Immobilized enzymes in reverse micelles: studies with gel-entrapped trypsin and alpha-chymotrypsin in AOT reverse micelles

Trypsin and alpha-chymotrypsin were immobilized by gelentrapment in polyacrylamide cross-linked with N,N(1)-methylenebisacrylamide. The immobilized enzymes are catalytically efficient in suspensions of reverse micelles formed in isooctane by bis(2-ethylhexyl) sodium sulfosuccinate (AOT) and water. Both entrapped enzymes are stable in reverse micellar suspension at room temperature and pH 8.2 for 3 days and lose 30-40% activity after 1 week. The enzymes obey Michaelis-Menten kinetics in the investigated concentration range with K(m) values higher than those in solution. Activity of the enzymes is independent of the water content of the micellar solution. No shift in pH optimum was observed for immobilized trypsin activity toward Nalpha-benzoyl-L-arginine ethyl ester. The utility of the procedure, which combines the advantage of enzyme immobilization and enzymology in reverse micelles, is illustrated by an example of peptide synthesis. In particular, peptide synthesis (e. g., Z--Ala--Phe--Leu--NH(2)) using water-insoluble substrate has been performed with gelentrapped alpha-chymotrypsin in reverse micellar suspension with the advantage of efficient enzyme recycling.     

Immobilization of cellulolytic and hemicellulolytic enzymes on inorganic supports

Commercial cellulase preparations from Trichoderma viride and Aspergillus niger were immobilized on porous silica glass and ceramics such as alumina and titania with titanium tetrachloride (TiCl(4)) and on their silanized derivatives with glutaraldehyde (GLUT). The amounts of the immobilized enzymes were in the range 10-50 mg/g carrier (dry) depending on the kind of carrier and immobilization method. Their activities toward carboxymethyl cellulose (CMC), xylan, aryl-beta-glucoside, and aryl-beta-xyloside were 3-53% of those of the native enzymes. The optimum pH of the enzymes shifted to the acidic side in most cases, whereas the optimum temperatures were nearly the same as those of native ones. The activity of immobilized enzyme preparations towards CMC did not change significantly during continuous operation over a periods of 60 days. Finally, xylan was hydrolyzed with the immobilized enzymes, and the sugars formed were investigated.     

Protease immobilization onto polyacrolein microspheres

Water-insoluble proteases were prepared by immobilizing papain and chymotrypsin onto the surface of polyacrolein microspheres with and without oligoglycines as spacer. The activity of immobilized proteases was found to be still high toward small ester substrates, but very low toward casein, a high-molecular-weight substrate. The relative activity of the immobilized proteases without spacer decreased gradually with the decreasing surface concentration of the immobilized proteases on the microspheres. On the contrary, the immobilized proteases with oligoglycine spacers gave an almost constant activity for the substrate hydrolysis within the surface concentration region studied and gave a much higher relative activity than those without any spacer. With the longer spacer, the immobilized enzymes showed a higher activity toward casein hydrolysis, whereas there was an optimum length for the spacer when hydrolysis was carried out toward the low-molecular-weight substrate. The thermal stability of the immobilized proteases was higher than that of the respective native proteases. The initial enzymatic activity of the immobilized proteases maintained almost unchanged without any elimination and inactivation of proteases, when the batch enzyme reaction was performed repeatedly, indicating the excellent durability.     

Covalent immobilization of enzymes within micro-aqueous organic media

Traditional covalent immobilization of enzymes was mostly operated within water phase. However, most of enzymes are flexible when they are in water environment, and the covalent reactions generally lead to complete or partial activity losing due to the protein conformational changes.This paper examined enzyme covalent immobilization operated in micro-aqueous organic media, to display the differences between two environments of immobilization within water and micro-aqueous organic solvent by activity and stability determination of the resulting immobilized enzymes. Catalase, trypsin, horseradish peroxidase, laccase and glucose oxidase have been employed as model enzymes. Results showed the thermal, pH and reusable stabilities of the micro-aqueous organic covalently immobilized enzymes were improved when compared with the immobilized enzymes within water. Micro-aqueous covalent immobilization showed a remarkable advantage in remaining the enzymes catalytic activity for all the five enzymes compared with the traditional water phase immobilization. And the optimum pH values for both immobilization within water and micro-aqueous organic media shifted slightly.     

