Bioconversion of Lipophilic or Water Insoluble Compounds by Immobilized Biocatalysts in Organic Solvent Systems

Abstract

Enzymes and microbial cells were entrapped inside gels of optionally hydrophobic or hydrophilic character as well as network structure by using prepolymers of photo-crosslinkable resins or urethane resins. Biocatalysts so immobilized were used for successful bioconversion of various highly lipophilic or water-insoluble compounds in water-organic co-solvent systems or water-saturated organic solvents. The influence of the hydrophobicity and the net work structure of the gels and the polarity of the solvents were studied in terms of the catalytic activity and operational stability of the gel-entrapped biocatalysts. In a less-polar solvent system, the hydrophobicity of the gels used to entrap microbial cells or enzyme affected markedly the catalytic activity of the gel-entrapped biocatalysts. The use of hydrophobic gels is preferable for bioconversion of highly lipophilic compounds. The activity of gel-entrapped cells correlated closely with the partition of substrates between the gels and external solvents. Bioconversion of steroids and terpenoid in organic solvents could be achieved successfully by gel-entrapped microbial cells whose stability was improved by immobilization. The selection of suitable gel hydrophobicity makes it possible to control conversion routes in reactions involving two or more reactants of different hydrophobicity. Synthesis of water-insoluble compounds, such as adenine arabinoside from uracil arabinoside and adenine, was catalyzed by entrapped bacterial cells which showed an excellent stability in a water-organic co-solvent system. Furthermore, lipase adsorbed on Celite and then entrapped in a hydrophobic gel, revealed high activity and good stability in the ester exchange reaction of triglyceride.