首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 531 毫秒
1.
The three new dual-layer matrices (polyacrylonitrile (PAN) membranes coated with physically bound chitosan (CHI)—PANCHI-A and chemically bound chitosan—PANCHI-B and PANCHI-C) for immobilization of acetylcholinesterase (AChE) were obtained. The chemical-modified PAN membrane (PAN-NaOH + ethylenediamine (EDA)) was used as a base for the prepared dual-layer membranes. For chemical chitosan bound membrane, chitosan was tethered onto the membrane surface to form a dual-layer biomimetic membrane in the presence of glutaraldehyde (GA). The basic characteristics (amount of amino groups, hydrophilicity and transport characteristics) of the chitosan-modified membranes were investigated. The SEM analyses were shown essential morphology change in the different chitosan membranes.The relative activities and Vmax of the covalently immobilized enzyme on PANCHI-B and PANCHI-C membranes were higher than that on PANCHI-A membrane and chemical-modified membrane with NaOH + EDA. Km values for the different modified membranes are lower for the chitosan-treated membranes. The pH and temperature optimum of immobilized enzyme were determined. The bound enzymes on PANCHI-B and PANCHI-C have higher thermal and storage stability in comparison with AChE on PANCHI-A membrane and free enzyme.  相似文献   

2.
3.
Poly(itaconic acid) grafted and/or Fe(III) ions incorporated chitosan membranes were used for reversible immobilization of catalase (from bovine liver) via adsorption. The influences of pH and initial catalase concentration on the immobilization capacities of the CH-g-poly(IA) and CH-g-poly(IA)-Fe(III) membranes have been investigated in a batch system. Maximum catalase adsorption onto CH-g-poly(IA) and CH-g-poly(IA)-Fe(III) membrane were found to be 6.3 and 37.8 mg/g polymer at pH 5.0 and 6.5, respectively. The CH-g-poly(IA)-Fe(III) membrane with high catalase adsorption capacity was used in the rest of the study. The Km value for immobilized catalase on CH-g-poly(IA)-Fe(III) (25.8 mM) was higher about 1.6-fold than that of free enzyme (13.5 mM). Optimum operational temperature was observed at 40 °C, a 5 °C higher than that of the free enzyme and was significantly broader. The optimum operational pH was same for both free and immobilized catalase (pH 7.0). Thermal stability was found to increase with immobilization. Free catalase lost all its activity within 20 days whereas immobilized catalase lost 23% of its activity during the same incubation period. It was observed that the same support enzyme can be repeatedly used for immobilization of catalase after regeneration without significant loss in adsorption capacity or enzyme activity. In addition, the CH-g-poly(IA)-Fe(III) membrane prepared in this work showed promising potential for various biotechnological applications.  相似文献   

4.
β-Glucosidase immobilized on magnetic chitosan microspheres for potential recycling usage in hydrolysis of cellulosic biomass was investigated. The immobilized enzyme had an activity of 6.4 U/g support under optimized condition when using cellobiose as substrate. Immobilization resulted in less increase of the apparent Km, low drift of the optimal pH, as well as improved stability relative to the free enzyme. The immobilized β-glucosidase was applied to enzymatic hydrolysis of corn straw to produce 60.2 g/l reducing sugar with a conversion rate of 78.2% over the course of a 32-h reaction. This conversion rate was maintained above 76.5% after recycling the enzyme for use in eight batches (total 256 h), showing favorable operational stability of the immobilized enzyme.  相似文献   

5.
The synthesis of chitosan (Chs) and chitin (Chi) copolymer and grafting of acrylamide (AAm) onto the synthesized copolymer have been carried out by chemical methods. The grafted copolymer was characterized by FTIR, SEM and XRD. The extracellular cutinase of Aspergillus sp. RL2Ct (E.C. 3.1.1.3) was purified to 4.46 fold with 16.1% yield using acetone precipitation and DEAE sepharose ion exchange chromatography. It was immobilized by adsorption on the grafted copolymer. The immobilized enzyme was found to be more stable then the free enzyme and has a good binding efficiency (78.8%) with the grafted copolymer. The kinetic parameters KM and Vmax for free and immobilized cutinase were found to be 0.55 mM and 1410 μmol min−1 mg−1 protein, 2.99 mM and 996 μmol min−1 mg−1 protein, respectively. The immobilized cutinase was recycled 64 times without considerable loss of activity. The matrix (Chs-co-Chi-g-poly(AAm)) prepared and cutinase immobilized on the matrix have potential applications in enzyme immobilization and organic synthesis respectively.  相似文献   