Lactase and other enzymes bound to chitin with glutaraldehyde

Acid tolerant lactase (I), α-chymotrypsin (II), and acid phosphatase (III) were immobilized on chitin with glutaraldehyde. Pretreatments of the chit in with acid, alkali, ammonia, and pronase were compared with respect to release of titratable amino groups and ability to retain lactase activity. Shrimp chitin appeared to be more sensitive to pretreatment conditions and so effort was concentrated on crab. An acid-alkali pretreatment was selected as most practical and economical, and the properties of enzymes fixed on crab chitin were studied intensively. The pH optima of the fixed enzymes were shifted about one pH unit; the shift for I was toward more acid pH, for II was toward alkaline pH, and for III was toward acid pH. The retained activity of immobilized I was approximately 60% that of the native enzyme. A column in continuous operation with I on chitin-glutaraldehyde gave an apparent activity half-life of 27 days.     

Digestion of protein substrates by subtilisin: immobilization changes the pattern of products

Subtilisin BPN' (Bacillus protease strain N') was immobilized on glass-bead carriers of controlled pore size by the glutaraldehyde method. The Vmax and Km values of the synthetic substrate were similar for immobilized and free enzymes. However, the hydrolytic patterns of immobilized and free enzymes toward casein and carboxymethylated lysozyme were different. The free enzyme rapidly hydrolyzed the substrate in the early stage of the reaction to produce peptides of various sizes. The immobilized enzyme, however, slowly digested the casein and lysozyme during digestion; even in the late stage of digestion the original substrates were present in the reaction mixture. The peptide size produced by immobilized enzyme depended on the pore size of the carrier; enzyme immobilized on glass of smaller pore size produced smaller peptide products. These phenomena found with our system of immobilized protease and a protein substrate can be explained by a multiple attack mechanism, in which the substrate that has been forced to enter the matrix is attacked many times by the protease to be completely hydrolyzed, because the substrate and the intermediate-sized product are trapped inside the matrix under reduced diffusion movement. To explain the effective digestion that forms amino acids, we have proposed that a multiple type of attack is responsible for the intracellular protein degradation that takes place in cellular organelles in which hydrolytic enzymes are entrapped.     

Immobilization of lipases for non-aqueous synthesis

Immobilization of lipases involves many levels of complications relating to the structure of the active site and its interactions with the immobilization support. Interaction of the so called hydrophobic ‘lid’ with the support has been reported to affect synthetic activity of an immobilized lipase. In this work we evaluate and compare the synthetic activity of lipases from different sources immobilized on different kinds of supports with varying hydrophobicity. Humicola lanuginosa lipase, Candida antarctica lipase B and Rhizomucor miehei lipase were physically adsorbed onto two types of hydrophobic carriers, namely hydrophilic carriers with conjugated hydrophobic ligands, and supports with base matrix hydrophobicity. The prepared immobilized enzymes were used for acylation of n-butanol with oleic acid as acyl donor in iso-octane with variable water content (0–2.8%, v/v) as reaction medium. Enzyme activity and effect of water on the activity of the immobilized derivatives were compared with those of respective soluble lipases and a commercial immobilized lipase Novozyme 435. Both R. miehei and H. lanuginosa immobilized lipases showed maximum activity at 1.39% (v/v) added water concentration. Sepabeads, a methacrylate based hydrophilic support with conjugated octadecyl chain showed highest immobilized esterification (synthetic) activity for all three enzymes, and of the three R. miehei lipase displayed maximum esterification activity comparable to the commercial enzyme.     

