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There are numerous advantages of employing enzymes as catalysts in organic solvents or aqueous solutions containing organic solvents instead of water. A few natural enzymes which are stable in the presence of organic solvents have been discovered. However, almost all natural enzymes are easily denatured and inactivated in the presence of organic solvents. Therefore, several physical and chemical methods, such as immobilization, modification, and entrapment, for stabilizing enzymes in the presence of organic solvents were developed. Protein engineering using site directed mutagenesis and directed evolution are useful for clarifying why organic solvent-stable enzymes are stable in the presence of organic solvents and for developing organic solvent-stable mutant enzymes.

An organic solvent-stable protease (PST-01 protease) in a culture broth of organic solvent-tolerant Pseudomonas aeruginosa PST-01 was purified by successive hydrophobic interaction chromatography using Butyl-Toyopearl gels. The purified enzyme was homogeneous as determined by SDS-polyacrylamide gel electrophoresis. PST-01 protease had a molecular mass of 38 kDa. The optimum temperature and pH for casein hydrolysis were 55 degrees C and 8.5, respectively. PST-01 protease was stable at pH 8-12 and below 50 degrees C and was determined to be a metalloprotease which was inhibited by EDTA, 1,10-phenanthroline, and phosphoramidon. PST-01 protease inhibited by EDTA was reactivated completely by the addition of zinc or cobalt ions. The stability of PST-01 protease in solutions containing water-soluble organic solvents or alcohols was higher than that in the absence of organic solvent. Furthermore, in general, PST-01 protease was more stable than commercially available proteases, namely, subtilisin Carlsberg, thermolysin, and alpha-chymotrypsin, in the presence of water-soluble organic solvents or alcohols.

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A model was proposed for simulation of a particle formation stage in the dispersion polymerization of styrene in ethanol. The role of poly(N-vinylpyrrolidone) molecules grafted by a polystyrene oligomer (PVP-g-PS) was taken into consideration for the particle stabilization. The model was derived based on the following mechanism: (i) polystyrene molecules whose degree of polymerization is greater than j cr precipitate and form particles, (ii) particle aggregation due to the Brownian diffusion and the shear stress of the fluid continues until the amount of the PVP-g-PS molecules is enough to cover all the particle surface, and (iii) particles do not aggregate with each other once the entrire particle surface is covered with the PVP-g-PS molecules. The theoretical particle concentrations calculated using the present model under various monomer concentrations and stirring speeds were in good agreement with the experimental data.