Extraction of enzymes by reverse micelles

Protein crystal occurrence domains in selective protein crystallisation for bio-separation

Bio-separation is a key bottleneck in the manufacture of biopharmaceuticals.

Influence of different parameters on reverse micelle extraction combined with acetone precipitation to purify sn-1,3 extracellular lipase from Aspergillus niger GZUF36

There are few reports on the feasibility of combined reverse micelle extraction and acetone precipitation to obtain electrophoretic pure enzymes. We aimed to purify a sn-1,3 extracellular lipase from a novel Aspergillus niger GZUF36 through this combination in this work. This lipase preliminarily purified by controlling the volume ratio (1:2.5) of crude enzyme solution and acetone. Then, we studied effects of different parameters on reverse micelle extraction. The suitable surfactant, pH, salt and cosolvent and extraction time for forward extraction were 125 mM cetyl trimethylammonium bromide (CTAB), 9.0, 0.075 M NaCl, 10% n-hexanol and 30 min, respectively. Under these conditions, the forward extraction rate reached 90.3% ± 3.2%. The suitable salt, pH, extraction time and short chain alcohol for backward extraction were consecutively 1.5 M KCl, 6.5, 60 min and 10% ethanol. Adding 10% ethanol shows a significant advantage of improvement the extraction rate. Under these optimal conditions, the total extraction rate and purification factor of lipase reached 76.8% and 10.14, respectively. SDS-PAGE showed that molecular weight of the pure protein was 42.7 kDa and TLC exhibited sn-1,3 selectivity of this lipase. LC-MS/MS analysis revealed that the lipase had 297 amino acid residues and was likely to glycosylate. Through the study of different parameters, it demonstrated that the new and simple combination of reverse micelle extraction using CTAB as surfactant and n-hexanol as cosolvent for forward extraction and adding ethanol for backward extraction and acetone precipitation is a promising method to get almost an electrophoretically pure sn-1,3 lipase.

Selective extraction of lactoferrin from acidic whey using CTAB/n-heptanol reverse micellar system

A reverse micellar system comprising CTAB/n-heptanol, developed for extracting lactoferrin (LF) from a synthetic solution of LF, was investigated for the selective extraction of LF from synthetic whey protein solution, which was prepared by mixing the pure whey proteins. The process conditions obtained during the process was further extended to extract the LF from real acidic whey. The selective extraction of LF was improved by studying the effect of NaCl concentration (additive) and aqueous phase pH on the partitioning of LF into the micellar phase. The highest extraction of LF (98.7%) from acidic whey to micellar phase was achieved at the aqueous phase pH of 10.3 and NaCl concentration of 1.1 M. The LF was back extracted to the aqueous stripping phase with 94% extraction efficiency and 100% purity. The recycling capacity of the organic phase after the back extraction of LF was analyzed to make the process more economical.

Selective extraction of lipase and amylase from enzyme mixture by employing liquid emulsion membrane

This work deals with the extraction of lipase and amylase from enzyme mixture by employing liquid emulsion membranes (LEM). The electrostatic interaction between enzymes and reverse micellar surfactant polar head group plays an important role for selective extraction of two different enzymes having different isoelectric points. The optimized conditions for lipase extraction (pH 7.0) resulted in the purification fold and activity recovery of 5.43 fold and 89.53%, respectively, whereas, in case of amylase (pH 9.0) the purification fold and activity recovery were 6.58 and 94.32%, respectively. The results were compared with the control sample (containing individual enzymes) and mixture of enzymes lipase and amylase and it was shown that for optimum conditions the activity recovery and purification fold was higher for the individual enzymes as compared to their mixture. Downstream processing involving LEM was shown to be a feasible method for selective extraction of enzymes. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:721-729, 2018.

