Phosphatidylserine (PS) accounts for 5 to 10% of cell membrane phospholipids. In addition to its role as a structural component, PS is involved in cell signaling, blood coagulation, and apoptosis. PS is synthesized by a calcium-dependent base-exchange reaction catalyzed by PS synthases (EC 2.7.8.8), like PTDSS1, that exchange L-serine for the polar head group of phosphatidylcholine (PC) or phosphatidylethanolamine (PE) (Sturbois-Balcerzak et al., 2001 [PubMed 11084049]).[supplied by OMIM, May 2009].
Stone, Vance: "Phosphatidylserine synthase-1 and -2 are localized to mitochondria-associated membranes." in: The Journal of biological chemistry, Vol. 275, Issue 44, pp. 34534-40, (2000) (PubMed).