Functional stabilization of trypsin by conjugation with beta-cyclodextrin-modified carboxymethylcellulose

Bovine pancreatic trypsin was chemically modified by a beta-cyclodextrin-carboxymethylcellulose polymer using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide as coupling agent. The conjugate retained 110% and 95% of the initial esterolytic and proteolytic activity, respectively, and contained about 2 mol of polymer per mol of trypsin. The optimum temperature for trypsin was increased to 8 degrees C after conjugation. The thermostability of the enzyme was increased to about 16 degrees C after modification. The conjugate prepared was also more stable against thermal incubation at different temperatures ranging from 45 degrees C to 60 degrees C. In comparison with native trypsin, the polymer-enzyme complex was more resistant to autolytic degradation at pH 9.0, retaining about 65% of the initial activity after 3h incubation. In addition, modification protected trypsin against denaturation in the presence of sodium dodecylsulfate.     

Purification and characterization of inducible cephalexin synthesizing enzyme in Gluconobacter oxydans

Cephalexin synthesizing enzyme (CSE) of Gluconobacter oxydans ATCC 9324 was purified up to about 940-fold at a yield of 12%. CSE biosynthesis in G. oxydans was found inducible in the presence of D-phenylglycine but not its substrate phenylglycine methyl ester. The purified enzyme was shown homogeneous on SDS-PAGE and exhibited a specific activity of 440 U per mg protein. The apparent molecular mass of the native enzyme was estimated to be 70 kDa over a Superdex 200 gel filtration column and 68 kDa on SDS-PAGE, indicating that the native enzyme is a monomer. Its isoelectric focusing point is 7.1, indicating a neutral character. The enzyme had maximal activity around pH 6.0 to 6.5, and this activity was thermally stable up to 40 degrees C. Synthesis of cephalexin from D-phenylglycine methyl ester and 7-amino-3-deacetoxycephalosporanic acid (7-ADCA) by the purified CSE was demonstrated. Its L-enantiomer was not accepted by CSE. Apart from cephalexin, ampicillin was also synthesized by the purified CSE from its acyl precursors and 6-aminopenicillanic acid (6-APA). Substrate specificity studies indicated that the enzyme required a free alpha amino group and an activated carboxyl group as a methyl ester of D-form phenylglycine. Interestingly, the purified enzyme did not catalyze hydrolysis of its products, e.g., cephalexin, cephradine, and ampicillin, in contrast to enzymes from other strains of Pseudomonadaceae.     

Rat mammary-gland fatty acid synthase. A simple purification procedure and stoicheiometry of CoA ester binding.

A simple procedure was devised which allows purification of rat lactating-mammary-gland fatty acid synthase to a high degree of purity, with recoveries of activity exceeding 50%. Over 50 mg of enzyme was isolated from 60 g of mammary tissue. The specific activity of the purified enzyme was about 2.5 mumol of NADPH oxidized/min per mg of protein at 37 degrees. The enzyme appeared homogeneous by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and by immunodiffusion analysis. Each mol (Mr 480 000) of the enzyme bound 3 mol of acetyl and 3-4 mol of malonyl groups when the binding experiments were performed at 0 degrees for 30 s. The presence of NADPH did not influence the binding stoicheiometry for these acyl-CoA derivatives. Approx. 2 mol of taurine was found per mol of the performic acid-oxidized enzyme, suggesting that there were 2 mol of 4'-phosphopantetheine in the native enzyme. Rat mammary-gland fatty acid synthase required free CoA for activity.     

Purification and partial characterization of a cellodextrin glucohydrolase (beta-glucosidase) from Trichoderma reesei strain QM 9414