Reverse micellar extraction of lactoferrin from its synthetic solution using CTAB/n-heptanol system

The partitioning of Lactoferrin (LF) into the reverse micellar phase formed by a cationic surfactant, cetyltrimethylammonium bromide (CTAB) in n-heptanol from the synthetic solution of LF was studied. The solubilization behaviour of LF into the reverse micellar phase and back extraction using a fresh stripping phase were improved by studying the effect of processing parameters, including surfactant concentration, solution pH, electrolyte salt concentration and addition of alcohol as co-solvent. Forward extraction of 100% was achieved at CTAB concentration of 50 mM in n-heptanol solvent, pH of 10 and 1 M NaCl. The electrostatic force and hydrophobic interaction have major influence on LF extraction during forward and back extraction respectively. The size of the reverse micelles and their corresponding water content were measured at different operating conditions to assess their role on the LF extraction. The present reverse micellar system has potential to solubilise almost all the LF into the reverse micelles during forward extraction and could able to allow back extraction from the reverse micellar phase with addition of small amount of co-solvent.

New phases found in reverse micelle systems with high concentrations of AOT

This paper discusses the phase behavior, rheology, and structure of self-assembled sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelle systems at high AOT concentrations. When the amount of AOT and w(o) (the molar ratio of water to AOT) were changed, many different phases were found, a fact which is not discussed in the literature. Opaque gel-like phase (phase separation) occurred with high concentrations of AOT in organic solvents without water. When the AOT concentration and w(o) were increased to 18-72 m and 2, respectively, the samples were gel-like and translucent. Dynamic rheological results indicate that the viscoelastic transition agreed with a multirelaxation time model. Small-angle X-ray scattering (SAXS) results imply that these samples showed a hexagonally close-packed cylindrical structure in which the diameter of a cylinder was ~2.5-3.0 nm, depending on the water contents. Moreover, these AOT cylinders self-assembled into fiber bundles with a diameter of 1-10 μm, as determined using a polarized optical microscope. As w(o) was increased to 2-6 in 72 m AOT samples, similar rheological and SAXS results were obtained. However, a different type of viscoelastic transition occurred, from multirelaxation to single-relaxation, when w(o) was increased to 7-11. The samples were in the transparent gel-like phase, and the structures determined by SAXS were a combination of hexagonally packed cylindrical and lamellar structure. The close-packed cylindrical structures had larger radii and shorter lengths with increasing w(o). Furthermore, when w(o) was increased to 12, the gel-like phase disappeared and a highly viscous solution was observed. This is because all the cylindrical structures collapsed and transformed into lamellar structures when the amount of water was further increased.

Extraction of monoclonal antibodies (IgG1) using anionic and anionic/nonionic reverse micelles

Purification schemes for antibody production based on affinity chromatography are trying to keep pace with increases in cell culture expression levels and many current research initiatives are focused on finding alternatives to chromatography for the purification of Monoclonal antibodies (MAbs). In this article, we have investigated an alternative separation technique based on liquid-liquid extraction called the reverse micellar extraction. We extracted MAb (IgG1) using reverse micelles of an anionic surfactant, sodium bis 2-ethyl-hexyl sulfosuccinate (AOT) and a combination of anionic (AOT) and nonionic surfactants (Brij-30, Tween-85, Span-85) using isooctane as the solvent system. The extraction efficiency of IgG1 was studied by varying parameters, such as pH of the aqueous phase, cation concentration, and type and surfactant concentration. Using the AOT/Isooctane reverse micellar system, we could achieve good overall extraction of IgG1 (between 80 and 90%), but only 30% of the bioactivity of IgG1 could be recovered at the end of the extraction by using its binding to affinity chromatography columns as a surrogate measure of activity. As anionic surfactants were suspected as being one of the reasons for the reduced activity, we decided to combine a nonionic surfactant with an anionic surfactant and then study its effect on the extraction efficiency and bioactivity. The best results were obtained using an AOT/Brij-30/Isooctane reverse micellar system, which gave an overall extraction above 90 and 59% overall activity recovery. An AOT/Tween-85/Isooctane reverse micellar system gave an overall extraction of between 75 and 80% and overall activity recovery of around 40-45%. The results showed that the activity recovery of IgG1 can be significantly enhanced using different surfactant combination systems, and if the recovery of IgG1 can be further enhanced, the technique shows considerable promise for the downstream purification of MAbs.

