give the products. The
main products were identified by spot test and spectroscopic studies. 相似文献
14.
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
15.
Yun Wang Jin-Zhu Song Qian Yang Zhi-Hua Liu Xiao-Mei Huang Yan Chen 《Applied biochemistry and biotechnology》2010,162(3):843-854
A gene encoding chitin deacetylase was cloned by polymerase chain reaction from Aspergillus nidulans. Sequencing result showed 40% homology to the corresponding gene from Colletotrichum lindemuthianum. The complete gene contains an open reading frame of 747 nucleotides encoding a sequence of 249 amino acid residues. The
chitin deacetylase gene was subcloned into a pET28a expression vector and expressed in Escherichia coli BL21 and then purified by metal affinity chromatography using a His-bind column. The purified chitin deacetylase demonstrated
an activity of 0.77 U ml−1 for the glycol chitin substrates, and its specific activity was 4.17 U mg−1 for it. The optimal temperature and pH of the purified enzyme were 50 °C and 8.0, respectively. When glycol chitin was used
as the substrate, K
m was 4.92 mg ml−1, and K
cat showed 6.25 s−1, thus the ratio of K
cat and K
m was 1.27 ml s−1 mg−1. The activity of chitin deacetylase was affected by a range of metal ions and ethylenediaminetetraacetic acid. 相似文献
16.
The heat capacities of N-(tert-butoxycarbonyl)-l-phenylalanine (abbreviated to NTBLP in this article), as an important chemical intermediates used to synthesize proteins
and polypeptides, were measured by means of a fully automated adiabatic calorimeter over the temperature range from 78 to
350 K. The measured experimental heat capacities were fitted to a polynomial equation as a function of temperature. The thermodynamic
functions, H
T − H
298.15K and S
T − S
298.15K, were calculated based on the heat capacity polynomial equation in the temperature range of (80–350 K) with an interval of
5 K. The thermal stability of the compound was further studied using TG and DSC analyses; a possible mechanism for thermal
decomposition of the compound was suggested. 相似文献
17.
Lokendra Kumar Balvinder Singh Dilip Kumar Adhikari Joydeep Mukherjee Debashish Ghosh 《Applied biochemistry and biotechnology》2012,166(7):1723-1735
Purification and characterization of halotolerant, thermostable alkaline l-glutaminase from a Bacillus sp. LKG-01 (MTCC 10401), isolated from Gangotri region of Uttarakhand Himalaya, is being reported in this paper. Enzyme has
been purified 49-fold from cell-free extract with 25% recovery (specific activity 584.2 U/mg protein) by (NH4)2SO4 precipitation followed by anion exchange chromatography and gel filtration. Enzyme has a molecular weight of 66 kDa. l-Glutaminase is most active at pH 11.0 and stable in the pH range 8.0–11.0. Temperature optimum is 70 °C and is completely
stable after 3 h pre-incubation at 50 °C. Enzyme reflects more enhanced activity with 1–20% (w/v) NaCl, which is further reduced to 80% when NaCl concentration was increased up to 25%. l-Glutaminase is almost active with K+, Zn2+, and Ni2+ ions and K
m and V
max values of 240 μM and 277.77 ± 1.1 U/mg proteins, respectively. Higher specific activity, purification fold, better halo-tolerance,
and thermostability would make this enzyme more attractive for food fermentation with respect to other soil microbe derived
l-glutaminase reported so far. 相似文献
18.
Summary. Secreted peptides from diverse sources have been found to contain a d-amino acid. From the sequence of cloned mRNAs coding for the precursors of such peptides it could be deduced that in all cases tested so far the d-amino acid in the final product is derived from the corresponding l-amino acid present in the primary product of translation. Enzymes catalyzing such an l- to d-isomerization in peptide linkage have been isolated from the venom of a spider and the skin secretions of frogs. Even though
these are completely different proteins, the reaction mechanism is the same, namely a de-protonation/re-protonation of the
α-carbon of an amino acid with concomitant inversion of the chirality. Sequences potentially coding for homologues of the
frog enzyme are present in the genome of different vertebrate species. 相似文献
19.
Mark A. W. Lawrence Sonia E. Thomas Paul T. Maragh Tara P. Dasgupta 《Transition Metal Chemistry》2011,36(5):553-563
The kinetics of the intra-molecular electron transfer of an adduct of l-ascorbic acid and the [Fe3IIIO(CH3COO)6(H2O)3]+ cation in aqueous acetate buffer was studied spectrophotometrically, over the ranges 2.55 ≤ pH ≤ 3.74, 20.0 ≤ θ ≤ 35.0 °C,
at an ionic strength of 0.50 and 1.0 mol dm−3 (NaClO4). The reaction of l-ascorbic acid and the complex cation involves the rapid formation of an adduct species followed by a slower reduction in
the iron centres through consecutive one-electron transfer processes. The final product of the reaction is aqueous iron(II)
in acetate buffer. The proposed mechanism involves the triaqua and diaqua-hydroxo species of the complex cation, both of which
form adducts with l-ascorbic acid. At 25 °C, the equilibrium constant for the adduct formation was found to be 86 ± 15 and 5.8 ± 0.2 dm3 mol−1 for the triaqua and diaqua-hydroxo species, respectively. The kinetic parameters derived from the rate expression have been
found to be: k
0 = (1.12 ± 0.02) × 10−2 s−1 for the combined spontaneous decomposition and k
1 = (4.47 ± 0.06) × 10−2 s−1 (ΔH
1‡ = 51.0 ± 2.3 kJ mol−1, ΔS
1‡ = −100 ± 8 J K−1 mol−1), k
2 = (4.79 ± 0.38) × 10−1 s−1 (ΔH
2‡ = 76.5 ± 0.8 kJ mol−1, ΔS
2‡ = 6 ± 3 J K−1 mol−1) for the triaqua and diaqua-hydoxo species, respectively. 相似文献
20.
V. Ya. Kavun A. E. Panasenko L. A. Zemnukhova A. B. Slobodyuk 《Russian Chemical Bulletin》2008,57(7):1379-1383
Ionic mobility in the NaSbClF3 · H2O, KSbClF3, and NH4SbClF3 fluorochloride complexes was studied by 1H and 19F NMR spectroscopy in the temperature interval from 150 to 480 K. The types of ionic motions in the compounds were determined.
Their physicochemical characteristics were compared with those of the earlier studied sodium, potassium, and ammonium tetrafluoroantimonates(iii). The replacement of one F atom by the Cl atom in MSbF4 (M = Na, K, NH4) changes both the structure of the Sb polyhedra forming the structure of the antimony(iii) fluorochloride complex and the character of ionic motions in the compounds. The ionic conductivity in the 324–436 K range
was determined for NH4SbClF3: σ = 1.07 · 10−4 S cm−1 at T = 423 K.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1353–1357, July, 2008. 相似文献