in Cellular Membranes

Phosphatidylserine (PS) is the most abundant negatively charged phos- pholipid in eukaryotic membranes. PS directs the binding of proteins that bear C2 or gamma-carboxyglutamic domains and contributes to the electrostatic association of polycationic ligands with cellular mem- branes. Rather than being evenly distributed, PS is found preferentially in the inner leaflet of the plasma membrane and in endocytic mem- branes. The loss of PS asymmetry is an early indicator of apoptosis and serves as a signal to initiate blood clotting. This review discusses the determinants and functional implications of the subcellular distribution and membrane topology of PS.