The active site of Candida rugosa lipase (CRL) is mainly hydrophilic on its external face and hydrophobic on the internal side, and calix[n]arene-based surfactants form complexes with protein residues or with strong hydrogen bonds to open up the lid. Therefore, the activity of lipase persists for a long time. In this work, a series of cyclic and acyclic anionic surfactants (sodium dodecyl sulfate (SDS), p-sulfonatocalix[4]arene, and p-sulfonatocalix[8]arene) and zwitterionic surfactants (L-proline and L-proline derivative of calix[4]arene) were used to examine the relationship between the surfactants' molecular structures and their effects on the hydrolytic activity of CRL. We explored the effects of different surfactant concentrations, ring effects, and mixing times on CRL activity and several kinetic parameters. The results demonstrated that cyclic compounds were more effective than linear structures for increasing CRL activity and the highest enzyme activity was obtained by the addition of the calix[4]-L-proline derivative. This zwitterionic compound (calix[4]-L-proline derivative) maintains the active center of enzyme and conformation by enabling electrostatic interactions and hydrogen bonding with both the acidic and basic amino acid groups in the structure of the enzyme. The results indicated that, compared with the other surfactants, activating CRL with calix[4]-L-proline resulted in hyperactivation at all concentrations (a relative increase of 230%).
Keywords: Activity; Lipase; Surfactant; p-Sulfonatocalix[n]arene.