Enzymatic interesterification of triglyceride with surfactant-coated lipase in organic media

Comparison between Lipase Performance Distributed at the O/W Interface by Membrane Emulsification and by Mechanical Stirring

Multiphase bioreactors using interfacial biocatalysts are unique tools in life sciences such as pharmaceutical and biotechnology. In such systems, the formation of microdroplets promotes the mass transfer of reagents between two different phases, and the reaction occurs at the liquid-liquid interface. Membrane emulsification is a technique with unique properties in terms of precise manufacturing of emulsion droplets in mild operative conditions suitable to preserve the stability of bioactive labile components. In the present work, membrane emulsification technology was used for the production of a microstructured emulsion bioreactor using lipase as a catalyst and as a surfactant at the same time. An emulsion bioreaction system was also prepared by the stirring method. The kinetic resolution of (S,R)-naproxen methyl ester catalyzed by the lipase from Candida rugosa to obtain (S)-naproxen acid was used as a model reaction. The catalytic performance of the enzyme in the emulsion systems formulated with the two methods was evaluated in a stirred tank reactor and compared. Lipase showed maximum enantioselectivity (100%) and conversion in the hydrolysis of (S)-naproxen methyl ester when the membrane emulsification technique was used for biocatalytic microdroplets production. Moreover, the controlled formulation of uniform and stable droplets permitted the evaluation of lipase amount distributed at the interface and therefore the evaluation of enzyme specific activity as well as the estimation of the hydrodynamic radius of the enzyme at the oil/water (o/w) interface in its maximum enantioselectivity.

Lignin for Nano- and Microscaled Carrier Systems: Applications, Trends, and Challenges

To liberate society from its dependence on fossil-based fuels and materials it is pivotal to explore components of renewable plant biomass in applications that benefit from their intrinsic biodegradability, safety, and sustainability. Lignin, a byproduct of the pulp and paper industry, is a plausible material for carrying various types of cargo in small- and large-scale applications. Herein, possibilities and constraints regarding the physical-chemical properties of the lignin source as well as modifications and processing required to render lignins suitable for the loading and release of pesticides, pharmaceuticals, and biological macromolecules is reviewed. In addition, the technical challenges, regulatory and toxicological aspects, and future research needed to realize some of the promises that nano- and microscaled lignin materials hold for a sustainable future are critically discussed.

Spatially confined lignin nanospheres for biocatalytic ester synthesis in aqueous media

Dehydration reactions proceed readily in water-filled biological cells. Development of biocatalysts that mimic such compartmentalized reactions has been cumbersome due to the lack of low-cost nanomaterials and associated technologies. Here we show that cationic lignin nanospheres function as activating anchors for hydrolases, and enable aqueous ester synthesis by forming spatially confined biocatalysts upon self-assembly and drying-driven aggregation in calcium alginate hydrogel. Spatially confined microbial cutinase and lipase retain 97% and 70% of their respective synthetic activities when the volume ratio of water to hexane increases from 1:1 to 9:1 in the reaction medium. The activity retention of industrially most frequently used acrylic resin-immobilized Candida antarctica lipase B is only 51% under similar test conditions. Overall, our findings enable fabrication of robust renewable biocatalysts for aqueous ester synthesis, and provide insight into the compartmentalization of diverse heterogeneous catalysts.

Spatially confined lignin nanospheres for biocatalytic ester synthesis in aqueous media

Dehydration reactions proceed readily in water-filled biological cells. Development of biocatalysts that mimic such compartmentalized reactions has been cumbersome due to the lack of low-cost nanomaterials and associated technologies. Here we show that cationic lignin nanospheres function as activating anchors for hydrolases, and enable aqueous ester synthesis by forming spatially confined biocatalysts upon self-assembly and drying-driven aggregation in calcium alginate hydrogel. Spatially confined microbial cutinase and lipase retain 97% and 70% of their respective synthetic activities when the volume ratio of water to hexane increases from 1:1 to 9:1 in the reaction medium. The activity retention of industrially most frequently used acrylic resin-immobilized Candida antarctica lipase B is only 51% under similar test conditions. Overall, our findings enable fabrication of robust renewable biocatalysts for aqueous ester synthesis, and provide insight into the compartmentalization of diverse heterogeneous catalysts.

Development of biocatalysts that mimic compartmentalized reactions in cells has been cumbersome due to the lack of low-cost materials and associated technologies. Here the authors show that cationic lignin nanospheres function as activating anchors for hydrolases, and enable aqueous ester synthesis by forming spatially confined biocatalysts.