6.
《Process Biochemistry》2014,49(10):1682-1690
Double enzymes (alcalase and trypsin) were effectively immobilized in a composite carrier (calcium alginate–chitosan) to produce immobilized enzyme beads referred to as ATCC. The immobilization conditions for ATCC were optimized, and the immobilized enzyme beads were characterized. The optimal immobilization conditions were 2.5% of sodium alginate, 10:4 sodium alginate to the double enzymes, 3:7 chitosan solution to CaCl2 and 2.5 h immobilization time. The ATCC beads had greatly enhanced stability and good usability compared with the free form. The ATCC residual activity was retained at 88.9% of DH (degree of hydrolysis) after 35 days of storage, and 36.0% of residual activity was retained after three cycles of use. The beads showed a higher zein DH (65.8%) compared with a single enzyme immobilized in the calcium alginate beads (45.5%) or free enzyme (49.3%). The ATCC kinetic parameters Vmax and apparent Km were 32.3 mL/min and 456.62 g−1, respectively. Active corn peptides (CPs) with good antioxidant activity were obtained from zein in the ethanol phase. The ATCC might be valuable for preparing CPs and industrial applications.  相似文献   

7.
An investigation was conducted on the production of β-galactosidase (β-gal) by different strains of Kluyveromyces, using lactose as a carbon source. The maximum enzymatic activity of 3.8 ± 0.2 U/mL was achieved by using Kluyveromyces lactis strain NRRL Y1564 after 28 h of fermentation at 180 rpm and 30 °C. β-gal was then immobilized onto chitosan and characterized based on its optimal operation pH and temperature, its thermal stability and its kinetic parameters (Km and Vmax) using o-nitrophenyl β-d-galactopyranoside as substrate. The optimal pH for soluble β-gal activity was found to be 6.5 while the optimal pH for immobilized β-gal activity was found to be 7.0, while the optimal operating temperatures were 50 °C and 37 °C, respectively. At 50 °C, the immobilized enzyme showed an increased thermal stability, being 8 times more stable than the soluble enzyme. The immobilized enzyme was reused for 10 cycles, showing stability since it retained more than 70% of its initial activity. The immobilized enzyme retained 100% of its initial activity when it was stored at 4 °C and pH 7.0 for 93 days. The soluble β-gal lost 9.4% of its initial activity when it was stored at the same conditions.  相似文献   

8.
Acetylcholinesterase (AChE) was immobilized on chemically modified poly-(acrylonitrile-methyl-methacrylate-sodium vinylsulfonate) membranes in accordance with three different methods, the first of which involved random enzyme immobilization via glutaraldehyde, the second one—site-specific enzyme immobilization via glutaraldehyde and Concanavalin A (Con A) and the third method—modified site-specific enzyme immobilization via glutaraldehyde in the presence of a mixture of multiwall carbon nanotubes and albumin (MWCNs + BSA), glutaraldehyde and Con A. Preliminary tests for the activity of immobilized AChE were carried out using these three methods. The third method was selected as the most efficient one for the immobilization of AChE and the prepared enzyme carriers were used for the construction of amperometric biosensors for the detection of acetylthiocholine (ATCh).A five level three factorial central composite design was chosen to determine the optimal conditions for the enzyme immobilization with three critical variables: concentration of enzyme, Concanavalin A and MWCNs. The design illustrated that the optimum values of the factors influencing the amperometric current were CE: 70 U mL−1; CCon A: 1.5 mg mL−1 and CMWCN: 11 mg mL−1, with an amperometric current 0.418 μA. The basic amperometric characteristics of the constructed biosensor were investigated. A calibration plot was obtained for a series of ATCh concentrations ranging from 5 to 400 μM. A linear interval was detected along the calibration curve from 5 to 200 μM. The correlation coefficient for this concentration range was 0.995. The biosensor sensitivity was calculated to be 0.065 μA μM−1 cm−2. The detection limit with regard to ATCh was calculated to be 0.34 μM. The potential application of the biosensor for detection and quantification of organophosphate pesticides was investigated as well. It was tested against sample solutions of Paraoxon. The biosensor detection limit was determined to be 1.39 × 10−12 g L−1 of Paraoxon, as well as the interval (10−11 to 10−8 g L−1) within which the biosensor response was linearly dependant on the Paraoxon concentration. Finally the storage stability of the enzyme carrier was traced for a period of 120 days. After 30-day storage the sensor retained 76% of its initial current response, after 60 days—68% and after 120 days—61%.  相似文献   

