. "At the endoplasmic reticulum (ER) membrane, phosphatidylserine synthase 1 (PTDSS1) converts phosphatidylcholine (PC) into phosphatidylserine (PS) by facilitating the exchange of L-Serine (L-Ser) with the choline (Cho) head group (Saito et al. 1998, Tomohiro et al. 2009)."^^ . . . .