Effect of using a co-solvent in the preparation of surfactant-coated lipases on catalytic activity in organic media

Surfactant-coated lipases (from Candida cylindracea) were prepared in phosphate buffer (pH 6.9) containing a 2% (v/v) water-miscible organic solvent. The molecular structure of the surfactants used to coat the lipase strongly affected the esterification activity of the modified lipases in isooctane, while both the yield and the enzymatic activity were significantly influenced by the nature of the co-solvent used during the preparation. Although, in general, the most suitable co-solvents were found to be hydrophilic, especially ethanol and N,N-dimethylformamide (DMF), no definite correlation between solvent hydrophobicity (log P) and the properties of the surfactant-coated lipases was revealed. However, when a co-solvent which can dissolve a surfactant well was employed, the surfactant number attached to one lipase molecule tended to decrease and the yield was also lowered. Addition of dimethylsulfoxide (DMSO), formamide, or ethylene glycol to the lipase buffer solution during preparation led to substantial decreases in catalytic activity, even though the modified lipases were obtained in a good yield. This results suggests that these co-solvents affect the three- dimensional structure of the lipase, that is, the catalytic activity of surfactant-coated lipases in organic media may be chiefly determined during the preparation process in an aqueous solution.