Reverse Micelle Extraction

The extraction and purification of proteins using reversed phase micelle systems has been the subject of extensive study in recent years (Luisi, 1985; Martinek et al, 1986; Fletcher and Parrot, 1988; Krei and Hustedt, 1992; Matzke etal, 1992). Reverse micelles are aggregates of surfactant molecules in organic solvents. The polar head groups of the surfactant are directed towards the interior of the micelle and form a polar core which can solubilize water and hence the proteins, while the lipophilic chains are exposed to the organic solvent. Figure 7 shows a schematic diagram of protein solubilization using reverse micelles. Here an electrolyte/protein solution is contacted with an organic solvent containing oil-soluble surfactant. After the mixture is vigorously shaken and interphase equilibrium is achieved, the phases are separated by centrifugation. When a double tailed

Figure 7. Schematic diagram of the phase transfer process for solubilization in reversed micelles

surfactant such as AOT (2-diethylhexyl sulfosuccinate or Aerosol-OT) is used with electrolyte in the aqueous phase, a water-in-oil (W/O) microemulsion is formed. This is also favoured by addition of long chain alcohols and increase in temperature.

The greatest advantage of using reverse micelles to solubilize proteins is that the proteins can be used in apolar solvents. Thus, enzymes have been encapsulated inside the water cores of reverse micelles with retention of catalytic activity (Barbaric and Luisi, 1981; Levashov et al, 1982; Fletcher et al, 1984). Table 8 illustrates some of the recently reported work on protein solubilization using reverse micelle extraction.

Table 8

Some recent studies on reverse micelle extraction of proteins

Table 8

Some recent studies on reverse micelle extraction of proteins

Protein/Enzyme

System

Reference

Horse liver alcohol dehydrogenase (HLADH)

SDS & Cetyltrimethyl-ammonium bromide (CTAB)

Samana et al (1984)

Lysozyme

Iso-octane/AOT

Steinmann et al (1986)

Lysozyme

Chloroform/CTAB

ibid

Lysozyme

Iso-octane/Tetraethylene glycol dodecyl ether

ibid

Beta-hydroxy butyrate dehydrogenase

Iso-octane-hexanol/CTAB

Giovenco et al (1987)

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