Immobilization of hydrogenases for biophotolytic hydrogen production; stability and kinetics

Summary Hydrogenases from Clostridium pasteurianum and Desulfovibrio desulfuricans were immobilized on solid supports with retention of 50% activity. The immobilized enzymes were more stable than the free enzymes and were active in the biophotolytic hydrogen production from water.     

Characterization and immobilization of E. coli (ATCC-26) Beta-galactosidase

The β-galactosidase from Escherichia coli ATTCC-26 was partially purified and characterized. It was found to be comparable to galactosidases from other E. coli strains in stability, pH and temperature maxima, and activity requirements, but it had a more favorable ratio of activity toward lactose versus synthetic substrates. The galactosidase was immobilized on porous glass beads by three covalent bonding methods. Kinetic data for the free and bound enzymes were determined using natural and synthetic substrates. Activity characteristics of the free and immobilized enzymes were comparable, however, the bound forms were less stable to heat.     

Covalent binding of enzymes to synthetic membranes containing acrylamide units, using formaldehyde

Synthetic membranes containing 10% acrylamide units were subjected to activation with formaldehyde at pH 7.5 and 45 degrees C. Trypsin, invertase, and urease were bound to this activated membrane and the kinetic properties of immobilized enzymes were studied. The permeability of the membrane for distilled water manifests certain differences depending on the enzyme bound. The membranes with immobilized enzymes stored at 4 degrees C in a moist state showed no change in their activity for 6 months. The membrane with immobilized invertase has preserved its activity even after 20 operations with 2% sucrose solution at 25 degrees C. The proposed method of binding enzymes to synthetic membranes containing acrylamide groups, through the introduction of N-hydroxymethyl groups, possesses several advantages with respect to the activation of the membrane in a one-step reaction with cheap and accessible reagent, high operative stability of the immobilized enzymes, no danger of bacterial rotting, and long shelf life of the membrane.     

Immobilization of proteases to porous chitosan beads and their catalysis for ester and peptide synthesis in organic solvents.

alpha-Chymotrypsin (CT), subtilisin BPN' (STB), and subtilisin Carlsberg (STC) were immobilized by adsorption to porous chitosan beads (Chitopearl, CP). The immobilized enzymes showed higher catalytic activities than free enzymes for amino acid esterification in many hydrophilic organic solvents except for methanol and DMF. In ethanol, the initial rate of the esterification increased with water content, whereas in ethyl acetate, the maximum rate was obtained at 2%-3% water. CP-immobilized CT also catalysed transesterification of Ac-Tyr-OMe in ethanol and peptide synthesis in acetonitrile from Ac-Tyr-OH or its ethyl ester and amino acid amides. The immobilized enzymes are highly stable in organic solutions, and can easily be separated from the reaction solutions. Repeated esterifications of Ac-Tyr-OH in acetonitrile by a CP-immobilized CT gave almost constant yields of the ester for more than 3 weeks.     

Polymethylglutamate as a new matrix for covalently immobilized enzymes: Preparation and properties of urease and uricase

Polymethylglutamate (PMG), a synthetic polypeptide, was used as a new carrier to immobilize urease (EC 3.5.1.5) and uricase (EC 1.7.3.3) by the azide method. The enzymes could be immobilized onto PMG in various forms, such as film, fiber, coating on various beads, and a silicon tube. The retained activities of the immobilized enzymes were excellent (more than 95%), therefore it was possible to immobilized almost all activities of the enzymes added in the coupling mixtures. Heat stabilities of the resulting immobilized enzymes were markedly improved, while the optimal pH and K_m values remained almost unchanged. The urease immobilized on the PMG-coated glass beads packed in a column, was found to retain its activity more than 80% of the initial value, even after the occasional use for a year. In view of the improved retained activities and stabilities of the immobilized enzymes, PMG may therefore be a very versatile matrix for the immobilized enzymes.     

