Phosphatiylserine (PS or PtdSer) is a phospholipid nutrient found in fish, green leafy vegetables, soybeans, and rice, and is essential for the normal functioning of neuronal cell membranes, activating protein kinase C (PKC), which has been shown to be involved in memory function. Phosphatidylserine is usually kept on the inner-leaflet of cell membranes by an enzyme called translocase. In apoptosis, caspase 3 activation culminates in deactivation of translocase and activation of scramblase, which allows free movement of PtdSer down its concentration gradient, and activation of flippase, which transports PtdSer to the outer-leaflet of the plasma membrane. This is part of the process by which the cell is targeted for phagocytosis.