Penetration behavior of Vibrio cholerae hemolysin into (DMPC/cholesterol) mixed monolayer

The penetration behavior of Vibrio cholerae hemolysin (VCH) into a mixed monolayer, consisting of dimyristoyl phosphatidylcholine (DMPC) and cholesterol, was investigated by area–time measurements and atomic force microscope (AFM) observations. Time-dependence studies of the surface area at a constant surface pressure revealed that VCH caused a two-step expansion of the monolayer. On the second step, small dots (diameter ∼10 nm) assigned to VCH subunits were observed at the monolayer surface 1.1 × 104 s after injection of VCH solution into the subphase, indicating VCH penetration into the monolayer. Compression at a higher surface pressure prevented VCH penetration into the monolayer.