小分子封闭提高固定化嗜热菌蛋白酶的热稳定性

为了提高固定化嗜热菌蛋白酶的热稳定性,在制备共价固定化嗜热菌蛋白酶的基础上,通过选择氨基酸和醇类小分子来封闭载体表面未反应的活化基团,并考察了固定化酶的催化活性及热稳定性。结果发现：L-Trp和L-Val封闭修饰固定化酶时,在80℃的水浴中加热150 min后其剩余活力仍为93.4%和98.6%,其效果约为未经小分子封闭的固定化嗜热菌蛋白酶的2倍。所筛选的几种小分子物质中,叔戊醇、L-Trp、L-Val及L-Ala不仅能提高固定化嗜热菌蛋白酶的热稳定性,而且也可以提高固定化酶的相对活力,从而更有利于其在工业生产中的应用。     

Characteristics of nearly dry enzymes in organic solvents: implications for biocatalysis in the absence of water

We have examined enzymes in nearly anhydrous organic solvents spanning a wide range of dielectric constants using a combination of electron paramagnetic resonance (EPR) spectroscopy, molecular dynamics simulations, high-pressure kinetic studies and the electrostatic model of Kirkwood. This approach enabled us to investigate the relationship between catalytic activity, protein flexibility and solvent polarity for an enzymatic reaction proceeding through a highly polar transition state in the near absence of water. Further insights into water-protein interactions and the involvement of water in enzyme structure and function have been obtained by EPR and multinuclear nuclear magnetic resonance studies of enzymes suspended and immobilized in organic solvents with and without added water. In these systems, correlations were observed between the water content and enzyme activity, flexibility, and active-site polarity, although the structural properties of suspended and immobilized enzymes differed markedly. These results have helped to elucidate the role of water in molecular events at the enzymic active site leading to improved biocatalysis in low-water environments.     

Glutathione transferases immobilized on nanoporous alumina: Flow system kinetics,screening, and stability

The previously uncharacterized Drosophila melanogaster Epsilon-class glutathione transferases E6 and E7 were immobilized on nanoporous alumina. The nanoporous anodized alumina membranes were derivatized with 3-aminopropyl-triethoxysilane, and the amino groups were activated with carbonyldiimidazole to allow coupling of the enzymes via ε-amino groups. Kinetic analyses of the immobilized enzymes were carried out in a circulating flow system using CDNB (1-chloro-2,4-dinitrobenzene) as substrate, followed by specificity screening with alternative substrates. A good correlation was observed between the substrate screening data for immobilized enzyme and corresponding data for the enzyme in solution. A limited kinetic study was also carried out on immobilized human GST S1-1 (also known as hematopoietic prostaglandin D synthase). The stability of the immobilized enzymes was virtually identical to that of enzymes in solution, and no leakage of enzyme from the matrix could be observed.     

Characterization of sand as a support for immobilized enzymes.

The potential of sand as a support for immobilized enzymes was investigated by preparing alkylamine sand and devising methods to measure the total number of amine groups present and the fraction available for immobilization of enzymes. Alcohol dehydrogenase (alcohol: NAD oxidoreductase, EC 1.1.1.1.) and lactate dehydrogenase (L-lactate:NAD oxidoreductase, EC 1.1.1.27) were immobilized on alkylamine sand, and the stability of the immobilized protein and dehydrogenase activity was measured. Urease (urea amidohydrolase, EC 3.5.1.5) was also immobilized on sand to test the applicability of these methods to larger scale immobilizations. Results suggest that sand shows promise as a support for immobilized enzymes.     