A metal-chelate affinity reverse micellar system for protein extraction

A new nonionic reverse micellar system is developed by blending two nonionic surfactants, Triton X-45 and Span 80. At total surfactant concentrations lower than 60 mmol/L and molar fractions of Triton X-45 less than 0.6, thermodynamically stable reverse micelles of water content (W(0)) up to 30 are formed. Di(2-ethylhexyl) phosphoric acid (HDEHP; 1-2 mmol/L) is introduced into the system for chelating transition metal ions that have binding affinity for histidine-rich proteins. HDEHP exists in a dimeric form in organic solvents and a dimer associated with one transition metal ion, including copper, zinc, and nickel. The copper-chelate reverse micelles (Cu-RM) are characterized for their W(0), hydrodynamic radius (R(h)), and aggregation number (N(ag)). Similar with reverse micelles of bis-2-ethylhexyl sodium sulfosuccinate (AOT), R(h) of the Cu-RM is also linearly related to W(0). However, N(ag) is determined to be 30-90 at W(0) of 5-30, only quarter to half of the AOT reverse micelles. Then, selective metal-chelate extraction of histidine-rich protein (myoglobin) by the Cu-RM is successfully performed with pure and mixed protein systems (myoglobin and lysozyme). The solubilized protein can be recovered by stripping with imidazole or ethylinediaminetetraacetic acid (EDTA) solution. Because various transition metal ions can be chelated to the reverse micelles, it is convinced that the system would be useful for application in protein purification as well as simultaneous isolation and refolding of recombinant histidine-tagged proteins expressed as inclusion bodies.

Electrochemical aspects of the reverse micelle extraction of proteins

The mechanism of the solvent extraction of cytochrome c (Cyt c) via reverse micelle formation was studied from an electrochemical point of view. Potentiometric measurements showed that the Galvani potential difference of the oil/water (O/W) interface played a crucial role in the spontaneous extraction of Cyt c with bis(2-ethylhexyl)sulfosuccinate (AOT). However, the dependence of the extraction efficiency on the concentration of an aqueous electrolyte (KCl) could be explained not by the effect of the interfacial potential, but by the change in the interfacial tension (gamma). Electrocapillary measurements showed that the adsorption of AOT anions to the O/W interface resulted in a significant decrease of gamma in a higher potential range, where reverse micelles were formed. The bottom level of gamma in the higher potential range was increased with [KCl]. The lower extraction efficiency for higher [KCl]'s was elucidated by a "size exclusion effect". This was also supported by water-content measurements by the Karl Fisher method.

Purification of Glucose Oxidase from Aspergillus niger by Liquid-Liquid Cationic Reversed Micelles Extraction

The aim of this work was to select the operating conditions for the extraction and recovery of glucose oxidase (GOX) by reversed micelles from mixtures of commercial enzyme and Aspergillus niger homogenates. For this purpose, the influence of the main operating parameters (pH, surfactant concentration, and presence of cell debris or not) on GOX extraction was investigated at 25 degrees C. Without cell debris, the highest yield of GOX activity recovery (90.8%) was obtained performing (a) the forward extraction in isooctane as solvent and hexanol and butanol as cosolvents at 76/6/18 ratio, pH 7.0, 0.2 M cetyl trimethylammonium bromide as cationic surfactant, and electric conductivity of 5.0 mS cm(-1) and (b) the backward extraction at pH 5.5. Forward and backward extractions furnished comparable results when using raw homogenate, which demonstrates a negligible impact of the presence of cell debris on the process. The highest extraction yield (94%) was obtained under the same forward and backward conditions adopted without cell debris. The promising results of this work suggest that the proposed methodology could be profitably exploited at an industrial level.

