The Guava Nexin® Annexin V Assay offers a simple, reproducible, and reliable assessment of early apoptosis. The assay relies on the translocation of phosphatidyl serine (PS) to the outer surface of the cell membrane, an event often associated with the onset of apoptosis. A mix-and-read assay for monitoring externalization of PS through the binding of Annexin V to the exposed PS, the automated single-cell analysis assay is the choice for monitoring apoptosis due to its sensitivity and reproducibility. Annexin V is a calcium-dependent phospholipid binding protein with high affinity for phosphatidylserine (PS), a membrane component normally localized to the internal face of the cell membrane. Early in the apoptotic pathway, molecules of PS are translocated to the outer surface of the cell membrane where Annexin V can readily bind to them. The assay relies on a two-dye stategy: 1) Annexin V-PE to detect PS on the external membrane of apoptotic cells and 2) 7-AAD, a cell impermeant dye, as an indicator of membrane structural integrity. 7-AAD is excluded from live, healthy cells and early apoptotic cells, but permeates late-stage apoptotic and dead cells.
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