Immobilization and stabilization of α-galactosidase on Sepabeads EC-EA and EC-HA

α-Galactosidase from tomato has been immobilized on Sepabead EC-EA and Sepabead EC-HA, which were activated with ethylendiamino and hexamethylenediamino groups, respectively. Two strategy was used for the covalent immobilization of α-galactosidase on the aminated Sepabeads: covalent immobilization of enzyme on glutaraldehyde activated support and cross-linking of the adsorbed enzymes on to the support with glutaraldehyde. By using these two methods, all the immobilized enzymes retained very high activity and the stability of the enzyme was also improved. The obtained results showed that, the most stable immobilized α-galactosidase was obtained with the second strategy. The immobilized enzymes were characterized with respect to free counterpart. Some parameters effecting to the enzyme activity and stability were also analyzed. The optimum temperature and pH were found as 60 °C and pH 5.5 for all immobilized enzymes, respectively. All the immobilized α-galactosidases were more thermostable than the free enzyme at 50 °C. The stabilities of the Sepabead EC-EA and EC-HA adsorbed enzymes treated with glutaraldehyde compared to the stability of the free enzyme were a factor of 6 for Sepabead EC-EA and 5.3 for Sepabead EC-HA. Both the free and immobilized enzymes were very stable between pH 3.0 and 6.0 and more than 85% of the initial activities were recovered. Under the identical storage conditions the free enzyme lost its initial activity more quickly than the immobilized enzymes at the same period of time. The immobilized α-galactosidase seems to fulfill the requirements for different industrial applications.     

Lipoprotein lipase immobilization onto polyacrolein microspheres

A lipoprotein lipase (LPL) was made water insoluble by immobilizing onto the surface of polyacrolein (PAA) microspheres with and without oligoglycines as spacer. The activity of the immobilized LPL was found to remain high toward a small ester substrate, p-nitrophenyl laurate (pNPL). The relative activity of the immobilized LPL without spacer decreased gradually with the decreasing surface concentration of the immobilized LPL on the PAA microsphere. On the contrary, the immobilized LPL with oligoglycine spacers gave an almost constant activity for the substrate hydrolysis within the surface concentration region studied and gave a much higher relative activity than that without any spacer. The Michaelis constant K(m) and the maximum reaction velocity V(m) were estimated for the free and the immobilized LPL. The apparent K(m) was larger for the immobilized LPL than for the free one, while V(m) was smaller for the immobilized LPL. The pH, thermal, and storage stabilities of the immobilized LPL were higher than those of the free one. The initial enzymatic activity of the immobilized LPL maintained almost unchanged without any leakage and inactivation of LPL when the batch enzyme reaction was performed repeatedly, indicating the excellent durability of the immobilized LPL.     

Preparation and application of poly(N,N-dimethylacrylamide-co-acrylamide) and poly(N-isopropylacrylamide-co-acrylamide)/kappa-Carrageenan hydrogels for immobilization of lipase

In the present of this study, two novel polymeric matrixes that are poly(N,N-dimethylacrylamide-co-acrylamide) and poly(N-isopropylacrylamide-co-acrylamide)/kappa-Carrageenan was synthesized and applied for immobilization of lipase. For the immobilization of enzyme, two different immobilization procedures have been carried out via covalently binding and entrapment methods. On the free and immobilized enzymes activities, optimum pH, temperature, storage and thermal stability was investigated. The optimum temperature for free, covalently immobilized and entrapped enzymes was found to be 30, 35 and 30 degrees C, respectively. Optimum pH for both free and immobilized enzymes was also observed at pH 8. Maximum reaction rate (Vmax) and Michaelis-Menten constant (Km) were determined for free and immobilized lipases. Furthermore, the reuse numbers of immobilized enzymes also studied. It was observed that after 40th use in 5 days, the retained activities for covalently immobilized and entrapped lipases were found as 39% and 22%, respectively. Storage and thermal stability of enzyme was also increased by as a result of immobilization procedures.     

Characterization of CIM monoliths as enzyme reactors

The immobilization of the enzymes citrate lyase, malate dehydrogenase, isocitrate dehydrogenase and lactate dehydrogenase to CIM monolithic supports was performed. The long-term stability, reproducibility, and linear response range of the immobilized enzyme reactors were investigated along with the determination of the kinetic behavior of the enzymes immobilized on the CIM monoliths. The Michaelis-Menten constant K(m) and the turnover number k(3) of the immobilized enzymes were found to be flow-unaffected. Furthermore, the K(m) values of the soluble and immobilized enzyme were found to be comparable. Both facts indicate the absence of a diffusional limitation in immobilized CIM enzyme reactors.