共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
Endo H Hayashi Y Kitani Y Ren H Hayashi T Nagashima Y 《Analytical and bioanalytical chemistry》2008,391(4):1255-1261
l-Lysine (l-Lys) in living bodies is critical for metabolism; therefore, determination of its levels in food is important. Most enzymatic
methods for l-Lys analysis are performed using l-lysine oxidase (LyOx), but commercially manufactured LyOx is generally not highly selective for l-Lys among amino acids. We previously isolated LyOx as an antibacterial protein secreted from the skin of the rockfish Sebastes schlegeli. In the present study, we developed an optical enzyme sensor system for rapid and continuous determination of l-Lys using this LyOx. The system comprised an immobilized LyOx membrane, an optical oxygen probe, a flow system, and a personal
computer. The amount of l-Lys was detected as a decrease in the oxygen concentration due to the LyOx reaction. The specificity of the sensor was examined
against various amino acids. The sensor response was specific for l-Lys. Good reproducibility was obtained in 58 assays. The response of the sensor using commercially prepared LyOx was unstable
compared with the response using LyOx isolated in our laboratory. Our sensor system could be used for 5 weeks without our
having to change the enzyme membrane. The calibration curve for a standard l-Lys solution was linear from 0.1 to 3.0 mmol L−1. One assay could be completed within 2 min. The sensor was applied to determine the l-Lys content in food samples such as bonito cooking water and scallop hepatopancreas. The values obtained using the sensor
and conventional high-performance liquid chromatography methods were well correlated. 相似文献
3.
Hatanaka T Usuki H Arima J Uesugi Y Yamamoto Y Kumagai Y Yamasato A Mukaihara T 《Applied biochemistry and biotechnology》2011,163(7):836-844
l-Asparaginase (ASNase) has proved its use in medical and food industries. Sequence-based screening showed the thermophilic
Streptomyces strain Streptomyces thermoluteus subsp. fuscus NBRC 14270 (14270 ASNase) to positive against predicted ASNase primary sequences. The 14270 ASNase gene and four l-asparaginase genes from Streptomyces coelicolor, Streptomyces avermitilis, and Streptomyces griseus (SGR ASNase) were expressed in Streptomyces lividans using a hyperexpression vector: pTONA5a. Among those genes, only 14270 ASNase and SGR ASNase were successful for overexpression and detected in culture supernatants
without an artificial signal peptide. Comparison of the two Streptomyces enzymes described above demonstrated that 14270 ASNase was superior to SGR ASNase in terms of optimum temperature, thermal
stability, and pH stability. 相似文献
4.
The integral enthalpies of dissolution Δsol
H
m of l-cysteine and l-asparagine in mixtures of water with acetonitrile and dimethyl sulfoxide at the concentration of organic solvent up to 0.32
molar fractions were measured by means of dissolution calorimetry. The standard enthalpies of dissolution (Δsol
H°) and transfer (Δtrans
H°) of the amino acids from water to a mixed solvent were calculated. The enthalpy coefficients of pair interactions for L-cysteine
and L-asparagine with cosolvent molecules are positive, except for the L-asparagine-water-acetonitrile system. The concepts
on the prevailing effect of specific interactions in solutions and the influence of the nature of the cosolvents and lateral
substituents of the amino acids on the thermochemical characteristics of dissolution were used to explain the data obtained. 相似文献
5.
l-asparaginase (LA) catalyzes the degradation of asparagine, an essential amino acid for leukemic cells, into ammonia and aspartate. Owing to its ability to inhibit protein biosynthesis in lymphoblasts, LA is used to treat acute lymphoblastic leukemia (ALL). Different isozymes of this enzyme have been isolated from a wide range of organisms, including plants and terrestrial and marine microorganisms. Pieces of information about the three-dimensional structure of l-asparaginase from Escherichia coli and Erwinia sp. have identified residues that are essential for catalytic activity. This review catalogues the major sources of l-asparaginase, the methods of its production through the solid state (SSF) and submerged (SmF) fermentation, purification, and characterization as well as its biological roles. In the same breath, this article explores both the past and present applications of this important enzyme and discusses its future prospects. 相似文献
6.