A beta-glucosidase (E.C. 3.2.1.21) was isolated from the culture filtrate of fungus Trichoderma reesei QM 9414 grown in continuous culture with biomass retention. The crude extracellular enzyme preparation was fractionated by a three-step purification procedure [chromatography on Fractogel HW-55 (S) and Bio-Gel A 0.5 plus final preparative isoelectric focusing] to yield three beta-glucosidases with isoelectric points at pH 8.4, 8.0, and 7.4. Only one enzyme (pi 8.4) met the stringent criterion of being homogeneous according to titration curve analysis. This enzyme was then characterized not to be a glycoprotein, although the native protein contained 35% carbohydrate (as glucose). It was found to have an apparent molar mass of 7 x 10(4) g/mol (SDS-PAGE), exhibited its optimum activity towards cellobiose at pH 4.5 and 70 degrees C (30 min test), and lost less than 3% activity at 50 degrees C over a period of 7 h. The K(M) values towards cellobiose and p-nitrophenyl-beta-D-glucopyranoside were determined to be 0.5mM and 0.3mM, respectively. The enzyme hydrolyzed cellodextrins (cellotriose to cellooctaose) by sequentially splitting off glucose units from the nonreducing end of the oligomers. The extent of the observed transfer reactions varied with the initial substrate concentration. No enzyme activity towards microcrystalline cellulose or carboxymethylcellulose could be detected. The classification of the enzyme as beta-glucosidase or exo-beta-1,4-glucan glucohydrolase is discussed with respect to the exhibited hydrolytic activities.     

Effect of immobilization on stability and kinetic properties of alpha-L-fucosidase from Turbo cornutus

An amount of alpha-L-fucosidase from T. cornutus liver was copolymerized with glutaraldehyde using bovine serum albumin as the carrier protein. The properties of the native, the soluble enzyme polymer complex, and the insoluble enzyme polymer complex were studied and compared under various conditions of pH, temperature, substrate, and inhibitor concentration. Native alpha-L-fucosidase was heat labile and lost more than 85% of its activity when incubated at 55 degrees C for 5 min. In contrast, under equivalent incubation conditions, both the soluble and the insoluble enzyme polymer complexes exhibited enhanced resistance to thermal inactivation and after 5 min lost only 65 and 40% of their original activity, respectively. Polymerzation also resulted in the shift of pH optima towards the acidic range, a decrease in activation energy and a change in the apparent K(m) values towards the p-nitrophenyl-alpha-L-fucopyranoside substrate.     

Purification and characterization of an endoglucanase (1,4-beta-D-glucan glucanohydrolase) from Clostridium thermocellum.

An endoglucanase (1,4-beta-D-glucan glucanohydrolase, EC 3.2.1.4) was purified from Clostridium thermocellum by procedures that included centrifugation, ultrafiltration, selective precipitation, ion-exchange Sephadex chromatography and preparative gel electrophoresis. The 22-fold-purified enzyme behaved as a homogeneous protein under non-denaturing conditions. The enzyme represented a significant component (greater than 25%) of total extracellular endoglucanase activity, but was purified in low yield by the procedures employed. The native molecular weight of the endoglucanase was determined by ultracentrifugational analysis, amino acid composition and polyacrylamide-gel electrophoresis, and varied between 83000 and 94000. The enzyme contained 11.2% carbohydrate and was isoelectric at pH 6.72. The pH and temperature optima of the endoglucanase were 5.2 and 62 degrees C respectively. The enzyme lacked cysteine and was low in sulphur-containing amino acids. The purified endoglucanase displayed: high activity towards carboxymethylcellulose, celloheptaose, cellohexaose and cellopentaose; low activity towards Avicel microcrystalline cellulose and cellotetraose; no detectable activity towards cellotriose or cellobiose; increased activity towards cello-oligosaccharides with increasing degree of polymerization. The internal glycosidic bonds of cello-oligosaccharides were cleaved by the enzyme in preference to external linkages. The apparent Michaelis constant ([S]0.5V) and Vmax. for cellopentaose and cellohexaose hydrolysis were 2.30 mM and 39.3 mumol/min per mg of protein, and 0.56 mM and 58.7 mumol/min per mg of protein, respectively.     

