2.7.8.29	malfunction	gain-of-function mutation of PTDSS1 encoding phosphatidylserine synthase 1, a causative heterozygous missense mutations in gene PTDSS1, causes Lenz-Majewski syndrome (LMS), a syndrome of intellectual disability and multiple congenital anomalies that features generalized craniotubular hyperostosis. End-product inhibition of PSS1 by phosphatidylserine is markedly reduced in the mutant. The gain-of-function mutation is associated with regulatory dysfunction of PSS1. Phenotypes, overview	741056	
2.7.8.29	malfunction	mutation W277R of PTDSS1 encoding phosphatidylserine synthase 1 causes Lenz-Majewski hyperostotic dwarfism with hyperphosphoserinuria. Lenz-Majewski hyperostotic dwarfism (LMHD) is an ultra-rare Mendelian craniotubular dysostosis that causes skeletal dysmorphism and widely distributed osteosclerosis. In vivo, PTDSS1 defects cause LMHD and support enhanced biosynthesis of PTDS in the pathogenesis of LMHD, while in vitro, these PTDSS1 mutations are gain-of-function and increase PTDS production. Phenotype, overview	740791	
2.7.8.29	metabolism	link between phosphatidylserine synthesis and bone metabolism	741056	
2.7.8.29	metabolism	phosphatidylserine is synthesized in mammalian cells by two integral membrane proteins, PS synthase 1 and 2 (PSS1 and PSS2). These enzymes catalyze the formation of phosphatidylserine by an exchange reaction in which serine replaces the head group of the corresponding substrate phospholipids, phosphatidylcholine (PC) for isozyme PSS1 and phosphatidylethanolamine (PE) for isozyme PSS2	722906	
2.7.8.29	physiological function	docosahexaenoic acid positively modulates phosphatidylserine biosynthesis. Over-expression of PSS2 alters neither the phosphatidylserine level nor the effect of docosahexaenoic acid on phosphatidylserine increase	693711	
2.7.8.29	physiological function	expression of PSS2 in ethanolamine-requiring mutant Chinese hamster ovary cells defective in PSS1, reverses the ethanolamine auxotrophy. However, the phosphatidylethanolamine content is not normalized unless the culture medium is supplemented with ethanolamine. In both mutant chinese hamster ovary cells and hepatoma cells transfected with PSS2 cDNA the rate of synthesis of phosphatidylserine and phosphatidylserine-derived phosphatidylethanolamine does not exceed that in parental chinese hamster ovary cells or control McArdle cells, respectively. Expression of murine PSS2 in McArdle cells does not inhibit phosphatidylethanolamine synthesis via the CDP-ethanolamine pathway, whereas expression of similar levels of PSS1 activity inhibit this pathway by approx. 50%	717208	
2.7.8.29	physiological function	expression of PSS2 is necessary for normal growth of procyclic trypanosomes and PSS2 represents the unique route for phosphatidylserine formation in Trypanosoma brucei. Downregulation of TbPSS2 by RNAi for 3 days inhibits incorporation of serine into newly synthesized phosphatidylserine by 94.8	-, 748671	
2.7.8.29	physiological function	induced apoptosis with staurosporine in four Chinese hamster ovary cell lines that are deficient in PSS1, EC 2.7.8.8, and/or PSS2. In all cell lines, regardless of their content of PSS1 and/or PSS2, apoptosis occurrs to approximately the same extent, and within approximately the same time frame, as in parental CHO-K1 cells. Cells that are deficient in either PSS1 or PSS2, as well as cells that are deficient in both PSS1 and PSS2, externalize normal amounts of phosphatidylserine	661228	
2.7.8.29	physiological function	intercrosses of mice lacking PSS1, EC 2.7.8.8, and PSS2-/- mice yield mice with three disrupted Pss alleles but no double knockout mice. In PSS1-/-PSS2+/- and PSS1+/-PSS2-/- mice, serine exchange activity is reduced by 65-91%,and the tissue content of phosphatidylserine and phosphatidylethanolamine is also decreased. Elimination of either PSS1 or PSS2, but not both, is compatible with mouse viability, mice can tolerate as little as 10% of normal total serine-exchange activity, and mice survive with significantly reduced phosphatidylserine and phosphatidylethanolamine content	693046	
2.7.8.29	physiological function	introduction of the pssB cDNA into CHO-K1 cells results in striking increases in both the serine and ethanolamine base exchange activities. The pssB cDNA is incapable of increasing the choline base exchange activity. The expression of the pssB gene in Sf9 insect cells also results in striking increases in both serine and ethanolamine base exchange activities. The pssB cDNA transforms a phosphatidylserine-auxotrophic mutant of CHO-K1 cells lacking PSS I, EC 2.7.8.8, to phosphatidylserine prototrophy. The phosphatidylserine content of the resultant transformant grown without exogenous phosphatidylserine for 2 days is 4-fold that of the mutant and similar to that of CHO-K1 cells, indicating that the pssB cDNA complements the phosphatidylserine biosynthetic defect of the PSS I-lacking mutant	717758