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1.
Abstract

Purified Acetobacter tropicalis dextransucrase was immobilized in different matrices viz. calcium-alginate, κ-carrageenan, agar, agarose and polyacrylamide. Calcium-alginate was proved to be superior to the other matrices for immobilization of dextransucrase enzyme. Standardization of immobilization conditions in calcium-alginate resulted in 99.5% relative activity of dextransucrase. This is the first report with such a large amount of relative activity as compared to the previous reports. The immobilized enzyme retained activity for 11 batch reactions without a decrease in activity which suggested that enzyme can be used repetitively for 11 cycles. The dextransucrase was also characterized, which revealed that enzyme worked best at pH 5.5 and 37?°C for 30?min in both the free as well as immobilized state. Calcium-alginate immobilized dextransucrase of A. tropicalis showed the Km and Vmax values of 29?mM and 5000?U/mg, respectively. Free and immobilized enzyme produced 5.7?mg/mL and 2.6?mg/mL of dextran in 2?L bench scale fermenter under optimum reaction conditions. This immobilization method is very unconventional for purified large molecular weight dextran-free dextransucrase of A. tropicalis as this method is used usually for cells. Such reports on entrapment of purified enzyme are rarely documented.  相似文献   

2.
The dextransucrase gene from Weissella confusa Cab3, having an open reading frame of 4.2?kb coding for 1,402?amino acids, was amplified, cloned, and expressed in Lactococcus lactis. The recombinant dextransucrase, WcCab3-rDSR was expressed as extracellular enzyme in M17 medium with a specific activity of 1.5?U/mg which after purification by PEG-400 fractionation gave 6.1?U/mg resulting in 4-fold purification. WcCab3-rDSR was expressed as soluble and homogeneous protein of molecular mass, approximately, 180?kDa as analyzed by SDS-PAGE. It displayed maximum enzyme activity at 35°C at pH 5.0 in 50?mM sodium acetate buffer. WcCab3-rDSR gave Km of 6.2?mM and Vm of 6.3?µmol/min/mg. The characterization of dextran synthesized by WcCab3-rDSR by Fourier transform infrared and nuclear magnetic resonance spectroscopic analyses revealed the structural similarities with the dextran produced by the native dextransucrase. The modeled structure of WcCab3-rDSR using the crystal structures of dextransucrase from Lactobacillus reuteri (protein data bank, PDB id: 3HZ3) and Streptococcus mutans (PDB id: 3AIB) as templates depicted the presence of different domains such as A, B, C, IV, and V. The domains A and B are circularly permuted in nature having (β/α)8 triose phosphate isomerase-barrel fold making the catalytic core of WcCab3-rDSR. The structure superposition and multiple sequence alignment analyses of WcCab3-rDSR with available structures of enzymes from family 70 GH suggested that the amino acid residue Asp510 acts as a nucleophile, Glu548 acts as a catalytic acid/base, whereas Asp621 acts as a transition-state stabilizer and these residues are found to be conserved within the family.  相似文献   

3.
Aspergillus niger β-xylosidase was characterized when in soluble form and when immobilized to alkylamine porous silica with glutaraldehyde and to alumina with titanium tetrachloride. Energies of activation averaged 13.4 KcaL/mol for the soluble enzyme, 9.0 Kcal/mol when immobilized to alumina, and 8.0 Kcal/mol when bound to silica. The highest activity of all forms of β-xylosidase was found near pH 3. The soluble enzyme was highly stable at pH 4, where lowest rates of decay occurred, and temperature of 65°C and below. The decay rates of alumina-bound β-xylosidase and pH 4 and equivalent temperatures were approximately 10 times as high. Michaells constants were 0.200 and 0.262mM for o-nitrophenyl-β-D -xylopyranoside with soluble and alumina-bound β-xylosidase, respectively.  相似文献   