9.
Proton conducting biopolymer networks have potential use for bio-sensors. The cost-effective, non-hazardous and environmentally safe biopolymer, such as chitosan, is an attractive feature for bio-sensors. Cholesterol oxidase was immobilized in conducting network via complexation of chitosan with alginic acid. A method for the preparation of the complex along with characterization by elemental analysis, FTIR spectroscopy, TGA and DSC were reported. The proton conductivity chitosan–alginic acid network was studied via impedance spectroscopy under humidified condition. The complex polymer electrolyte with x = 1 exhibited maximum proton conductivity of 1.4 × 10?3 S/cm at RT, RH  50%. The potential use of this network in enzyme immobilization was studied by manufacturing cholesterol oxidase entrapped polymer networks. Additionally, the maximum reaction rate (Vmax) and Michaelis–Menten constant (Km) were investigated for the immobilized cholesterol oxidase. Also, temperature and pH optimization studies were performed, and operational stability and shelf life of the polymer network were examined.  相似文献   

10.
We investigated the production of chitosan oligosaccharides by continuous hydrolysis of chitosan in an enzyme membrane bioreactor, with the goal of improving the yield of physiologically active oligosaccharides (pentamers and hexamers) and achieving operational stability. The bioreactor was a continuous-flow stirred-tank reactor equipped with an ultrafiltration membrane with a molecular weight cut-off of 2000 Da, and the hydrolysis was accomplished with chitosanase from Bacillus pumilus. After optimization of the reaction parameters, such as the amount of enzyme, the yield of the target oligosaccharides produced in the membrane bioreactor with free chitosanase reached 52% on the basis of the fed concentration of chitosan. An immobilized chitosanase prepared by the multipoint attachment method was used to improve the operational stability of the membrane bioreactor. Under the optimized conditions, pentameric and hexameric chitosan oligosaccharides were steadily produced at 2.3 g/L (46% yield) for a month. The half-life of the productivity of the reactor was estimated to be 50 d under the conditions examined.  相似文献   

11.
β-Galactosidase is an important enzyme catalyzing not only the hydrolysis of lactose to the monosaccharides glucose and galactose but also the transgalactosylation reaction to produce galacto-oligosaccharides (GOS). In this study, β-galactosidase was immobilized by adsorption on a mixed-matrix membrane containing zirconium dioxide. The maximum β-galactosidase adsorbed on these membranes was 1.6 g/m2, however, maximal activity was achieved at an enzyme concentration of around 0.5 g/m2. The tests conducted to investigate the optimal immobilization parameters suggested that higher immobilization can be achieved under extreme parameters (pH and temperature) but the activity was not retained at such extreme operational parameters. The investigations on immobilized enzymes indicated that no real shift occurred in its optimal temperature after immobilization though the activity in case of immobilized enzyme was better retained at lower temperature (5 °C). A shift of 0.5 unit was observed in optimal pH after immobilization (pH 6.5 to 7). Perhaps the most striking results are the kinetic parameters of the immobilized enzyme; while the Michaelis constant (Km) value increased almost eight times compared to the free enzyme, the maximum enzyme velocity (Vmax) remained almost constant.  相似文献   