Characterization and biotechnological application of an acid alpha-galactosidase from Tachigali multijuga Benth. seeds

Tachigali multijuga Benth. seeds were found to contain protein (364 mg g(-1)dwt), lipids (24 mg g(-1)dwt), ash (35 mg g(-1)dwt), and carbohydrates (577 mg g(-1)dwt). Sucrose, raffinose, and stachyose concentrations were 8.3, 3.0, and 11.6 mg g(-1)dwt, respectively. alpha-Galactosidase activity increased during seed germination and reached a maximum level at 108 h after seed imbibition. The alpha-galactosidase purified from germinating seeds had an M(r) of 38,000 and maximal activity at pH 5.0-5.5 and 50 degrees C. The enzyme was stable at 35 degrees C and 40 degrees C, but lost 79% of its activity after 30 min at 50 degrees C. The activation energy (E(a)) values for p-nitrophenyl-alpha-d-galactopyranoside (pNPGal) and raffinose were 13.86 and 4.75 kcal mol(-1), respectively. The K(m) values for pNPGal, melibiose, raffinose, and stachyose were 0.45, 5.37, 39.62 and 48.80 mM, respectively. The enzyme was sensitive to inhibition by HgCl(2), SDS, AgNO(3), CuSO(4), and melibiose. d-Galactose was a competitive inhibitor (K(i)=2.74 mM). In addition to its ability to hydrolyze raffinose and stachyose, the enzyme also hydrolyzed galactomannan.     

Preparation and properties of immobilized papain and lipase.

Papain and lipase were immobilized on derivatized Sepharose 4-B. The activated agarose had a binding capacity of 1.2 micronmol amino groups/ml packed agarose or 17 mg proteins/g dry agarose. The immobilized enzyme preparations were tested for the effects of pH of assay, temperature of assay, and substrate concentrations. The effect of 6M urea on the activity of papain was also determined. Soluble forms of the enzymes were used for comparison. Immobilization of the enzymes resulted in slightly different pH and temperature optima for activities. For immobilized papain Km(app) was similar to the one observed with soluble papain. Immobilization of lipase, however, cause a decrease in Km values. The immobilized enzyme preparations were stable when stored at 4 degrees C and pH 7.5 for periods up to eight months. The soluble enzymes lost their activity within 96 hr under similar storage conditions. Immobilized papain did not lose any activity after treatment with 6M urea for 270 min, whereas soluble papain lost 81% of its activity after the urea treatment, indicating that the immobilization of papain imparted structural and conformational stability to this enzyme.     

Interaction of lipoprotein lipase with subendothelial extracellular matrix

We have analyzed the binding of lipoprotein lipase (LPL) to the subendothelial extracellular matrix produced by cultured endothelial cells. Binding was linear up to a concentration of 0.5 microgram/ml (10 nM) enzyme used in this study, and equilibrium was achieved after 2 h of incubation with bovine 125I-LPL at 4 degrees C. Heparin and heparan sulfate effectively inhibited the binding of LPL to extracellular-matrix-coated plates; chondroitin sulfate had no effect, while high concentrations of dermatan sulfate or keratan sulfate inhibited binding of LPL to extracellular matrix by only 40%. Basic fibroblast growth factor (bFGF) did not affect LPL binding, while antithrombin-III (AT-III) caused up to a 50% inhibition of enzyme binding to extracellular matrix. alpha-Thrombin. 5.10(-6) M, and its esterolytically inactive derivative, DIP-alpha-thrombin, effectively inhibited binding of LPL to extracellular-matrix-coated plates. alpha-Thrombin was also able to release the extracellular-matrix-bound LPL in an active form. Extracellular-matrix-bound LPL detached into medium containing triolein emulsion and/or serum, and was catalytically active after being released. Extracellular-matrix-bound LPL lost 30% of its activity following incubation at 37 degrees C for 4 h. in contrast to soluble LPL which lost 75% of its activity. It is plausible to conclude from these data that in vivo the subendothelial basement membrane, similarly to extracellular matrix, sequesters and stabilizers LPL secreted into the subendothelial space by non-endothelial cells, and thus may play an important role in determining the route of LPL from its site of synthesis to its site of action.     

Collagenase of human skin basal cell epithelioma.

