Imidazolium based ionic liquid type surfactant improves activity and thermal stability of lipase of Rhizopus oryzae

Abstract

Lipase and surfactant together form a potent pair in various biotransformation, industrial application and biotechnological studies. The present investigation deals with changes in the activity, stability and structure of lipase from Rhizopus oryzae NRRL 3562 in presence of long chain ionic liquid-type imidazolium surfactant. Both the activity and stability were found to be enhanced in presence of the surfactant at low concentration (1–125 μM) followed by inhibition at high concentration. The activity increased by 80% and thermal deactivation temperature raised by 2.5 °C. Investigations by ultraviolet–visible spectroscopy and circular dichroism revealed structural changes leading to rise in β-sheet content and lowering of α-helix at low surfactant concentrations. Deactivation at high concentration correlated with greater structural changes depicted by spectroscopic studies. Isothermal titration calorimetric studies showed the binding to be spontaneous in nature involving non-covalent interactions. High negative value of entropy signifies exposure of hydrophobic domains and increase in structural rigidity, which correlates with active site being more accessible and rigid in presence of the surfactant. Application of these surfactants hold greater potential in the field of lipase based biotransformations, enzyme structural modifications and studies.