Phospholipid Exchange Proteins (PEP) Move Lipids From ER to Peroxisomes, Plastids and Mitochondria
Shown to the right is an animation which illustrates how cytoplasmic PEP move lipids from the site of lipid synthesis in the ER to the membranes which are not part of the endomembrane system and which therefore do not have another source of membrane lipids. The cell has several different PEPs, one for each type of lipid which must be mobilized and moved around the cell. The PEPs pluck phospholipids out of one membrane and then deliver it to a different cellular membrane at random. They can remove or insert their specific phospholipid into any membrane. But, in the cell, the overall concentration of membrane phospholipids is greatest in the ER where the phospholipids are being synthesized. Thus, there is net movement of phospholipids from the membranes where they are most concentrated (the ER) to those membranes which have proportionately less membrane (eg: the peroxisome or mitochondrial membranes).