Collagenase of human basal cell epithelioma was purified by sequential ammonium sulfate precipitation, Sephadex gel filtration and affinity chromatography on collagen-polyacrylamide gel. The collagenase, when partially purified, was found to have an approximate molecular weight of 50,000. The purified enzyme contained no caseinolytic activity. On polyacrylamide gel electrophoresis, the purified enzyme gave a single protein band. The purified collagenase cleaved native acid-soluble guinea pig skin collagen at 37 degrees C with a pH optimum of 8. The enzyme was inhibited by EDTA, cysteine, and human serum but not by soybean trypsin inhibitor. Heparin did not stimulate the enzyme activity. Purified collagenase reduced the specific viscosity of native acid-soluble guinea pig skin collagen to 50 per cent of its original value at 27 degrees C. Polyacrylamide gel disc electrophoresis of the reaction products showed bands corresponding to alphaA, betaA, and alphaB fragments. Electron microscopic examination of SLS aggregates of the reaction products showed that the cleavage site by the enzyme was at a point 75 per cent from the "A" end (TCA75) and 25 per cent from the "B" end (TCB25) of the collagen molecule.     

Thermostable xylanase from Marasmius sp.: purification and characterization

We have screened 766 strains of fungi from the BIOTEC Culture Collection (BCC) for xylanases working in extreme pH and/or high temperature conditions, the so-called extreme xylanases. From a total number of 32 strains producing extreme xylanases, the strain BCC7928, identified by using the internal transcribed spacer (ITS) sequence of rRNA to be a Marasmius sp., was chosen for further characterization because of its high xylanolytic activity at temperature as high as 90 degrees C. The crude enzyme possessed high thermostability and pH stability. Purification of this xylanase was carried out using an anion exchanger followed by hydrophobic interaction chromatography, yielding the enzyme with >90% homogeneity. The molecular mass of the enzyme was approximately 40 kDa. The purified enzyme retained broad working pH range of 4-8 and optimal temperature of 90 degrees C. When using xylan from birchwood as substrate, it exhibits Km and Vmax values of 2.6 +/- 0.6 mg/ml and 428 +/- 26 U/mg, respectively. The enzyme rapidly hydrolysed xylans from birchwood, beechwood, and exhibited lower activity on xylan from wheatbran, or celluloses from carboxymethylcellulose and Avicel. The purified enzyme was highly stable at temperature ranges from 50 to 70 degrees C. It retained 84% of its maximal activity after incubation in standard buffer containing 1% xylan substrate at 70 degrees C for 3 h. This thermostable xylanase should therefore be useful for several industrial applications, such as agricultural, food and biofuel.     

Heat and autoclave resistance of cell-spreading activity of vitronectin.

We have investigated the heat- and autoclave-resistant properties of the cell-spreading activity of vitronectin, a cell-spreading glycoprotein in animal blood plasma. Vitronectin heated at 100 degrees C for 10 min or autoclaved at 121 degrees C at 1.2 kg/cm2 for 20 min retained the same cell-spreading activity as native vitronectin. In contrast, fibronectin and type-I collagen treated in the same way lost their activity almost completely. GRGDSP remarkably inhibited the cell-spreading activity of native, heated and autoclaved vitronectins. GRGESP did not inhibit the activity of native vitronectin, but, unexpectedly, partially inhibited the activity of both heated and autoclaved vitronectins. In SDS-polyacrylamide gel analysis under reducing conditions, vitronectin heated at 100 degrees C migrated mainly as a monomer, but autoclaved vitronectin migrated at both the top and front of the gel instead of at the position of the monomer. The change in molecular size during the heat- and autoclave treatments was partially prevented by adding 10 mM dithiothreitol or 2% 2-mercaptoethanol to the protein solution.     

Studies on conformation of soluble and immobilized enzymes using differential scanning calorimetry. 2. Specific activity and thermal stability of enzymes bound weakly and strongly to Sepharose CL 4B

Ribonuclease A (EC 3.1.4.22) and alpha-chymotrypsin (EC 3.4.21.1) have been covalently coupled, by a varying number of bonds, to Sepharose CL 4B which was activated with different amounts of CNBr. Upon increasing the number (1-8) of points of attachment between the enzyme and the matrix, the specific activities of immobilized ribonuclease A relative to its soluble counterpart decreased from 60 to 15% while the amount of protein coupled increased from 5 to 37 mg per g of sucked gel. Differential scanning calorimetry was used to determine whether the immobilization caused any changes in the physicochemical properties of the enzyme. Ribonuclease A, weakly bound to the matrix, showed almost the same behavior as the soluble enzyme. By contrast strongly immobilized enzyme exhibited a higher transition temperature (by about 5 degrees C) and a broader endotherm. Similar results were found for alpha-chymotrypsin.     