Effect of hexanol on the reversed micelles of Span 85 modified with Cibacron Blue F-3GA for protein solubilization

Sorbitan trioleate (Span 85) modified with Cibacron Blue F-3GA (CB) was used as an affinity surfactant (CB-Span 85) to form affinity-based reversed micelles in n-hexane. It was found that the addition of hexanol to the reversed micellar system resulted in a significant increase in water content and hydrodynamic radius of the affinity-based reversed micelles. Moreover, the reversed micelles with hexanol revealed broader aggregation number distribution and larger average aggregation number than the reversed micelles without hexanol addition. This is considered to be due to the decreases in the micellar curvature and rigidity of the micellar interfacial layer and the increase in the micellar interfacial fluidity. Consequently, the solubilization capacity of lysozyme increased about 70% in the reversed micellar solution with 3 vol% hexanol. On the other hand, the capacity of BSA was only 30% increased under the same conditions due to its larger molecular size than lysozyme. Kinetic analysis revealed that the increase in the micellar interfacial fluidity in the presence of hexanol resulted in faster release of lysozyme from the micelles, thus leading to an increase of the overall volumetric mass transfer coefficient in the back extraction.

Characterization of reversed micelles of Cibacron Blue F-3GA modified Span 85 for protein solubilization

The nonionic surfactant of sorbitan trioleate (Span 85) was modified with Cibacron Blue F-3GA (CB) as an affinity surfactant (CB-Span 85) to form affinity-based reversed micelles in n-hexane. The reversed micelles formed by the mixture of Span 85 and CB-Span 85 conjugate were extensively characterized in water content, hydrodynamic radius, and aggregation number. The results show that the water content and hydrodynamic radius of the reversed micelles were significantly increased by the introduction of CB ligands (CB-Span 85 conjugate), and the reversed micelles with CB-Span 85 conjugate had a wider aggregation number distribution than the Span 85 reversed micelles. Using lysozyme as a model protein, protein solubilization by the reversed micelles was investigated. Lysozyme solubilization increased significantly with the coupled CB concentration, indicating that the extraction was based upon the affinity interactions between lysozyme molecules and the CB ligand. High solubilization of lysozyme was obtained by the affinity-based reversed micelles of 62.7 mmol/L Span 85 with coupled CB higher than 0.25 mmol/L. Lysozyme recovery was carried out using a stripping solution of high ionic strength. The recovered lysozyme exhibited an activity equivalent to the native lysozyme and its secondary structure was also unchanged. The results indicate that the reversed micellar system would find potential application in protein separation.

Preparation of ZnS/CdS composite nanoparticles by coprecipitation from reverse micelles using CO2 as antisolvent

The possibility of simultaneously recovering ZnS and CdS particles from reverse micelles by dissolving antisolvent CO2 into the micellar solution was investigated by high-pressure UV-Vis spectra. It was found that all the ZnS and CdS particles in the reverse micelles could be precipitated by compressed CO2 at suitable pressures. The phase structures and morphologies of the obtained composites were characterized by X-ray diffraction and transmission electronic micrographs. The results illustrate that the smaller molar ratio of water to surfactant of the reverse micelles and higher pressure of CO2 are favorable for producing smaller particles. This method has many potential advantages for the production of composite nanoparticles.

Selective precipitation and recovery of xylanase using surfactant and organic solvent

The selective precipitation of xylanase from an aqueous phase containing mixtures of xylanase and cellulase was studied using an ionic surfactant as precipitating ligand and a polar organic solvent as recovery solvent. Of four ionic surfactants tested, sodium di-(2-ethylhexyl) sulfosuccinate (AOT) showed a complete removal of xylanase at pH 4.5. The recovery of xylanase from the xylanase-AOT complex was a strong function of the type and the volume of the polar solvent and of the concentration of sodium acetate buffer in the final aqueous solution used to solubilize the recovered xylanase. With ethanol as a recovery solvent, a recovery of xylanase activity of 78 +/- 10% was obtained. The cellulase activity in the recovered xylanase was below the detection limit. The results demonstrate that an ionic surfactant can recover enzymes from aqueous solutions without loss in their activity.

Study of the factors affecting the forward and back extraction of yeast-lipase and its activity by reverse micelles

The experimental results of yeast-lipase extracted by AOT-reverse-micelles in isooctane are reported. The effects of pH values and ionic strength in the aqueous phase, surfactant concentration, phase volume ratio, temperature, stirring time, and cosolvent concentration on the phase transfer of the lipase by the reverse micelles are studied. One hundred percent of forward extraction yield, 68% of back extraction yield, and 45% of activity recovery yield for the lipase are obtained. The phase transfer of the lipase is controlled by electrostatic and hydrophobic interactions.

