Phospholipid scramblase 3 is an enzyme that in humans is encoded by the PLSCR3 gene[5][6] (abbreviated to PLS3 in this section). Like the other phospholipid scramblase family members (PLS1, PLS2, PLS4), PLS3 is a type II plasma membrane protein that is rich in proline and integral in apoptosis, or programmed cell death. The regulation of apoptosis is critical for both cell development and tissue homeostasis. Although phospholipid scramblase is thought to exist in all eukaryotic cells, PLS3 is a protein that is novel to the mitochondria. This is very important because mitochondria are central in the apoptotic cell pathway. This newly found member of the scramblase family is "responsible for phospholipid translocation between two lipid compartments", the inner mitochondrial membrane and the outer membrane. Further experimental evidence suggests that the mechanism and effectors of PLS3's enzymatic activity are rather nuanced.