Effects of the interaction of porcine pancreatic lipase with AOT/isooctane reverse micelles on enzyme structure and function follow predictable patterns

Aerosol OT/isooctane reverse micelles were used to investigate the dependence of the lipolytic activity of porcine pancreatic lipase on surfactant concentration. Kinetic constants for the lipolytic reaction were measured in parallel with structural studies using protein fluorescence and circular dichroism (CD) spectroscopy. Km and kcat values decreased with increasing surfactant concentration at constant water to surfactant ratio (wo = 11.85) from 25 to 100 mM AOT. These data suggested an association of the lipase with the micellar membrane and an uncompetitive inhibition of lipase activity by AOT. Structure prediction based on far-UV CD spectral data demonstrated structural reorganization of porcine pancreatic lipase upon incorporation into reverse micelles that was characterized by a large increase in beta-sheet, a decrease in alpha-helix, and slight increases in the random and beta-turn elements of structure. Other spectral changes of the lipase upon incorporation into reverse micelles included a blue shift in the fluorescence emission maximum from 342 to 335 nm and a 2.2-fold increase in the fluorescence intensity. These structure-function changes seem to be characteristic for the incorporation of lipases in AOT/isooctane reverse micelles.