ApoScreen? Annexin V Apoptosis Kit-PE (SB Cat. No. 10010-09) employs a R-phycoerythrin-conjugated Annexin V (Annexin V-PE) in concert with 7-Aminoactinomycin D (7-AAD) to evaluate subpopulations of cells undergoing apoptosis. During the early stages of apoptosis, cells begin to display phosphatidylserine (PS) on the outer cell membrane where it is readily detectable by staining the cells with Annexin V-PE. As the plasma membrane becomes increasingly permeable during the later stages of apoptosis, 7-AAD can readily move across the cell membrane and bind to cellular DNA, providing a means for identifying those cells that have lost membrane integrity through mechanisms including necrosis. When cells are double stained with Annexin V-PE and 7-AAD, three different cell populations may be observed - (i) live cells that do not stain with either Annexin V-PE or 7-AAD; (ii) necrotic cells that stain with both reagents; and (iii) apoptotic cells that stain with Annexin V-PE only. Analysis may be performed on any flow cytometer equipped with a single laser using excitation at 488 nm.