The enzymatic conversion of L-histidine to urocanic acid by whole cells of Micrococcus luteus immobilized on carbodiimide activated carboxymethylcellulose.

Whole cells of Micrococcus luteus (formerly Sarcina lutea ATCC 9341) have been covalently linked to a carboxymethylcellulose support system, with the retention of histidine ammonia-lyase activity. The dependence of the rate of urocanic acid formation on pH, temperature, and added surfactant concentration was similar for the free and the immobilized cells. The immobilization procedure used is based on the carbodiimide activation of carboxymethylcellulose and has been optimized for the histidine ammonia-lyase activity of the immobilized cells on a given weight of cellulose. In a column reactor at 23 degrees C and superficial velocity of 0.044 cm/min, 5 g of cellulose with bound cells gave a 35% conversion of an L-histidine solution (0.25M, pH 9.0) to urocanic acid for 16 days of continuous operation. The scope of this carbodiimide assisted immobilization procedure has been investigated for a series of microorganisms and a variety of carboxylate functionalized supports.     

Purification and properties of Bacillus subtilis SA-22 endo-1, 4-beta-D-mannanase.

beta-mannanase (EC 3.2.1.78) from Bacillus subtilis SA-22 was purified successively by ammonium sulfate precipitation, hydroxyapatite chromatography, Sephadex G-75 gel filtration and DEAE-52 anion-exchange chromatography. Through these steps, the enzyme was concentrated 30.75-fold with a recovery rate of 23.43%, with a specific activity of 34780.56 u/mg. Molecular weight of the enzyme was determined to be 38 kD by SDS-PAGE and 34 kD by gel filtration. The results revealed that the optimal pH value for the enzyme was 6.5 and the optimal temperature was 70 degrees C. The enzyme is stable between pH 5 to 10. The enzyme remained most of its activity after a treatment of 4 h at 50 degrees C, but lost 25% of activity at 60 degrees C for 4 h, lost 50% of activity at 70 degrees C for 3 h. The enzyme activity was strongly inhibited by Hg2+. The Michaelis constants (Km) were measured as 11.30 mg/mL for locust bean gum and 4.76 mg/mL for konjac powder, while Vmax for these two polysaccharides were 188.68 (micromol x mL(-1) x min(-1)) and 114.94 (micromol x mL(-1) x min(-1)), respectively.     

Glycation improves the thermostability of trypsin and chymotrypsin

A novel glycation procedure, in vacuo glycation, was used to attach glucose covalently to the lysine residues of trypsin and chymotrypsin. Glycated trypsin and glycated chymotrypsin have greatly increased thermostability compared to the native enzymes. For example, glycated bovine trypsin, incubated at 50 degrees C and pH 8.0 for 3 h, retained more than 50% of its original activity whereas the native enzyme was inactivated under the same conditions. Similarly, after incubation at 50 degrees C and pH 8.0, glycated bovine chymotrypsin retained 45% of its original activity and the native enzyme was inactivated. Glycated porcine trypsin is exceptionally thermostable and could be used to digest native ribonuclease at 70 degrees C without the need for prior denaturation. The apparent increase in the thermal stability of the glycated proteins observed in activity measurements is also reflected by an increase in the T(m) values determined with differential scanning calorimetry (DSC) and circular dichroism (CD). The glycation does not alter the activity or specificity of these enzymes.     

Immobilization of dextransucrase from Leuconostoc mesenteroides NRRL B-512F on Eupergit C supports

