Detection of Phosphatidylserine Externalization During Apoptosis. Shailaja Kasibhatla et al. An early event in apoptosis is the externalization of phosphatidylserine (PS), a phospholipid normally restricted to the inner leaflet of the plasma membrane. This apoptotic event can be monitored using Annexin V, a PS-specific binding protein. This protocol uses Annexin V-FITC as a probe, but Annexin V-biotin is also available, and binding can be revealed using streptavidin-FITC or oth - [Read Detection Of Phosphatidylserine Externalization During Apoptosis (Subscription Required)]