Catalyzes a base-exchange reaction in which the polar head group of phosphatidylethanolamine (PE) or phosphatidylcholine (PC) is replaced by L-serine (By similarity). Catalyzes mainly the conversion of phosphatidylcholine but also converts, in vitro and to a lesser extent, phosphatidylethanolamine (By similarity). a 1,2-diacyl-sn-glycero-3-phosphoethanolamine + L-serine = a 1,2-diacyl-sn-glycero-3-phospho-L-serine + ethanolamine a 1,2-diacyl-sn-glycero-3-phosphocholine + L-serine = a 1,2-diacyl-sn-glycero-3-phospho-L-serine + choline Phospholipid metabolism; phosphatidylserine biosynthesis. Highly enriched in the mitochondria-associated membrane (MAM). Belongs to the phosphatidyl serine synthase family.