SHAPES OF BILAYER VESICLES WITH MEMBRANE EMBEDDED MOLECULES

The interdependence of the lateral distribution of molecules which are embedded in a membrane (such as integral membrane proteins) and the s hape of a cell with no internal structure (such as phospholipid vesicl es or mammalian erythrocytes) has been studied. The coupling of the la teral distribution of the molecules and the cell shape is introduced b y considering that the energy of the membrane embedded molecule at a g iven site of the membrane depends on the curvature of the membrane at that site. Direct interactions between embedded molecules are not cons idered. A simple expression for the interaction of the membrane embedd ed molecule with the local membrane curvature is proposed. Starting fr om this interaction, the consistently related expressions for the free energy and for the distribution function of the embedded molecules ar e derived. The equilibrium cell shape and the corresponding lateral di stribution of the membrane embedded molecules are determined by minimi zation of the membrane free energy which includes the free energy of t he membrane embedded molecules and the membrane elastic energy. The re sulting inhomogeneous distribution of the membrane embedded molecules affects the cell shape in a nontrivial manner. In particular, it is sh own that the shape corresponding to the absolute energy minimum at giv en cell volume and membrane area may be elliptically non-axisymmetric, in contrast to the case of a laterally homogeneous membrane where it is axisymmetric.