Effect of Additives on the Selectivity and Reactivity of Enzymes

Enzymes have been widely used as efficient, eco-friendly, and biodegradable catalysts in organic chemistry due to their mild reaction conditions and high selectivity and efficiency. In recent years, the catalytic promiscuity of many enzymes in unnatural reactions has been revealed and studied by chemists and biochemists, which has expanded the application potential of enzymes. To enhance the selectivity and activity of enzymes in their natural or promiscuous reactions, many methods have been recommended, such as protein engineering, process engineering, and media engineering. Among them, the additive approach is very attractive because of its simplicity to use and high efficiency. In this paper, we will review the recent developments about the applications of additives to improve the catalytic performances of enzymes in their natural and promiscuous reactions. These additives include water, organic bases, water mimics, cosolvents, crown ethers, salts, surfactants, and some particular molecular additives.

Solid-in-oil dispersion: a novel core technology for drug delivery systems

Drug delivery systems using a solid-in-oil (S/O) dispersion as a core technology have advanced significantly over the past ten years. A novel, effective and practical preparation method for a S/O dispersion was originally established in 1997 as a tool for enzymatic catalysis in organic media. This oil-based dispersion containing proteins in non-aqueous media had great potential for applications to other research with one of the most successful being its adaptation as a drug delivery system. The history and features of novel processes for preparing S/O dispersions are presented in this article. In addition, recent research into the use of S/O dispersions for innovative oral and skin drug delivery systems is discussed.

Surfactant-modified yeast whole-cell biocatalyst displaying lipase on cell surface for enzymatic production of structured lipids in organic media

The cell surface engineering system, in which functional proteins are genetically displayed on microbial cell surfaces, has recently become a powerful tool for applied biotechnology. Here, we report on the surfactant modification of surface-displayed lipase to improve its performance for enzymatic synthesis reactions. The lipase activities of the surfactant-modified yeast displaying Rhizopus oryzae lipase (ROL) were evaluated in both aqueous and nonaqueous systems. Despite the similar lipase activities of control and surfactant-modified cells in aqueous media, the treatment with nonionic surfactants increased the specific lipase activity of the ROL-displaying yeast in n-hexane. In particular, the Tween 20-modified cells increased the cell surface hydrophobicity significantly among a series of Tween surfactants tested, resulting in 8-30 times higher specific activity in organic solvents with relatively high log P values. The developed cells were successfully used for the enzymatic synthesis of phospholipids and fatty acid methyl esters in n-hexane, whereas the nontreated cells produced a significantly low yield. Our results thus indicate that surfactant modification of the cell surface can enhance the potential of the surface-displayed lipase for bioconversion.

Increased Enantioselectivity and Remarkable Acceleration of Lipase-Catalyzed Transesterification by Using an Imidazolium PEG–Alkyl Sulfate Ionic Liquid

Several types of imidazolium salt ionic liquids were prepared derived from poly(oxyethylene)alkyl sulfate and used as an additive or coating material for lipase-catalyzed transesterification in an organic solvent. A remarkably increased enantioselectivity was obtained when the salt was added at 3-10 mol % versus substrate in the Burkholderia cepacia lipase (lipase PS-C)-catalyzed transesterification of 1-phenylethanol by using vinyl acetate in diisopropyl ether or a hexane solvent system. In particular, a remarkable acceleration was accomplished by the ionic liquid coating with lipase PS in an iPr(2)O solvent system while maintaining excellent enantioselectivity; it reached approximately 500- to 1000-fold acceleration for some substrates with excellent enantioselectivity. A similar acceleration was also observed for IL 1-coated Candida rugosa lipase. MALDI-TOF mass spectrometry experiments of the ionic-liquid-coated lipase PS suggest that ionic liquid binds with lipase protein.

Production of ascorbyl palmitate by surfactant-coated lipase in organic media

The surface of a lipase from Burkholderia cepacia was coated with a nonionic surfactant, propylene glycol monostearate, and was used as a biocatalyst in the production of ascorbic acid in tert-butyl alcohol. The influence of various factors such as the type of surfactant, the pH of the buffer used for coating, the amount of surfactant in the coating, the organic solvent, and the temperature and molar ratio of the substrates used in the reaction on the conversion of ascorbyl palmitate were studied. After 24 h of reaction at 50 degrees C, a conversion of 47% was obtained using an ascorbic acid to palmitic acid molar ratio of 1:6. The native lipase showed only 6% conversion.