12.
Extracellular laccase produced by the wood-rotting fungus Cerrena unicolor was immobilized covalently on the mesostructured siliceous cellular foams (MCFs) functionalised using various organosilanes with amine and glycidyl groups. The experiments indicated that laccase bound via glutaraldehyde to MCFs modified using 2-aminoethyl-3-aminopropyltrimethoxysilane remains very active. In the best biocatalyst activity was about 42,700 U mL?1 carrier (66,800 U mg?1 bound protein), and hence significantly higher than ever reported before. Optimisation of the immobilization procedure with respect to protein concentration, pH of coupling mixture and the enzyme purity afforded the biocatalyst with activity of about 90,980 U mL?1. For the best preparation, thermal- and pH-stability, and activity profiles were determined. Experiments carried out in a batch reactor showed that kcat/Km for immobilized enzyme (0.88 min?1 μM?1) was acceptable lower than the value obtained for the native enzyme (2.19 min?1 μM?1). Finally, potentials of the catalysts were tested in the decolourisation of indigo carmine without redox-mediators. Seven consecutive runs with the catalysts separated by microfiltration proved that adsorption of the dye onto the carrier and enzymatic oxidation contribute to the efficient decolourisation without loss of immobilized enzyme activity.  相似文献   

13.
An industrial enzyme, alkaline serine endopeptidase, was immobilized on surface modified SBA-15 and MCF materials by amide bond formation using carbodiimide as a coupling agent. The specific activities of free enzyme and enzyme immobilized on SBA-15 and MCF were studied using casein (soluble milk protein) as a substrate. The highest activity of free enzyme was obtained at pH 9.5 while this value shifted to pH 10 for SBA-15 and MCF immobilized enzyme. The highest activity of immobilized enzymes was obtained at higher temperature (60 °C) than that of the free enzyme (55 °C). Kinetic parameters, Michaelis–Menten constant (Km) and maximum reaction velocity (Vmax), were calculated as Km = 13.375, 11.956, and 8.698 × 10?4 mg/ml and Vmax = 0.156, 0.163 and 0.17 × 10?3 U/mg for the free enzyme and enzyme immobilized on SBA-15 and MCF, respectively. The reusability of immobilized enzyme showed 80% of the activity retained even after 15 cycles. Large pore sized MCF immobilized enzyme was found to be more promising than the SBA-15 immobilized enzyme due to the availability of larger pores of MCF, which offer facile diffusion of substrate and product molecules.  相似文献   

14.
A non-modified and modified with NaOH and ethylenediamine ultrafiltration membranes prepared from AN copolymer have been used as carriers for the immobilization of horseradish peroxidase (HRP) enzyme. The amount of bound protein onto the membranes and the activity of the immobilized enzyme have been investigated as well as the pH and thermal optimum, and the thermal stability of the free and immobilized HRP. The experiments have proved that the modified membrane is a better support for the immobilization of HRP enzyme. The latter has shown a greater thermal stability than the free enzyme.A possible application has been studied for reducing phenol concentration in water solutions through oxidation of phenol by hydrogen peroxide, in the presence of free and immobilized HRP enzyme on modified AN copolymer membranes. A higher degree of the phenol oxidation has been observed in the presence of the immobilized enzyme. A total removal of phenol has been achieved in the presence of immobilized HRP at concentration of the hydrogen peroxide 0.5 mmol L?1 and concentration of the phenol in the model solutions within the interval 5–40 mg L?1. A high degree of phenol oxidation (95.4%) has been achieved in phenol solution with 100 mg L?1 concentration in the presence of hydrogen peroxide and immobilized HRP, which demonstrates the promising opportunity of using the enzyme for bioremediation of waste waters, containing phenol.The immobilized HRP has shown good operational stability. Deactivation of the immobilized enzyme to 50% of the initial activity has been observed after the 20th day of the enzyme operation.  相似文献   

