ApoScreen? Annexin V (SB Cat. No. 10039) is a recombinant protein that is expressed in eukaryotic cells. A number of changes in cell structure occur during apoptosis. One major change is the loss of membrane phospholipid asymmetry, with translocation of phosphatidylserine (PS) from the inner leaflet of the phospholipid bilayer to the external surface. Annexin V, a member of the annexin family of calcium-dependent phospholipid binding proteins, has a high affinity for phosphatidylserine (PS)-containing phospholipid bilayers. Conjugated Annexin V can be used to monitor changes in cell membrane phospholipid asymmetry, thereby providing a convenient tool for detection of apoptotic cells.