Shadpour Mallakpour Samaneh Soltanian Mohammad R. Sabzalian 《Colloid and polymer science》2011,289(1):93-100
A series of biodegradable functional amino-acid-based poly(ester-imide)s (PEI)s were designed and synthesized by the direct
polycondensation reaction of chiral diacids composed of naturally occurring α-amino acids with 4,4′-thiobis(2-tert-butyl-5-methylphenol) in the presence of tosyl chloride, pyridine, and N,N-dimethylformamide as a condensing agent. These new chiral polymers were characterized with respect to chemical structure
and purity using specific rotation experiments, FT-IR, 1H-NMR, techniques, and elemental analysis. The surface morphology of these polymers was investigated by field emission scanning
electron microscopy. The result indicated nanoscale morphology of the obtained polymers. Thermal stability and the weight
loss behavior of the resulting PEIs were studied by TGA techniques. All PEIs showed no significant weight loss below 400 °C
in a N2 environment. The monomers and prepared polymers were co-cultivated with airborne fungal spores in culture media to study
their biological activity. Soil burial test was also used for evaluation of their biodegradation behavior. The results showed
that the synthesized monomers and their derived polymers are biologically active and that their degradation products are probably
nontoxic to microbial growth. 相似文献
7.
Béatrice Nicolaï Nathalie Mahé René Céolin Ivo B. Rietveld Maria Barrio Josep-Lluis Tamarit 《Structural chemistry》2011,22(3):649-659
l-Tyrosine alkyl esters are used as prodrugs for l-tyrosine. Although prodrugs are often designed for their behavior in solution, understanding their solid-state properties is the first step in mastering drug delivery. The crystal structure of l-tyrosine methyl ester has been determined and compared to published structures of l-tyrosine and its ethyl and n-butyl esters. It is almost isostructural with the other esters: it crystallizes in the orthorhombic chiral space group P212121, a = 5.7634(15) Å, b = 12.111(2) Å, c = 14.3713(19) Å, V = 1003.1(4) Å3 with Z′ = 1. Their main packing motif is a C(9) infinite hydrogen-bond chain, but the conformation of l-tyrosine methyl ester is different from the other two: eclipsed versus U-shaped, respectively. The published structure of the ethyl ester, which was incomplete, has been confirmed by X-ray powder diffraction data. Because l-tyrosine methyl ester is very stable (28 years stored at room temperature), and its hydrolysis rate is relatively low, it should be one of the better prodrugs among the alkyl esters of tyrosine. 相似文献
8.
Małgorzata Pająk Katarzyna Pałka Elżbieta Winnicka Marianna Kańska 《Journal of Radioanalytical and Nuclear Chemistry》2018,317(2):643-666
This review compiles the combined chemical and enzymatic synthesis of aromatic l-amino acids (l-phenylalanine, l-tyrosine, l-DOPA, l-tryptophan, and their derivatives and precursors) specifically labeled with carbon and hydrogen isotopes, which were elaborated in our research group by the past 20 years. These compounds could be then employed to characterize the mechanisms of enzymatic reactions via kinetic and solvent isotope effects methods. 相似文献
9.
Désirée L. Röhlen Johanna Pilas Michael J. Schöning Thorsten Selmer 《Applied biochemistry and biotechnology》2017,183(2):566-581
Three amperometric biosensors have been developed for the detection of l-malic acid, fumaric acid, and l -aspartic acid, all based on the combination of a malate-specific dehydrogenase (MDH, EC 1.1.1.37) and diaphorase (DIA, EC 1.8.1.4). The stepwise expansion of the malate platform with the enzymes fumarate hydratase (FH, EC 4.2.1.2) and aspartate ammonia-lyase (ASPA, EC 4.3.1.1) resulted in multi-enzyme reaction cascades and, thus, augmentation of the substrate spectrum of the sensors. Electrochemical measurements were carried out in presence of the cofactor β-nicotinamide adenine dinucleotide (NAD+) and the redox mediator hexacyanoferrate (III) (HCFIII). The amperometric detection is mediated by oxidation of hexacyanoferrate (II) (HCFII) at an applied potential of + 0.3 V vs. Ag/AgCl. For each biosensor, optimum working conditions were defined by adjustment of cofactor concentrations, buffer pH, and immobilization procedure. Under these improved conditions, amperometric responses were linear up to 3.0 mM for l-malate and fumarate, respectively, with a corresponding sensitivity of 0.7 μA mM?1 (l-malate biosensor) and 0.4 μA mM?1 (fumarate biosensor). The l-aspartate detection system displayed a linear range of 1.0–10.0 mM with a sensitivity of 0.09 μA mM?1. The sensor characteristics suggest that the developed platform provides a promising method for the detection and differentiation of the three substrates. 相似文献
10.
11.