15.
An amperometric biosensor was developed for determination of urea using electrodeposited rhodium on a polymer membrane and immobilized urease. The urease catalyzes the hydrolysis of urea to NH4+ and HCO3 ions and the liberated ammonia is catalytically and electrochemically oxidized by rhodium present in the rhodinized membrane on the Pt working electrode. Three types of rhodinized polymer membranes were prepared by varying the number of electrodeposition cycles: membrane 1 with 10 deposition cycles, membrane 2 with 40 cycles and membrane 3 with 60 cycles. The morphologies of the rhodinized membranes were investigated by scanning electron microscopy and the results showed that the deposition of rhodium was like flowers with cornices-like centers. The influence of the amount of electrodeposited rhodium over the electrode sensitivity to different concentrations of ammonia was examined initially based on the cyclic voltammetric curves using the three rhodium modified electrodes. The obtained results convincingly show that electrode with rhodinized membrane 1, which contain the lowest amount of electrodeposited rhodium is the most active and sensitive regarding ammonia. It was found that the anodic oxidation peak of ammonia to nitrogen occurs at 0.60 V. In order to study the performance of urease amperometric sensor for the determination of urea, experiments at constant potential (0.60 V) were performed. The current–time experiments were carried out with urease rhodinized membrane 1 (10 cycles). The amperometric response increased linearly up to 1.75 mM urea. The detection limit was 0.05 mM. The urea biosensor exhibited a high sensitivity of 1.85 μA mM−1 cm−2 with a response time 15 s. The Michaelis–Menten constant Km for the urea biosensor was calculated to be 6.5 mM, indicating that the immobilized enzyme featured a high affinity to urea. The urea sensor showed a good reproducibility and stability. Both components rhodium and urease contribute to the decreasing of the production cost of biosensor by avoiding the use of a second enzyme.  相似文献   

16.
《Process Biochemistry》2014,49(12):2149-2157
The cell-bound cholesterol oxidase from the Rhodococcus sp. NCIM 2891 was purified three fold by diethylaminoethyl–sepharose chromatography. The estimated molecular mass (SDS-PAGE) and Km of the enzyme were ∼55.0 kDa and 151 μM, respectively. The purified cholesterol oxidase was immobilized on chitosan beads by glutaraldehyde cross-linking reaction and immobilization was confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray analysis. The optimum temperature (45 °C, 5 min) for activity of the enzyme was increased by 5 °C after immobilization. Both the free and immobilized cholesterol oxidases were found to be stable in many organic solvents except for acetone. Fe2+ and Pb2+ at 0.1 mM of each acted as inhibitors, while Ag+, Ca2+, Ni2+ and Zn2+ activated the enzyme at similar concentration. The biotransformation of cholesterol (3.75 mM) with the cholesterol oxidase immobilized beads (3.50 U) leads to ∼88% millimolar yield of cholestenone in a reaction time of 9 h at 25 °C. The immobilized enzyme retains ∼67% activity even after 12 successive batches of operation. The biotransformation method thus, shows a great promise for the production of pharmaceutically important cholestenone.  相似文献   

17.
The commonly used beverage and psychostimulant caffeine is known to inhibit human acetylcholinesterase enzyme. This pharmacological activity of caffeine is partly responsible for its cognition enhancing properties. However, the exact mechanisms of its binding to human cholinesterases (acetyl and butyrylcholinesterase; hAChE and hBuChE) are not well known. In this study, we investigated the cholinesterase inhibition by the xanthine derivatives caffeine, pentoxifylline, and propentofylline. Among them, propentofylline was the most potent AChE inhibitor (hAChE IC50 = 6.40 μM). The hAChE inhibitory potency was of the order: caffeine (hAChE IC50 = 7.25 μM) < pentoxifylline (hAChE IC50 = 6.60 μM) ? propentofylline (hAChE IC50 = 6.40 μM). These compounds were less potent relative to the reference agent donepezil (hAChE IC50 = 0.04 μM). Moreover, they all exhibited selective inhibition of hAChE with no inhibition of hBuChE (IC50 > 50 μM) relative to the reference agent donepezil (hBuChE IC50 = 13.60 μM). Molecular modeling investigations indicate that caffeine binds primarily in the catalytic site (Ser203, Glu334 and His447) region of hAChE whereas pentoxifylline and propentofylline are able to bind to both the catalytic site and peripheral anionic site due to their increased bulk/size, thereby exhibiting superior AChE inhibition relative to caffeine. In contrast, their lack of hBuChE inhibition is due to a larger binding site and lack of key aromatic amino acids. In summary, our study has important implications in the development of novel caffeine derivatives as selective AChE inhibitors with potential application as cognitive enhancers and to treat various forms of dementia.  相似文献   

