ABSTRACT
This chapter begins with emphasis on the factors influencing lipid asymmetry including transmembrane dislocation of lipid molecules. The transmembrane distribution of lipids depends on a large number of diverse factors that can be divided into two main groups: physical factors and factors of biosynthesis and catabolism. The chapter discusses critically the main techniques which are used in studies of lipid asymmetry and evaluates their possibilities and limitations. The topological asymmetry of lipids influences a great number of membrane properties and functions, such as charge distribution, ion fluxes, enzyme activities, binding of external molecules. Determination of the transversal distribution of lipids in artificial or biological membranes is based on the application of different probes or immunochemical procedures. Experiments performed with model systems have demonstrated that in pure lipid systems the flip-flop rate depends on numerous physico-chemical factors including the structure, phase behavior of the lipids, presence of lipid peroxidation products, and of phospholipids species which tend to form nonbilayer structures.
