Yasuo TAKAHASHI^1,2, Niklas BARK¹, Masataka KINJO² and Rudolf RIGLER¹

¹Medical Biochemistry and Biophysics, Karolinska Institute, Stockholm, S-171 77, Sweden
²Research Institute for Electronic Science, Hokkaido University, Sapporo 060-0812, Japan

(Received March 6, 2003; Accepted October 9, 2003)

Recent studies have revealed the importance of the lipid micro domain for signal transduction in cell membrane. To analyze the biophysical properties of the lipid micro domain at the single molecule level, we measured the diffusion of fluorescence probe in human red blood cell (RBC) membrane using fluorescence correlation spectroscopy (FCS). The value of diffusion constant of octadecyl rhodamine B chloride (R18), D = 4.7 x 10^-9 cm²/s, is close to that of phospholipid molecules in membrane. This indicates that the probed RBC with R18 could be a convenient model for analyzing membrane property under natural conditions. Using this model, we investigated how amyloid beta peptide (A-beta) interacts with plasma membrane. This paper demonstrates that A-beta was inserted into the phospholipid bilayer of the RBC membrane and predicts the existence of the micro domain, lipid raft, on this membrane by the heterologous insertion of A-beta.

Key words: fluorescence correlation spectroscopy, red blood cell, amyloid beta peptide, membrane, lipid raft