Why do crown ethers activate enzymes in organic solvents?

One of the major drawbacks of enzymes in nonaqueous solvents is that their activity is often dramatically low compared to that in water. This limitation can be largely overcome by crown ether treatment of enzymes. In this paper, we describe a number of carefully designed new experiments that have improved the insights into the mechanisms that are operative in the crown ether activation of enzymes in organic solvents. The enhancement of enzyme activity upon addition of 18-crown-6 to the organic solvent can be reconciled with a mechanism in which macrocyclic interactions of 18-crown-6 with the enzyme play an important role. Macrocyclic interactions (e.g., complexation with lysine ammonium groups of the enzyme) can lead to a reduced formation of inter- and intramolecular salt bridges and, consequently, to lowering of the kinetic conformational barriers, enabling the enzyme to refold into thermodynamically stable, catalytically (more) active conformations. This assumption is supported by the observation that the crown-ether-enhanced enzyme activity is retained after removal of the crown by washing with a dry organic solvent. A much stronger crown ether activation is observed when 18-crown-6 is added prior to lyophilization, and this can be explained by a combination of two effects: the before-mentioned macrocyclic complexation effect, and a less specific, nonmacrocyclic, lyoprotecting effect. The magnitude of the total crown ether effect depends on the polarity and thermodynamic water activity of the solvent, the activation being highest in dry and apolar media, where kinetic conformational barriers are highest. By determination of the specific activity of crown-ether-lyophilized enzyme as a function of the enzyme concentration, the macrocyclic crown ether (linearly dependent on the enzyme concentration) and the nonmacrocyclic lyoprotection effect (not dependent on the enzyme concentration) could be separated. These measurements reveal that the contribution of the nonmacrocyclic effect is significantly larger than the macrocyclic refolding effect.

A study on the surface hydrophobicity of lipases

Surface properties, including surface net and local hydrophobicities, of bovine serum albumin, gamma-globulin, and six lipases of different origins were evaluated using the aqueous two-phase partitioning method. Each showed a specific and characteristic pattern of surface properties. Correlations between the protein surface hydrophobicities and the coverages of the proteins by lipid-coating with a synthetic detergent, dioleyl glucosyl L-glutamate, were discussed. The results indicated that the surface net hydrophobicity of each protein was indicative of the affinity of the protein for the coating detergent applied in lipid-coating.

Enantioselective recognition mechanism of secondary alcohol by surfactant-coated lipases in nonaqueous media

The enantioselective recognition mechanism of secondary alcohol by lipases originated from Candida rugosa and Pseudomonas cepacia was elucidated on the basis of the kinetic study of the esterification of alcohol with lauric acid in isooctane. To obtain inherent kinetic parameters, we utilized a surfactant-coated lipase whose conformation is considered to be an "open" form in a homogeneous organic solvent. Based on the experimental results, the enantioselectivity of lipases was found to be derived from the difference in the V(max) values between the two enantiomers. The same result was observed when lipases of different origin and substrates with different molecular structures were applied. &copy 1999 John Wiley & Sons, Inc.

Trapping of different lipase conformers in water-restricted environments

Based on a recently reported strategy to rationally activate lipolytic enzymes for use in nonaqueous media [Mingarro, I., et al. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 3308-3312], we compared the behavior in water-restricted environments of activated vs nonactivated forms of different lipases toward their natural substrates, triacylglycerols. To this end, nine lipases from varied origins (mammalian, fungal, and bacterial) were assayed using simple acidolyses as nonaqueous model reactions. The experimental results for several (though not all) lipases, discussed in the light of current structural and functional information, were collectively consistent with a model where, depending on the "history" of sample preparation, basically two different conformers (open and closed) of the lipase can be trapped (and assayed) in the nonaqueous medium. In particular, for a few prototypic lipases investigated in more detail, the following were shown: (i) the activation strategy permitted them to rationally overcome their reported reluctance to convert saturated, long-chain triglycerides, providing quantifiable nonaqueous rate accelerations of up to 3 orders of magnitude; (ii) the activated conformer exhibited a markedly higher ability than its nonactivated counterpart to bind a ligand (nonhydrolyzable phospholipid) in the nonaqueous medium; and (iii) a clearly distinct selectivity profile toward the substrate chain length was obtained for either conformer.