Glycyl-l-proline (Gly-l-Pro) is the main degradation product of collagen and is a good diagnostic tool in various pathological conditions. The aim
of this work was to prepare dipeptide Gly-l-Pro labeled with 99mTc. Complex preparation was carried out under alkaline reaction conditions and its stability was assessed 10 and 120 min after
preparation. The formation of two types of complex compounds was observed. High-performance liquid chromatography, paper electrophoresis,
paper chromatography and thin layer chromatography were employed to monitor the formation of different complexes. Molecular
modeling (semi-empirical method) was used to design their structure and composition. First complex cI with formula [TcO(Gly-l-Pro)]−1 is unstable. After 120 min cI is completely transformed to complex cII with formula Tc(Gly-l-Pro)3. 相似文献
12.
Chen N Huang J Feng ZB Yu L Xu QY Wen TY 《Applied biochemistry and biotechnology》2009,158(3):595-604
In this study, the fed-batch fermentation technique was applied to improve the yield of l-threonine produced by Escherichia coli TRFC. Various fermentation substrates and conditions were investigated to identify the optimal carbon source, its concentration
and C/N ratio in the production of l-threonine. Sucrose was found to be the optimal initial carbon source and its optimal concentration was determined to be 70 g/L
based on the results of fermentations conducted in a 5-L jar fermentor using a series of fed-batch cultures of E. coli TRFC. The effects of glucose concentration and three different feeding methods on the production of l-threonine were also investigated in this work. Our results showed that the production of l-threonine by E. coli was enhanced when glucose concentration varied between 5 and 20 g/L with DO-control pulse fed-batch method. Furthermore,
the C/N ratio was a more predominant factor than nitrogen concentration for l-threonine overproduction and the optimal ratio of ammonium sulfate to sucrose (g/g) was 30. Under the optimal conditions, a final l-threonine concentration of 118 g/L was achieved after 38 h with the productivity of 3.1 g/L/h (46% conversion ratio from
glucose to threonine). 相似文献
13.
Ni-Ning Hong Guang Yang Jian Li Yao-Ping Zhang 《Applied biochemistry and biotechnology》2009,158(2):398-407
A genetically engineered Escherichia coli was developed as the source of enzyme for rapidly quantifying glutamine. E. coli BL21 (DE3) cells overexpressing a glutamine synthetase from Bacillus subtilis were prepared as tube aliquots and used in a small volume of nontoxic mixture. The current method was compared to high performance
liquid chromatography analysis, Sigma kit (GLN-1) and Mecke method. The method is applicable to a wide range of glutamine
concentrations (0.05–2.5 mM) and correlates well to the detection results obtained from high performance liquid chromatography
(Pearson correlation is 0.978 at the 0.01 level). Moreover, the whole assay procedure takes less than 15 min and uses nontoxic
reagents, so it can be applied to monitor glutamine production and utilization conveniently. 相似文献
14.
Manish G. Yadav Monali R. Kavadia Rajeshkumar N. Vadgama Annamma A. Odaneth Arvind M. Lali 《Applied biochemistry and biotechnology》2018,184(4):1168-1186
l-ascorbyl palmitate (ASP) is an oil-soluble derivative of ascorbic acid which is used extensively in food, cosmetics industry, and medical hygiene. Enzymatic synthesis of ascorbyl palmitate in tert-butyl alcohol was carried out using indigenously immobilized lipase preparation PyCal with ascorbic acid and palmitic acid as starting material. The developed batch process under optimized reaction conditions resulted in conversion of 90% with relatively shorter reaction time of 6 h. Continuous process in packed bed reactor gave conversion of 50% with space time yield of 15.46 g/L/h which was found to be higher than the reported literature on enzymatic synthesis of ascorbyl palmitate. The immobilized lipase used in the present work showed good reusability. Characterization of formed ascorbyl palmitate was carried out by FTIR, MS/MS, H1-NMR, and C13-NMR. The enzymatic process resulted in selective synthesis of 6-O-l-ascorbyl palmitate with purity of 98.6% and no side product formation. The use of underivatized starting materials, high space time yield of 15.46 g L?1 h?1, high recyclability of catalyst, and no by-product formation make the overall process highly efficient and clean in terms of energy consumption and waste generation, respectively. The optimized reaction parameters for ascorbyl palmitate synthesis in the present study can be used as a useful reference for industrial synthesis of fatty acid esters of ascorbic acid by enzymatic route. 相似文献
15.
