{"id":"149957ee-e1fa-58aa-ac31-00b6e0b01570","stable_key":"649e861b-265a-5912-bc36-3a73e53ef892:l-serine-pss2-exchange","predicate":"uses_serine_to_make","statement":"Purified human PSS2 converted phosphatidylethanolamine, but not phosphatidylcholine, into phosphatidylserine; added phosphatidylserine inhibited purified PSS2.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"context_dependent","is_public":true,"mechanism_event_id":"0b9098b7-6e59-5000-859e-2eb19cb73bf1","mechanism_event_label":"A second enzyme uses a different membrane-lipid starting material.","subject":{"id":"59772b14-d105-5321-9adc-13d952c379e4","slug":"ptdss2","display_name":"Human phosphatidylserine synthase 2 / PTDSS2","entity_type_key":"protein"},"object":{"id":"0e2dd859-6135-556e-938f-d177f1e8c1ad","slug":"phosphatidylserine","display_name":"Phosphatidylserine","entity_type_key":"lipid"},"evidence_count":1,"mechanism_event":{"id":"0b9098b7-6e59-5000-859e-2eb19cb73bf1","stable_key":"649e861b-265a-5912-bc36-3a73e53ef892:l-serine-pss2-exchange-event","event_type":"observed_relationship","label":"A second enzyme uses a different membrane-lipid starting material.","description":"Purified human PSS2 converted phosphatidylethanolamine, but not phosphatidylcholine, into phosphatidylserine; added phosphatidylserine inhibited purified PSS2.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"59772b14-d105-5321-9adc-13d952c379e4","slug":"ptdss2","display_name":"Human phosphatidylserine synthase 2 / PTDSS2","entity_type_key":"protein"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"0e2dd859-6135-556e-938f-d177f1e8c1ad","slug":"phosphatidylserine","display_name":"Phosphatidylserine","entity_type_key":"lipid"},"role":"target","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"c882cd0b-9d83-5b07-bd1c-fe4d45657dcb","slug":"l-serine","display_name":"L-Serine","entity_type_key":"small_molecule"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"be4a52f4-f31c-59b7-b0da-4178fbb069c8","slug":"phosphatidylethanolamine","display_name":"Phosphatidylethanolamine","entity_type_key":"lipid"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""},{"entity":{"id":"2f77ef6d-3ecd-5a80-9ca3-3cbea403d9fc","slug":"phosphatidylcholine","display_name":"Phosphatidylcholine","entity_type_key":"lipid"},"role":"context_participant","stoichiometry":null,"state_label":"","sequence_order":4,"notes":""}]},"contexts":[{"dimension":"evidence_access","value_text":"Primary abstract","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Purified epitope-tagged human PSS1/PSS2 substrate and feedback assays.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"In this preparation PSS1 used both PC and PE and was not inhibited by added PS; purified-enzyme feedback cannot be assumed identical across preparations or intact cells.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"L-Serine collection; species, compartment, exposure, co-substrates and manipulation remain explicit.","comparator":null,"unit":null,"notes":"","entity":{"slug":"l-serine","display_name":"L-Serine","entity_type_key":"small_molecule"}},{"dimension":"plain_language","value_text":"A second enzyme uses a different membrane-lipid starting material.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"Purification and characterization of human phosphatidylserine synthases 1 and 2. · 2009 · https://pubmed.ncbi.nlm.nih.gov/19014349/ · DOI 10.1042/BJ20081597","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"d741e982-f69d-587d-8734-89f57a5b1b68","evidence_kind":"source_excerpt","locator":"Lines 414-420","start_line":414,"end_line":420,"excerpt":"## l-serine-pss2-exchange\nA second enzyme uses a different membrane-lipid starting material.\nPurified human PSS2 converted phosphatidylethanolamine, but not phosphatidylcholine, into phosphatidylserine; added phosphatidylserine inhibited purified PSS2.\nModel: Purified epitope-tagged human PSS1/PSS2 substrate and feedback assays.\nLimitations: In this preparation PSS1 used both PC and PE and was not inhibited by added PS; purified-enzyme feedback cannot be assumed identical across preparations or intact cells.\nEvidence access: Primary abstract\nPurification and characterization of human phosphatidylserine synthases 1 and 2. · 2009 · https://pubmed.ncbi.nlm.nih.gov/19014349/ · DOI 10.1042/BJ20081597","model_system":"Purified epitope-tagged human PSS1/PSS2 substrate and feedback assays.","directness":"reported_statement","verification_status":"source_derived_draft","notes":"Original curation paraphrase; evidence access and experimental limitations specified.","relationship":"supports","weight":1.0,"link_notes":"","source":{"id":"70bcf57a-36bb-563f-9073-2d616e5f155a","stable_key":"import-649e861b-265a-5912-bc36-3a73e53ef892","title":"L-Serine: synthesis, one-carbon metabolism, lipids and cross-nutrient mechanisms (2026-09-19)","document_type":"imported_text","citation_label":"AI-assisted research curation; primary references, access levels and experimental limitations individually identified. 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