PHASE BEHAVIOUR OF DPPC MONOLAYERS AT THE AIR/WATER INTERFACE INFLUENCED BY ADSORPTION OF PROTEINS

摘要

Morphology of the mixed monolayers of distearoylphosphatidylcholine (DSPC), and dipalmitoylphosphatidylcholine (DPPC) with β-casein and β-lactoglobulin, respectively, formed by penetration of the protein from a water subphase into the spread lipid monolayer at the water surface was observed by a high resolution Brewster angle microscopy (BAM). The micrographs of DSPC and DPPC monolayers containing β-casein and p-lactoglobulin reveal the incorporation of protein into the lipid-covered surface in the lipid coexistence range. The two proteins show different miscibility of protein and lipid at the air/water interface. It has been found that the DPPC and DSPC in liquid state form homogeneous films with P-lactoglobulin, whereas DSPC and DPPC form heterogeneous layers. Fewer interactions have been concluded from the images of BAM for DPPC/β-casein monolayer as compared to the mixed DPPC/β-lactoglobulin films. The combination of BAM images and n-A isotherm measurements of these mixed monolayers indicate that the portion of protein is reduced with increasing surface pressure and is finally squeezed out from the lipid layers.