Figure 3. Contribution of phospholipid species to membrane composition and charge.

(A) Schematic representation of the lipid composition of the plasma membrane. The color of the headgroup not only identifies the different species, but is indicative of its charge. The relative mole ratio of the lipids is shown in parentheses. (B) Anionic lipids dictate electrostatic targeting of proteins during phagocytosis. The stages of phagocytosis from Figure 1 are shown, with the relative charge of membranes or ligand proteins illustrated by color. Note that the plasmalemma is most negative, and secretory membranes are least negative. The phagosome membrane has an intermediate negativity, and polycationic proteins are shown in varying shades according to their charges.