Liquid-liquid extraction of a recombinant protein with a reverse micelle phase

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.

Use of reverse micelles for the simultaneous extraction of oil, proteins, and glucosinolates from cruciferous oilseeds

Cruciferous oilseeds are important sources of oil, proteins, and glucosinolates (GLs), potentially available when biorefinery processes are used. The proposed extraction technology is based on the use of reverse micelles (RMs) made with cetyltrimethylammonium bromide (CTAB) dispersed in organic solvent. The physicochemical properties of this extraction system and the good water solubility of many high value compounds, such as GLs and some proteins, permit the simultaneous extraction of oil, and these products from cruciferous oilseed meals. This procedure is based on three main steps: (i) seed conditioning; (ii) solid-liquid extraction by RM solution; and (iii) back-transfer of the RM solution for recovery of the extracted compounds. The method makes it possible to simultaneously extract almost the same amount of oil as with pure organic solvents used in the current extraction plants and more than 90% of soluble proteins and GLs. It is a promising biorefinery technology alternative to traditional oil extraction processes.

Selective extraction and recovery of cytochrome c by liquid-liquid extraction using a calix[6]arene carboxylic acid derivative

Recently, we reported that a calix[6]arene carboxylic acid derivative can selectively extract the lysine-rich protein cytochrome c by interacting with amino groups on the protein surface. In the present article, quantitative extraction and recovery of cytochrome c using this calix[6]arene carboxylic acid derivative are described. Both adjustment of the pH under acidic conditions and addition of an alcohol are necessary to strip the extracted protein from an organic solution to an aqueous solution. Separation of cytochrome c and lysozyme using the calix[6]arene was achieved under the optimal conditions. In the forward extraction stage, 93% of the cytochrome c was extracted, while lysozyme remained in the solution. In the subsequent stripping stage, the extracted cytochrome c was quantitatively recovered in an aqueous solution. Finally, separation of these proteins, which have similar molecular weights and isoelectric points, was accomplished.

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.

Conformational transition and mass transfer in extraction of proteins by AOT--alcohol--isooctane reverse micellar systems

We examined quantitatively the effect of alcohols on protein and reverse micellar structure. We used circular dichroism (CD) to compare the effects of various alcohols on the protein structure, and percolation phenomena to evaluate the effects of various alcohols on reverse micellar structure. Upon the addition of alcohols to the bulk aqueous phase, proteins were denatured significantly, depending on the alcohol species and concentration, suggesting that use of alcohol directly to the stripping solution is not effective in back-extraction processes of proteins. In the present study, a new method, a small amount of alcohol is added to the surfactant-organic solution to improve the back-extraction behaviors of proteins. Practically, in the back-extraction process, the alcohols suppressing the cluster formation of reverse micelles (high value of beta1), remarkably improved the back-extraction behavior of proteins. In addition, the same alcohol molecules showed a positive effect on the rate and fraction of protein back-extraction. From a result of the CD measurement of the back-extracted proteins, it was known that the alcohols added to reverse micellar solution allowed the proteins to back-extract safely without causing structural changes. These results show that the values of beta(t), defined by the variation of percolation processes, and the back-extraction behaviors of proteins have a good relationship, suggesting that the back-extraction processes were controlled by the micellar-micellar and protein-micellar interactions.

Studies on the purification of peroxidase from horseradish roots using reverse micelles

Horseradish peroxidase (HRP) was successfully purified from horseradish roots by a two-stage reverse-micellar extraction from the dialyzed aqueous extract. The anionic surfactant AOT dissolved in isooctane was used to produce the reverse-micellar phases. The narrow pH range at which HRP solubilization occurred was exploited to remove most of the contaminant proteins in the first forward extraction. In the second extraction stage, HRP was selectively solubilized and concentrated by using a volume ratio of 10 between the aqueous and organic phases. The HRP final specific activity was 86 guaiacol U mg-1, obtained with a purification factor of 80 and yield of 46%. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed two overlapping bands, with HRP corresponding to that at 43.8 kDa. Image analysis on isoelectric focusing (IEF) gels showed that the HRP was 80% pure. Ion exchange liquid chromatography showed that most of the specific activity was due to the basic isoenzyme with pI 8.5, which comprises 33.5% of the product. There were high HRP losses as a precipitate at the interface when direct reverse-micellar extraction was attempted from the crude extract. It is believed that the hydrophobic environment near the haem group of the HRP basic isoenzyme favors complex formation with the surfactant, and that this is promoted at higher protein concentrations.

Liquid-liquid extraction of a recombinant protein with reverse micelles

Recombinant cytochrome b5 was extracted into the reversed micelle phase of an anionic surfactant (AOT) in octane and back-extracted to a final aqueous phase. The extraction of the protein was controlled by an electrostatic mechanism, since it was dependent on the global charge of the protein. This was directly demonstrated by experiments with native and mutant cytochromes obtained by site directed mutagenesis. The back-extraction of cytochrome b5 to a fresh aqueous phase was decreased by factors that reduced the size of the water pool of the organic phase, such as high salt concentrations (1-2 mol dm-3 NaCl) and low temperatures (4 degrees C), probably because of an increase in a favourable interaction of this protein with the surfactant at closer distances.