18.
A biocatalyst with high activity retention of lipase was fabricated by the covalent immobilization of Candida rugosa lipase on a cellulose nanofiber membrane. This nanofiber membrane was composed of nonwoven fibers with 200 nm nominal fiber diameter. It was prepared by electrospinning of cellulose acetate (CA) and then modified with alkaline hydrolysis to convert the nanofiber surface into regenerated cellulose (RC). The nanofiber membrane was further oxidized by NaIO4. Aldehyde groups were simultaneously generated on the nanofiber surface for coupling with lipase. Response surface methodology (RSM) was applied to model and optimize the modification conditions, namely NaIO4 content (2–10 mg/mL), reaction time (2–10 h), reaction temperature (25–35 °C) and reaction pH (5.5–6.5). Well-correlating models were established for the residual activity of the immobilized enzyme (R2 = 0.9228 and 0.8950). We found an enzymatic activity of 29.6 U/g of the biocatalyst was obtained with optimum operational conditions. The immobilized lipase exhibited significantly higher thermal stability and durability than equivalent free enzyme.  相似文献   

19.
A novel method was developed for the immobilization of glucoamylase from Aspergillus niger. The enzyme was immobilized onto polyglutaraldehyde-activated gelatin particles in the presence of polyethylene glycol and soluble gelatin, resulting in 85% immobilization yield. The immobilized enzyme has been fully active for 30 days. In addition, the immobilized enzyme retained 90 and 75% of its activity in 60 and 90 days, respectively. The enzyme optimum conditions were not affected by immobilization and the optimum pH and temperature for free and immobilized enzyme were 4 and 65 °C, respectively. The kinetic parameters for the hydrolysis of maltodextrin by free and immobilized glucoamylase were also determined. The Km values for free and immobilized enzyme were 7.5 and 10.1 g maltodextrin/l, respectively. The Vmax values for free and immobilized enzyme were estimated as 20 and 16 μmol glucose/(min μl enzyme), respectively. The newly developed method is simple yet effective and could be used for the immobilization of some other enzymes.  相似文献   

20.
《Process Biochemistry》2014,49(8):1304-1313
Pseudomonas cepacia lipase (PCL) was immobilized on ternary blend biodegradable polymer made up of polylactic acid (PLA), chitosan (CH), and polyvinyl alcohol (PVA). Immobilized biocatalyst was characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), % water content, protein and lipase activity assay. The lipase activity assay showed enhanced activity of immobilized lipase than crude lipase. Higher half life time (t1/2) and lower deactivation rate constant (Kd) was found for the n-hexane among various tested solvent. Influence of various reaction parameters on enzyme activity were studied in detail. When geraniol (1 mmol) and vinyl acetate (4 mmol) in toluene (3 mL) were reacted with 50 mg immobilized lipase at 55 °C; then 99% geraniol was converted to geranyl acetate after 3 h. Various kinetic parameters such as rmax, Ki(A), Km(A), Km(B) were determined using non-linear regression analysis for ternary-complex and Bi–Bi ping-pong mechanism. The kinetic study showed that reaction followed ternary-complex mechanism with inhibition by geraniol. Activation energy (Ea) was found to be lower for immobilized lipase (13.76 kCal/mol) than crude lipase (19.9 kCal/mol) indicating better catalytic efficiency of immobilized lipase. Immobilized biocatalyst demonstrated 4 fold increased catalytic activity than crude lipase and recycled five times.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号