Dextransucrase from Leuconostoc mesenteroides B-512F was immobilized on epoxy-activated acrylic polymers with different textural properties (Eupergit C and Eupergit C 250L). Prior to immobilization, dextransucrase was treated with dextranase to remove the dextran layer covering the enzyme surface, thus increasing the accessibility of its reactive groups to the epoxide centers of the support. Elimination of 99% of the initial carbohydrate content was determined by the anthrone method. To prevent enzyme inactivation, the immobilization was carried out at pH 5.4, at which the coupling to the support took place through the carboxylic groups of the enzyme. The effects of the amount (mg) of dextransucrase added per gram of support (from 0.2:1 to 30:1), temperature and contact time were studied. Maximum activity recovery of 22% was achieved using Eupergit C 250L. Using this macroporous support, the maximum specific activity (710 U/g biocatalyst) was significantly higher than that obtained with the less porous Eupergit C (226 U/g biocatalyst). The dextransucrase immobilized on Eupergit C 250L showed similar optimal temperature (30 degrees C) and pH (5-6) compared with the native enzyme. In contrast, a notable stabilization effect at 30 degrees C was observed as a consequence of immobilization. After a fast partial inactivation, the dextransucrase immobilized on Eupergit C 250L maintained more than 40% of the initial activity over the following 2 days. The features of this immobilized system are very attractive for its application in batch and fixed-bed bioreactors.     

Enzyme immobilization using a cellulose-binding domain: properties of a beta-glucosidase fusion protein.

Using molecular genetic techniques, a fusion protein has been produced which contains the cellulose-binding domain (CBD) of an exoglucanase (Cex) from Cellulomonas fimi fused to a beta-glucosidase (Abg) from Agrobacterium sp. The CBD functions as an affinity tag for the simultaneous purification and immobilization of the enzyme on cellulose. Binding to cellulose was stable for prolonged periods at temperatures from 4 degrees C to at least 50 degrees C, at ionic strengths from 10 mM to greater than 1 M, and at pH values below 8. The fusion protein can be desorbed from cellulose with distilled water or at pH greater than 8. Immobilized enzyme columns of the fusion protein bound to cotton fibers exhibited stable beta-glucosidase activity for at least 10 days of continuous operation at temperatures up to 37 degrees C. At higher temperatures, the bound enzyme lost activity. The thermal stability of the fusion protein was greatly improved by immobilization. Immobilization did not alter the pH stability. Except for its ability to bind to cellulose, the properties of the fusion protein were virtually the same as those of the native enzyme.     

Enzymatic hydrolysis of organophosphate insecticides, a possible pesticide disposal method.

A crude cell extract from a mixed bacterial culture growing on parathion, an organophosphate insecticide, hydrolyzed parathion (21 C) at a rate of 416 nmol/min per mg of protein. This rate of enzymatic hydrolysis, when compared with chemical hydrolysis by 0.1 N sodium hydroxide at 40 C, was 2, 450 times faster. Eight of 12 commonly used organophosphate insecticides were enzymatically hydrolyzed with this enzyme preparation at rates ranging from 12 to 1,360 nmol/min per mg of protein. Seven pesticides were hydrolyzed at rates significantly higher (40 to 1,005 times faster) than chemical hydrolysis. The pH optimum for enzymatic hydrolysis of the eight pesticides ranged from 8.5 to 9.5, with less than 50% of maximal activity expressed at pH 7.0. Maximal enzyme activity occurred at 35 C. The crude extract lost its activity at the rate of only 0.75%/day when stored at 6 C. Eight organic solvents, ranging from methanol to hexane, at low concentrations stimulated enzymatic hydrolysis by 3 to 20%, whereas at higher concentrations (1,000 mg/liter) they inhibited the reaction (9 to 50%). Parathion metabolites p-nitrophenol, hydroquinone, and diethylthiophosphoric acid, at up to 100-mg/liter concentrations, did not significantly influence enzyme activity.     

Hydrolysis of rice hull by crosslinked Aspergillus niger cellulase

A. niger cellulase was crosslinked by glutaraldehyde to obtain a heat-stable enzyme preparation for rice hull cellulose hydrolysis. Under optimized crosslinking conditions of 0.12 M glutaraldehyde, pH 7.0, temperature 40 degrees C and at 45 min of crosslinking, a preparation having 15% more activity than free enzyme was obtained which also had considerable improvement in heat stability at 65 degrees C and 70 degrees C. Whereas the free enzyme lost 80% of its activity in 4 h at 65 degrees C, the crosslinked preparation lost only 30% activity. The crosslinked preparation hydrolyzed cellulosic biomass more effectively giving 2.2 mg/ml glucose and 52% corresponding saccharification in 4 h at 65 degrees C as compared to 14% saccharification by free enzyme under similar conditions.