4.
The (Na++K+)-activated, Mg2+-dependent ATPase from rabbit kidney outer medulla was prepared in a partially inactivated, soluble from depleted of endogenous phospholipids, using deoxycholate. This preparation was reactivated 10 to 50-fold by sonicated liposomes of phosphatidylserine, but not by non-sonicated phosphatidylserine liposomes or sonicated phosphatidylcholine liposomes. The reconstituted enzyme resembled native membrane preparations of (Na++K+)-ATPase in its pH optimum being around 7.0 showing optimal activity at Mg2+: ATP mol ratios of approximately 1 and a Km value for ATP of 0.4 mM.Arrhenius plots of this reactivated activity at a constant pH of 7.0 and an Mg2+: ATP mol ratio of 1:1 showed a discontinuity (sharp change of slope) at 17 °C, With activation energy (Ea) values of 13–15 kcal/mol above this temperature and 30–35 kcal below it. A further discontinuity was also found at 8.0 °C and the Ea below this was very high (> 100 kcal/mol).Incresed Mg2+ concentrations at Mg2+: ATP ratios in excess of 1:1 inhibited the (Na++K+)-ATPase activity and also abolished the discontinuities in the Arrhenius plots.The addition of cholesterol to phosphatidylserine at a 1:1 mol ratio partially inhibited (Na++K+)-ATPase reactivation. Arrhenius plots under these conditions showed a single discontinuity at 20°C and Ea values of 22 and 68kcal/mol above and below this temperature respectively. The ouabain-insensitive Mg2+-ATPase normally showed a linear Arrhenius plot with an Ea of 8 kcal/mol. The cholesterol-phosphatidylserine mixed liposomes stimulated the Mg2+-ATPase activity, which now also showed a discontinuity at 20 °C with, however, an increased value of 14 kcal/mol above this temperature and 6 kcal/mol below. Kinetic studies showed that cholesterol had no significant effect on the Km for ATP.Since both of cholesterol and Mg2+ are know to alter the effects of temperature on the fluidity of phospholipids the above result are discussed in this context.  相似文献   

5.
Abstract Salt-stimulated ATPase activity in membrane preparations obtained from roots of Atriplex nummularia Lindl. at pH 5 was not suscep-tible to inhibition by KC1 or NaCl up to 450 mol m-3 but showed a broad peak of activity between 150 and 300 mol m?3. At pH 8 stimulation occurred at 50 mol m?3 but concentrations above 100 mol m?3 depressed activity below the level of the MgATPase activity. By contrast, preparations from roots of Pisum sativum L. at pH 5 showed maximal stimulation at 25 to 50 mol m?3 of NaCl or KC1; concentrations higher than 150 mol m?3 depressed activity below that of MgATPase activity. At pH 8 maximal stimulation was observed at 5 to 10 mol m?3 NaCl or KC1 while the threshold for inhibition was reduced to 15 mol m?3. With increasing salt concentrations the pH profiles for NaCl stimulation of Atriplex ATPase activity (expressed as the difference between treatment and control) showed a progressive displacement of the apparent optimum towards lower pH. The shift was not apparent when stimulation was expressed as a percentage of MgATPase activity. This shift may be accounted for if NaCl stimulated the monovalent salt-activated ATPase activity but simultaneously inhibited MgATPase activity.  相似文献   

6.
An extracellular thermostable alkaline serine protease enzyme from Aeribacillus pallidus C10 (GenBank No: KC333049), was purified 4.85 and 17. 32-fold with a yield of 26.9 and 19.56%, respectively, through DE52 anion exchange and Probond affinity chromatography. The molecular mass of the enzyme was determined through sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), with approximately 38.35?kDa. The enzyme exhibited optimum activity at pH 9 and at temperature 60?°C. It was determined that the enzyme had remained stable at the range of pH 7.0–10.0, and that it had preserved more than 80% of its activity at a broad temperature range (20–80?°C). The enzyme activity was found to retain more than 70% and 55% in the presence of organic solvents and commercial detergents, respectively. In addition, it was observed that the enzyme activity had increased in the presence of 5% SDS. KM and Vmax values were calculated as 0.197?mg/mL and 7.29?μmol.mL?1.min?1, respectively.  相似文献   

