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Protein-lipid interactions play a decisive role in the architecture of the cell membrane structure. They can be used to explain molecular mechanisms of various membrane processes, such as energy transmission and conversion, mechanoreception, etc. The study of interactions of integral proteins with the lipid bilayer is of the special interest. Integral proteins, namely their hydrophobic parts, are immersed into the membrane. Due to differences in the length of the hydrophobic moieties of the proteins and the hydrocarbon chains of the lipids, as well as to the action of electrostatic and mechanical forces, regions of changed lipid bilayer structure arise in the environment of a protein. These areas may change upon conformational changes of a protein. A number of questions arise in studying protein-lipid systems, e.g., 1 . How do physical and structural characteristics of lipid bilayer change upon the incorporation of integral proteins and during conformational changes of the latters? 2. What are the dimensions of changed membrane structure regions in the environment of a protein? 3. How is the temporal stability of the structural changes? To approach the above problems, mechanical and thermodynamical characteristics of bilayer lipid membranes (BLM) and large unilamellar liposomes (LUV, diameter approx. 100 nm) with incorporated integral proteins (bacteriorhodopsin, BR, and hormonal receptors for insulin, HR) were studied. Also, mechanical characteristics of membrane were studied during conformational changes of BR (in the dark and induced by light) and HR (under the action of insulin and its antagonist glucagon). The electrostriction method of measurement of modulus of elasticity in the direction normal to the membrane plane, E was used together with differential scanning calorimetry (DSC)2 and differential ultrasonic velocimetry (DUV).3
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