Catalyzes the formation of phosphatidylethanolamine (PtdEtn) from phosphatidylserine (PtdSer). Plays a central role in phospholipid metabolism and in the interorganelle trafficking of phosphatidylserine (PubMed:7890740, PubMed:7890739, PubMed:24366873). Phosphatidylethanolamine produced by PSD2 is insufficient to completely provide the PtdEtn pool required by mitochondria under respiratory conditions (PubMed:11294902). PSD2 is also involved in the PtdSer transport step to the site of PtdEtn synthesis on the Golgi/endosome membranes (PubMed:24366873). Required for normal heavy metal resistance (PubMed:20016005). a 1,2-diacyl-sn-glycero-3-phospho-L-serine + H(+) = a 1,2-diacyl-sn-glycero-3-phosphoethanolamine + CO2 Binds 1 pyruvoyl group covalently per subunit. Phospholipid metabolism; phosphatidylethanolamine biosynthesis; phosphatidylethanolamine from CDP-diacylglycerol: step 2/2. Heterodimer of a large membrane-associated beta subunit and a small pyruvoyl-containing alpha subunit (By similarity). Interacts with pstB2/PDR17 (PubMed:20016005, PubMed:24366873). This interaction may be a means to structurally tether the donor membrane (ER) harboring PstB2/PDR17 to acceptor membranes (Golgi/endosomes) harboring PSD2 during PtdSer transport to the site of PtdEtn synthesis (PubMed:24366873). The C2 domains have an essential, but non-catalytic function (Probable) (PubMed:24366873). Both C2-1 and C2-2 facilitate interaction with PstB2/PDR17 and are required for lipid transport function (PubMed:24366873). Is synthesized initially as an inactive proenzyme. Formation of the active enzyme involves a self-maturation process in which the active site pyruvoyl group is generated from an internal serine residue via an autocatalytic post-translational modification. Two non-identical subunits are generated from the proenzyme in this reaction, and the pyruvate is formed at the N-terminus of the alpha chain, which is derived from the carboxyl end of the proenzyme. The autoendoproteolytic cleavage occurs by a canonical serine protease mechanism, in which the side chain hydroxyl group of the serine supplies its oxygen atom to form the C-terminus of the beta chain, while the remainder of the serine residue undergoes an oxidative deamination to produce ammonia and the pyruvoyl prosthetic group on the alpha chain. During this reaction, the Ser that is part of the protease active site of the proenzyme becomes the pyruvoyl prosthetic group, which constitutes an essential element of the active site of the mature decarboxylase. Belongs to the phosphatidylserine decarboxylase family. PSD-B subfamily. Eukaryotic type II sub-subfamily.