MCE Annexin V-EGFP/PI Apoptosis Detection Kit provides a rapid and convenient method to detect cell apoptosis and necrosis. In normal live cells, Phosphatidylserine (PS) is located on the cytoplasmic surface of the cell membrane. Upon initiation of apoptosis, PS translocates from the inner to the outer leaflet of the membrane. Annexin V is a 35-36 kDa Ca2+ - dependent phospholipid-binding protein that has a high affinity for PS. Annexin V labeled with green fluorescent EGFP can identify apoptotic cells by binding to PS exposed on the outer leaflet. Propidium Iodide (PI) is a cell-membrane impermeable dye to live cells and early apoptosis cells, but stains late apoptosis cells and necrosis cells with red fluorescence. After staining, live cells show little or no fluorescence (Annexin V-/PI-), early apoptosis cells show green fluorescence (Annexin V+/PI-), late apoptosis cells and necrosis cells show red and green fluorescence (Annexin V+/PI+).