7.
Phenol oxidase (EC 1.14.18.1) from the microscopic fungusMycelia sterilia IBR 35219/2 was immobilized using glutaraldehyde on macroporous silica carriers. The enzyme immobilized on amino-Silochrome SKh-2 or aminopropyl-Silochrome 350/80 exhibited maximum activity. Soluble and immobilized phenol oxidases were compared. Compared to the soluble enzyme, the activity of which was optimum at pH 5.5, immobilized phenol oxidase exhibited optimum activity under slightly more acidic conditions (pH 5.2). Immobilization considerably increased enzyme stability. Both soluble and immobilized forms of phenol oxidase fromM. sterilia IBR 35 219/2 catalyze oxidative conversion of phenolic compounds of green tea extract.  相似文献   

8.
The use of heterogeneous biocatalysis in industrial applications is advantageous and the enzyme stability improvement is a continuous challenge. Therefore, we designed β‐galactosidase heterogeneous biocatalysts by immobilization, involving the support synthesis and enzyme selection (from Bacillus circulans, Kluyveromyces lactis, and Aspergillus oryzae). The underivatized, tailored, macro‐mesoporous silica exhibited high surface area, offered high enzyme immobilization yields and activity. Its chemical activation with glyoxyl groups bound the enzyme covalently, which suppressed lixiviation and conferred higher pH and thermal stability (120‐fold than for the soluble enzyme), without observable reduction of activity/stability due to the presence of silica. The best balance between the immobilization yield (68%), activity (48%), and stability was achieved for Bacillus circulans β‐galactosidase immobilized on glyoxyl‐activated silica, without using stabilizing agents or modifying the enzyme. The enzyme stabilization after immobilization in glyoxyl‐activated silica was similar to that observed in macroporous agarose‐glyoxyl support, with the reported microbiological and mechanical advantages of inorganic supports. The whey lactolysis at pH 6.0 and 25°C by using this catalyst (1 mg ml?1, 290 UI g?1) was still 90%, even after 10 cycles of 10 min, in batch process but it could be also implemented on continuous processes at industrial level with similar results.  相似文献   

9.
The industrial Leuconostoc strain B/110-1-2 producing dextran and dextran derivatives was taxonomically identified by 16S rRNA as L. citreum. Its dextransucrase enzymes were characterized according to their cellular location and reaction specificity. In the presence of sucrose, the strain B/110-1-2 produced two cell-associated dextransucrases (31.54% of the total glucosyltransferase activity) with molecular weights of 160 and 240 kDa and a soluble dextransucrase (68.46%) at 160–180 kDa. Two open reading frames (ORF) coding for L. citreum strain B/110-1-2 dextransucrases were identified. One of them shared a 52% identity with the alternansucrase ASR of L. citreum NRRL B-1355 and with a putative annotated alternansucrase sequence found in the genome of L. citreum KM20. The structural analysis (HPAEC-PAD, HPSEC, and 13C-NMR) of the polymer and oligodextrans produced by the B/110-1-2 dextransucrases suggest this novel glucansucrase has specificity similar to a dextransucrase but not to an alternansucrase, producing a soluble linear dextran with glucose molecules linked mainly in α-1,6 and α-1,3 with α-1,4 branches. These results enhance the understanding of this industrially significant strain and will aid in distinguishing between physiologically similar Leuconostoc spp. strains.  相似文献   

10.
Phosphatidylinositol-specific phospholipase C was purified from the soluble fraction of suspension-cultured rice cells. The apparent molecular weight of rice enzyme was estimated to be 50,000 by both Sephadex G-100 gel filtration and SDS–polyacrylamide gel electrophoresis, indicating that the enzyme is composed of a single polypeptide. The enzyme had an isoelectric point of 6.3. The soluble phospholipase C had a high degree of specificity toward phosphatidylinositol and a weak activity toward phosphatidyl-inositol monophosphate, while the enzyme did not hydrolyze the other phospholipids or p-nitrophenylphosphorylcholine. Vmax and Km values were 5.0, μmol/min/mg protein and 0.3 mM, respectively. The pH dependency of the enzyme activity was sharp with an optimum of 5.2. In addition, the phospholipase C was a Ca2+ -dependent enzyme. The marked activation of enzyme was observed in the presence of 10 to 250, μM Ca2+ and higher Ca 2+ concentrations than 1 mM had a strong inhibitory effect. A possible regulation of the phospholipase C activity by pH and Ca2+ concentrations in the rice cells is discussed.  相似文献   

