Catalyzes a base-exchange reaction in which the polar head group of phosphatidylethanolamine (PE) or phosphatidylcholine (PC) is replaced by L-serine (PubMed:1748687, PubMed:3084470, PubMed:9539713). Catalyzes mainly the conversion of phosphatidylcholine (PubMed:1748687, PubMed:3084470, PubMed:9539713). Also converts, in vitro and to a lesser extent, phosphatidylethanolamine (PubMed:1748687, PubMed:3084470, PubMed:9539713). 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 Inhibited by exogenous phosphatidylserine. Phospholipid metabolism; phosphatidylserine biosynthesis. Highly enriched in the mitochondria-associated membrane (MAM). Belongs to the phosphatidyl serine synthase family.