Lipase Activity on Lipid/Polymer Binary Monolayers: Lateral Diffusion-Controlled Enzyme Kinetics

Abstract

This is a follow-up study to our recent reports of lipase catalysis on uniphasic binary monolayers of L-α-dilauroylphosphatidylcholine (DLPC) and cholesterol. The earlier studies were undertaken to show that the reaction kinetics on monolayers of ester hydrolysis catalyzed by an interface active enzyme, lipase, is closely correlated to the lateral dynamics, i.e., the hydrolysis of a lipase substrate is a diffusion-controlled process, whereby the rates were quantitatively analyzed in terms of a theory of purely two-dimensional diffusion-controlled reactions. In so establishing, cholesterol was used as the second component to retard the lateral diffusion coefficient of DLPC to different extents. On the other hand, phospholipids and cholesterol are being found to form “condensed complexes” even in homogeneous monolayers, hence the finding of the diffusion-controlled processes might well be construed to be unique to the phospholipid-cholesterol system. To show that the diffusion-controlled reaction kinetics o...