ENZYMATIC MODIFICATION OF A CHEMISORBED LIPID MONOLAYER

The selectivity and specificity of enzymes may be exploited to create chemically complex surfaces which are difficult or impossible to achie ve using classical synthetic chemistry. In this paper we discuss the p reparation of a chemisorbed lipid film on a silicon wafer and explore the activity of free phospholipase C (PLC) on that film. A carboxylic acid derivative of the lipid dimyristoylphosphatidylcholine (DMPC) was attached to an amino-terminal silane (EDA) via amide bond formation t o create an immobilized lipid layer (EDA-DMPC). Films were characteriz ed using X-ray photoelectron spectroscopy (XPS), secondary-ion mass sp ectrometry (SIMS), atomic force microscopy (AFM), X-ray reflectivity, and ellipsometry. Following treatment with the enzyme phospholipase C (PLC), which catalyzes the cleavage of the lipid headgroup at the glyc erol-phosphate ester bond, the lipid him was reanalyzed using the abov e techniques. Before analysis, nonspecifically adsorbed PLC was remove d with a 25% trifluoroethanol rinse. XPS and SIMS results of the clean ed films show nearly complete removal of the phosphate from the lipid layer, indicating enzymatic activity of the PLC on the chemisorbed lip id layer.