Specific volume and compressibility of bilayer lipid membranes with incorporated Na,K-ATPase.

Ultrasound velocimetry and densitometry methods were used to study the interactions of the Na,K-ATPase with the lipid bilayer in large unilamellar liposomes composed of dioleoyl phosphatidylcholine (DOPC). The ultrasound velocity increased and the specific volume of the phospholipids decreased with increasing concentrations of protein. These experiments allowed us to determine the reduced specific apparent compressibility of the lipid bilayer, which decreased by approx.