11.
Summary Xylanase from Scytalidium thermophilum was immobilized on Eudragit L-100, a pH sensitive copolymer of methacrylic acid and methyl methacrylate. The enzyme was non-covalently immobilized and the system expressed 70% xylanase activity. The immobilized preparation had broader optimum temperature of activity between 55 and 65 °C as compared to 65 °C in case of free enzyme and broader optimum pH between 6.0 and 7.0 as compared to 6.5 in case of free enzyme. Immobilization increased the t1/2 of enzyme at 60 °C from 15 to 30 min with a stabilization factor of 2. The Km and Vmax values for the immobilized and free xylanase were 0.5% xylan and 0.89 μmol/ml/min and 0.35% xylan and 1.01 μmol/ml/min respectively. An Arrhenius plot showed an increased value of activation energy for immobilized xylanase (227 kcal/mol) as compared to free xylanase (210 kcal/mol) confirming the higher temperature stability of the free enzyme. Enzymatic saccharification of xylan was also improved by xylanase immobilization.  相似文献   

12.
The standard Gibbs free energy change of hydrolysis of α-d-ribose 1-phosphate has been measured at pH 7.0, ionic strength 0.1 m, and 25 °C by combining the corresponding values of the two following reactions: adenosine + H2O ág adenine + ribose (ΔG0′ = ?2.3 ± 0.1 kcal/mol), catalyzed by adenosine nucleosidase, and ribose 1-phosphate + adenine ág adenosine + PiG0′ = ?3.1 ± 0.1 kcal/mol), catalyzed by adenosine phosphorylase. The standard Gibbs free energy changes were calculated for both reactions from the equilibrium constant. A value of -5.4 ± 0.15 kcal/mol, comparable to that of other hemiacetal phosphoric esters, was obtained for the hydrolysis of ribose 1-phosphate.  相似文献   

13.
Abstract

Truffles are symbiotic hypogeous edible fungi (form of mushroom) that form filamentous mycelia in their initial phase of the growth cycle as well as a symbiotic association with host plant roots. In the present study, Tuber maculatum mycelia were isolated and tested for extracellular amylase production at different pH on solid agar medium. Furthermore, the mycelium was subjected to submerged fermentation for amylase production under different culture conditions such as variable carbon sources and their concentrations, initial medium pH, and incubation time. The optimized conditions after the experiments included soluble starch (0.5% w/v), initial medium pH of 7.0, and incubation time of 7 days, at room temperature (22?±?2?°C) under static conditions which resulted in 1.41?U/mL of amylase. The amylase thus obtained was further characterized for its biocatalytic properties and found to have an optimum activity at pH 5.0 and a temperature of 50?°C. The enzyme showed good thermostability at 50?°C by retaining 98% of the maximal activity after 100?min of incubation. The amylase activity was marginally enhanced in presence of Cu2+ and Na+ and slightly reduced by K+, Ca2+, Fe2+, Mg2+, Co2+, Zn2+, and Mn2+ ions at 1?mM concentration.  相似文献   