Corncob is an economic feedstock and more than 20 million tons of corncobs are produced annually in China. Abundant xylose
can be potentially converted from the large amount of hemicellulosic materials in corncobs, which makes the crop residue an
attractive alternative substrate for a value-added production of a variety of bioproducts. Lactic acid can be used as a precursor
for poly-lactic acid production. Although current industrial lactic acid is produced by lactic acid bacteria using enriched
medium, production by Rhizopus oryzae is preferred due to its exclusive formation of the l-isomer and a simple nutrition requirement by the fungus. Production of l-(+)-lactic acid by R. oryzae using xylose has been reported; however, its yield and conversion rate are poor compared with that of using glucose. In this
study, we report an adapted R. oryzae strain HZS6 that significantly improved efficiency of substrate utilization and enhanced production of l-(+)-lactic acid from corncob hydrolysate. It increased l-(+)-lactic acid final concentration, yield, and volumetric productivity more than twofold compared with its parental strain.
The optimized growth and fermentation conditions for Strain HZS6 were defined. 相似文献
16.
Hong-Ge Jia Yong-Qiang Shi Li-Qun Ma Ya-Zhen Wang Yu Zang Ji-Jun Peng 《Chemical Papers》2015,69(5):756-760
The Rh(nbd)(l-proline) (nbd = 2,5-norbornadiene) catalyst was synthesised with l-proline as ligand. The achiral monomer phenylacetylene, having two hydroxyl groups and a dodecyl group (DoDHPA), was polymerised for the first time using an isolated chiral Rh(nbd)(l-proline) as catalyst to afford polymers of Mr of 28.5 × 104 and 36.2 × 104. The resulting polymers exhibited the Cotton effect at wavelengths assignable to the main chain, indicating that the polymers adopted one-handed helical conformation. These findings suggest that the rhodium complex with chiral amine may be the true active species for helix-sense-selective polymerisation (HSSP) of DoDHPA. 相似文献
17.
The structural transition of the l- and dl forms of poly(N-(1- hydroxymethyl)propylmethacrylamide (PHMPMA) in aqueous solution was studied by measuring the pressure dependence of the apparent scattering intensity, differential scanning calorimetry (DSC), and circular dichroism (CD). The thermodynamic implications of the results are discussed in relation to the chiral structure of the side chain, and differences in the thermal and barometric transitions. T-P diagrams of the transition showed characteristic ellipsoid features. Antagonism of the temperature and pressure effects was observed only for P(dl-HMPMA). For P(l-HMPMA), the transition temperature (T
tr) decreased with increasing pressure, and the highest T
tr was observed at atmospheric pressure (0.1 MPa). For both polymers, the highest P
trs were observed at the lowest temperatures. The l polymer showed a specific negative peak in its CD spectrum at around 220 nm in the lower temperature region and the temperature dependence was reproduced by a single-step transition, with the midpoint corresponding to the T
tr obtained from the scattering measurements. Coupled with the results from the DSC, the different behavior between the P(l-HMPMA) and P(dl-HMPMA) could be explained in terms of the chain states before and after the transition. The cooperative factors derived from the DSC measurement revealed that about 4 to 5 polymers of the present size were necessary to perform a thermal transition for P(l-HMPMA), and that P(dl-HMPMA) underwent its transition as an almost single molecular event.This revised version was published online in June 2005 with correction to the article category. 相似文献
18.
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
19.
The imperative role of functionalized natural alginate in immobilization of Lactobacillus delbrucekii (NCIM 2365) cells in production of optically pure L (+) lactic acid was studied. L. delbrucekii cells were immobilized in alginate, succinylated alginate and carrageenan to evaluate the bead stability and selectivity towards production of optically pure L (+) lactic acid. The scanning electron microscopic studies of free and immobilized cells show little morphological changes. The present study highlights the use of functionalized alginate-immobilized L. delbrucekii cells in production of L (+) lactic acid in higher yields (0.93 Yp/s in grams) with an improved enantioselectivity (99%). In addition, they further revealed decreased by-product formation (acetic and propionic acid) when compared to free and other immobilized cell fermentation. 相似文献
20.
Qiang Li Bijun Liu Yin Tian Qianhong Yu Wanjun Mu Hongyuan Wei Dongqi Wang Xingliang Li Shunzhong Luo 《Journal of solution chemistry》2017,46(5):1048-1058
N-(phosphonomethyl)-l-proline is an analogue of glyphosate. The protonation for N-(phosphonomethyl)-l-proline was studied by potentiometry, calorimetry, 31P NMR spectroscopy and quantum chemical calculations to further understand the protonation process of glyphosate. The results confirmed that the order of successive protonation sites of totally deprotonated N-(phosphonomethyl)-l-proline are a phosphonate oxygen, amino nitrogen, and finally the carboxylate oxygen. The results can improve the understanding of the biological activity of these types of molecules in solution. 相似文献