Electrostatics and reduction of dimensionality produce apparent cooperativity when basic peptides bind to acidic lipids in membranes.

The binding of pentalysine to phospholipid vesicles depends in a sigmoidal manner on the mole fraction of acidic lipid in the vesicles. A simple analysis demonstrates that this apparent cooperativity is probably due to both the reduction of dimensionality that occurs when the first basic residue binds to an acidic lipid in the membrane and the Boltzmann accumulation of the peptide in the electrostatic diffuse double layer produced by the charged lipids.