14.
A glucoamylase was purified from the culture broth of Paecilomyces varioti AHU 9417 by precipitation with ethanol, chromatography on DEAE-Sepharose CL-6B, gel filtration on Bio-Gel P-150, and preparative disc electrophoresis. The enzyme was homogeneous by disc electrophoretic analysis. The molecular weight was estimated to be 6.9×104 by SDS-disc electrophoresis, and the optimum pH was 4.5. The enzyme preferentially hydrolyzes α-1,4-glucosidic linkages in a series of maltooligosaccharides, and is capable to slowly hydrolyzing nigerose, isomaltose, and panose, but is not active on kojibriose. Soluble starch, amylopectin, glycogen, and β-limit dextrin are rapidly degraded. Activity toward raw starches is very low, but rice and waxy corn raw starches are relatively subject to attack. The subsite affinities (Ai) of each subsite (i) in the active site of the enzyme were evaluated from the Michaelis constants (Km) and the molecular activities (k0) for a series of maltooligosaccharides according to the subsite theory. The active site was considered to be made up of about four subsites: A1?0.46 kcal/mol, A2?4.78 kcal/mol, A3?1.76 kcal/mol and A4?0.67 kcal/mol.  相似文献   

15.
Carbonic anhydrase (CA) catalyzes the reversible reaction of hydration of CO2 to bicarbonate and the dehydration of bicarbonate back to CO2. Sequestration of CO2 from industrial processes or breathing air may require a large amount of highly active and stable CA. Therefore, the objectives of the present study were to purify large amounts of CA from a cheap and easily accessible source of the enzyme and to characterize the enzymatic and kinetic properties of soluble and immobilized enzyme. We recovered 80% of pure enzyme with a specific activity of 4870 EU/mg protein in a single step using sheep blood lysates from slaughter house waste products and CA specific inhibitor affinity chromatography. Since affinity pure CA showed both anhydrase and esterase activities, we measured the esterase activities for enzymology. The Michaelis–Menten constant, KM, pH optimum, activation energy, and thermal stability of soluble enzymes were 8 × 10?2 M, 7.3 pH, 7.3 kcal/mol and 70 °C, respectively.The immobilization of the enzyme to Affigel-10 was very efficient and 83% of purified enzyme was immobilized. The immobilized enzyme showed a KM of 5 × 10?2 M and activation energy of 8.9 kcal/mol, suggesting a better preference of substrate for immobilized enzyme in comparison to soluble enzyme. In contrast to soluble enzyme, immobilized enzyme showed relatively higher activity at pH 6–8. From these results, we concluded that a shift in pH profile toward acidic pH is due to modification of lysine residues involved in the immobilization process. The immobilized enzyme was stable at higher temperatures and showed highest activity at 80 °C. The activity of immobilized enzyme in a flow reactor at 0.5–2.2 ml/min flow rate was unaffected. Collectively, results from the present study suggested the application of blood lysate waste from animal slaughterhouses for purification of homogeneous enzyme for CO2 capture in a flow reactor.  相似文献   

16.
By using optical rotatory dispersion measurements, the helix content of poly Glu50Lys50 has been investigated and compared with that of poly Glu20Lys20Ala60 in aqueous solutions. Measurements were made at pH 3 and at pH 8 in various concentrations of lithium bromide. Various factors affecting helix stabilization are considered and their perturbation by lithium bromide is related to the shape of the observed transition curves. A residual helix content of 12% in 8M LiBr, based upon a b0 of +100 for a fully random conformation, was observed for poly Glu50Lys50 at pH 3 and 8. The loss of helix content of poly Glu50Lys50 as a function of temperature is also reported. ΔH is approximately ?6.9 kcal./mole for the overall transition, compared to ?6.5 kcal./mole for poly Glu20Lys20Ala60. The midpoint of the broad transition is near 40°C. at pH 3, but much lower, at ?10 to 0°C., at pH 8. These results are discussed in terms of the stabilizing factors for the partial helix content of the polypeptides.  相似文献   

17.
Simultaneous curve fitting for the ionization parameters of oxidized and reduced horse heart cytochrome c in 0.15M KCl and 20°C yields values for the ionization constants (as pK′) and the heats of ionization (ΔHi) which can reconstruct either the potentiometric or thermal titration curves. Reduced cytochrome c requires 8 sets of groups, whereas oxidized cytochrome c requires 10 sets of groups. The additional groups in the oxidized preparation appear to involve the ferriheme (pK′, 9.25; ΔHi, 13.7 kcal/mol) and a tyrosine (pK′ ? 10.24) that is not present in the reduced form. The potentiometric and thermal difference curves (reduced – oxidized) involve the appearance of 17 kcal/mol centered at pH 9.7 and 5.8 kcal/mol centered at pH 4.9. The carboxyl groups in both species appear to be normal for the hydrogen-bonded form. Only one histidine has normal ionization properties (pK′, 6.7; ΔHi, 7.5 kcal/mol), as do 17 of the lysine residues (pK′, 10.8; ΔHi, 11.5 kcal/mol).  相似文献   