Extraction of immunoglobulin-G from colostral whey by reverse micelles

Separation of immunoglobulin G (IgG) from the other colostral whey proteins was carried out by reversed micellar extraction. The colostral whey was diluted to 5 times its original volume with 50 mM phosphate buffer at pH 6.35 containing 100 mM of sodium chloride. The aqueous solution was then mixed with an equal volume of isooctane containing 50 mM bis-(2-ethylhexyl) sodium sulfosuccinate (AOT), and shaken at 200 rpm and 25 degrees C for 10 min. After extraction, the mixture was separated to the aqueous phase and the reversed micellar phase by centrifugation. This procedure extracted most of the non-IgG proteins to the reversed micellar phase and recovered more than 90% of the IgG in the aqueous phase. The IgG in the aqueous phase had a purity of 90%, and still possessed immunological activity. AOT was not detectable in the aqueous phase.

Solubilization limit of lysozyme into DODMAC reverse micelles

Dioctyldimethyl ammonium chloride (DODMAC) was used to form reverse micelles and to extract lysozyme from an aqueous solution into an organic phase. The solubilization behavior of lysozyme into a DODMAC reverse micellar phase was examined in terms of the temperature, the type of cations in the aqueous phase, and the surfactant concentration in the organic phase. Complete removal of lysozyme from the aqueous phase was obtained when the pH was set one unit higher than the pI of the protein. However, it was found that there is a solubilization limit of lysozyme in the organic phase. Not all the lysozyme extracted out of the initial aqueous phase was solubilized into the DODMAC reverse micellar phase, resulting in the formation of white precipitate at the aqueous-organic interface. Temperature has a negligible effect on the solubilization limit of lysozyme. The value of the solubilization limit is a strong function of the type of cations present in the aqueous phase, indicating an important role of lysozyme-cation interactions on the extraction process. An increase in the DODMAC concentration from 100-200 mM resulted in little change in the highest concentration of lysozyme obtained in the organic phase.

Reverse micelles and protein biotechnology

Reverse micelles are nanometer-sized (1-10 nm) water droplets dispersed in organic media obtained by the action of surfactants. Surfactant molecules organize with the polar part to the inner side able to solubilize water and the apolar part in contact with the organic solvent. Proteins can be solubilized in the water pool of reverse micelles. Studies on the structure-function relationships of proteins in reverse micelles are very important since the microenvironment in which the protein is solubilized has physico-chemical properties distinct from a bulk aqueous solution. Some of the unique characteristics of reverse micelles make them very useful for biotechnological applications. Charge and hydrophilic/hydrophobic characteristics of the protein and the selection of surfactant can be used to achieve selective solubilization of proteins. This has been used to extend the classical liquid-liquid extraction with solvents to protein bioseparation. For biocatalysis the presence of a bulk organic solvent allow synthetic reactions to be performed via the control of water content and the solubilization of hydrophobic substrates. This is accomplished with a higher interfacial area (about 100 m2/mL) than the conventional biphasic systems, minimizing mass transfer problems.

Reverse micellar extraction for downstream processing of proteins/enzymes

New developments in the area of downstream processing are, hopefully, to fulfill the promises of modern biotechnology. The traditional separation processes such as chromatography or electrophoresis can become prohibitively expensive unless the product is of high value. Hence, there is a need to develop efficient and cost-effective downstream processing methods. Reverse micellar extraction is one such potential and a promising liquid-liquid extraction technique, which has received immense attention for isolation and purification of proteins/enzymes in the recent times. This technique is easy to scale-up and offers continuous operation. This review, besides briefly considering important physico-chemical and biological aspects, highlights the engineering aspects including mass transfer, mathematical modeling, and technology development. It also discusses recent developments in reverse micellar extraction such as affinity based separations, enzymatic reactions in reverse micelles coupled with membrane processes, reverse micellar extraction in hollow fibers, etc. Special emphasis has been given to some recent applications of this technique.