Catalyzes a base-exchange reaction in which the polar head group of phosphatidylethanolamine (PE) or phosphatidylcholine (PC) is replaced by L-serine (PubMed:10432300, PubMed:10938271, PubMed:23071296, PubMed:12361952). Catalyzes the conversion of phosphatatidylethanolamine and does not act on phosphatidylcholine (PubMed:10938271, PubMed:23071296). Can utilize both phosphatidylethanolamine (PE) plasmalogen and diacyl PE as substrate and the latter is six times better utilized, indicating the importance of an ester linkage at the sn-1 position (PubMed:23071296). Although it shows no sn-1 fatty acyl preference, exhibits significant preference towards docosahexaenoic acid (22:6n-3) compared with 18:1 or 20:4 at the sn-2 position (PubMed:23071296). a 1,2-diacyl-sn-glycero-3-phosphoethanolamine + L-serine = a 1,2-diacyl-sn-glycero-3-phospho-L-serine + ethanolamine 1-hexadecanoyl-2-(9Z-octadecenoyl)-sn-glycero-3-phosphoethanolamine + L-serine = 1-hexadecanoyl-2-(9Z-octadecenoyl)-sn-glycero-3-phospho-L-serine + ethanolamine 1-hexadecanoyl-2-(4Z,7Z,10Z,13Z,16Z,19Z-docosahexaenoyl)-sn-glycero-3-phosphoethanolamine + L-serine = 1-hexadecanoyl-2-(4Z,7Z,10Z,13Z,16Z,19Z-docosahexaenoyl)-sn-glycero-3-phosphoserine + ethanolamine 1-octadecanoyl-2-(5Z,8Z,11Z,14Z)-eicosatetraenoyl-sn-glycero-3-phosphoethanolamine + L-serine = 1-octadecanoyl-2-(5Z,8Z,11Z,14Z)-eicosatetraenoyl-sn-glycero-3-phosphoserine + ethanolamine 1-octadecanoyl-2-(4Z,7Z,10Z,13Z,16Z,19Z-docosahexaenoyl)-sn-glycero-3-phosphoethanolamine + L-serine = 1-octadecanoyl-2-(4Z,7Z,10Z,13Z,16Z,19Z-docosahexaenoyl)-sn-glycero-3-phosphoserine + ethanolamine 1-(1Z-octadecenyl)-2-(4Z,7Z,10Z,13Z,16Z,19Z-docosahexaenoyl)-sn-glycero-3-phosphoethanolamine + L-serine = 1-(1Z-octadecenyl)-2-(4Z,7Z,10Z,13Z,16Z,19Z-docosahexaenoyl)-sn-glycero-3-phospho-L-serine + ethanolamine 1-octadecanoyl-2-(9Z-octadecenoyl)-sn-glycero-3-phosphoethanolamine + L-serine = 1-octadecanoyl-2-(9Z-octadecenoyl)-sn-glycero-3-phospho-L-serine + ethanolamine 1-(1Z-octadecenyl)-2-(9Z-octadecenoyl)-sn-glycero-3-phosphoethanolamine + L-serine = 1-(1Z-octadecenyl)-2-(9Z-octadecenoyl)-sn-glycero-3-phospho-L-serine + ethanolamine 1-(1Z-octadecenyl)-2-(5Z,8Z,11Z,14Z- eicosatetraenoyl)-sn-glycero-3-phosphoethanolamine + L-serine = 1-(1Z-octadecenyl)-2-(5Z,8Z,11Z,14Z-eicosatetraenoyl)-sn-glycero-3-phospho-L-serine + ethanolamine Almost complete inhibition by ethanolamine in both the mitochondria-associated membrane (MAM) and endoplasmic reticulum (ER) per se. Phospholipid metabolism; phosphatidylserine biosynthesis. Highly enriched in the mitochondria-associated membrane (MAM). Highly expressed in testis. Detected at lower levels in kidney and heart. Null mice exhibit a reduction of more than 95% in serine exchange in testis and approximately 90% reduction in brain and liver. Testis weight is reduced and some animals are infertile. Elimination of either Pss1 or Pss2, but not both, is compatible with mouse viability. Mice can tolerate as little as 10% serine-exchange activity and are viable with small amounts of phosphatidylserine and phosphatidylethanolamine content. Belongs to the phosphatidyl serine synthase family.