18.
A method for isolating extracellular glucose oxidase from the fungus Penicillium funiculosum 46.1 using ultrafiltration membranes was developed. Two samples of the enzyme with a specific activity of 914–956 IU were obtained. The enzyme exhibited a high catalytic activity at pH above 6.0. The effective rate constant of glucose oxidase inactivation at pH 2.6 and 16°C was 2.74 × 10–6 s–1. This constant decreased significantly as the pH of the medium increased (4.0–10.0). The temperature optimum for glucose oxidase–catalyzed -D-glucose oxidation was in the range 30–65°C. At temperatures below 30°C, the activation energy for -D-glucose oxidation was 6.42 kcal/mol; at higher temperatures, this parameter was equal to 0.61 kcal/mol. Kinetic parameters of glucose oxidase–catalyzed -D-glucose oxidation depended on the initial concentration of the enzyme in the solution. Glucose oxidase also catalyzed the oxidation of 2-deoxy-D-glucose, maltose, and galactose.  相似文献   

19.
The reversible thermal unfolding of the archaeal histone-like protein Ssh10b from the extremophile Sulfolobus shibatae was studied using differential scanning calorimetry and circular dichroism spectroscopy. Analytical ultracentrifugation and gel filtration showed that Ssh10b is a stable dimer in the pH range 2.5–7.0. Thermal denaturation data fit into a two-state unfolding model, suggesting that the Ssh10 dimer unfolds as a single cooperative unit with a maximal melting temperature of 99.9 °C and an enthalpy change of 134 kcal/mol at pH 7.0. The heat capacity change upon unfolding determined from linear fits of the temperature dependence of ΔHcal is 2.55 kcal/(mol K). The low specific heat capacity change of 13 cal/(mol K residue) leads to a considerable flattening of the protein stability curve (ΔG (T)) and results in a maximal ΔG of only 9.5 kcal/mol at 320 K and a ΔG of only 6.0 kcal/mol at the optimal growth temperature of Sulfolobus.  相似文献   

20.
Abstract

Present study was undertaken to develop cross-linked enzyme aggregate (CLEA)of alkaline serine proteases (sp) from Pythium myriotylum (Pm), a necrotrophic oomycete reported to considerably secrete serine proteases. Among various precipitants screened for spPm1-CLEA preparation, ammonium sulfate at 80% saturation (w/v) yielded 100% activity recovery and retention of spherical morphology as observed by SEM analysis. Addition of glutaraldehyde as cross-linker at 1% (v/v) concentration with optimized ammonium sulfate concentration for 1?hour at 100?rpm yielded 100% activity recovery of spPm1-CLEA from 8-day old P. myriotylum culture filtrate. Addition of BSA (10?mg/ml) to CLEA cross-linking reaction mix reduced CLEA size from the range of 1.82–1.19?µm to 394–647?nm. spPm1-CLEA preparations retained 100% activity at temperature of 80?°C and pH 12.0 signifying their potential commercial applications. In terms of kinetic parameters, present process enhanced kinetic parameters as revealed by 1.67?U.mg?1 specific activity, Km of 0.062?mM and Vmax of 0.145?µmol.min?1.mg?1 for the spPm1-CLEA compared to 0.288?U.mg?1 specific activity, Km of 0.060?mM and Vmax of 0.20?µmol.min?1.mg?1 determined for the free spPm1 enzyme. Study has successfully demonstrated the concept of CLEA in enhancing spPm1 stability and the results so generated can be translated in future towards development of robust biocatalysts.  相似文献   

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