Catalyzes calcium-induced ATP-independent rapid bidirectional and non-specific distribution of phospholipids (lipid scrambling or lipid flip-flop) between the inner and outer leaflet of the plasma membrane resulting in collapse of the phospholipid asymmetry which leads to phosphatidylserine externalization on the cell surface (PubMed:32110987). Mediates calcium-dependent phosphatidylserine externalization and apoptosis in neurons via its association with TRPC5 (PubMed:32110987). Also exhibits magnesium-dependent nuclease activity against double-stranded DNA and RNA but not single-stranded DNA and can enhance DNA decatenation mediated by TOP2A (By similarity). Negatively regulates FcR-mediated phagocytosis in differentiated macrophages (PubMed:26745724). May contribute to cytokine-regulated cell proliferation and differentiation (PubMed:12010804). a 1,2-diacyl-sn-glycero-3-phosphocholine(in) = a 1,2-diacyl-sn-glycero-3-phosphocholine(out) a 1,2-diacyl-sn-glycero-3-phosphoethanolamine(in) = a 1,2-diacyl-sn-glycero-3-phosphoethanolamine(out) a 1,2-diacyl-sn-glycero-3-phospho-L-serine(in) = a 1,2-diacyl-sn-glycero-3-phospho-L-serine(out) Magnesium. Can also use zinc with lower efficiency. Forms homooligomers in the presence of calcium (By similarity). Interacts with ABL (By similarity). Interacts with RELT, RELL1 and RELL2 (By similarity). Interacts with OXSR1 in the presence of RELT (By similarity). Interacts with OCLN, TOP2A and TOP2B (By similarity). Interacts with TRPC1, TRPC4 and TRPC5 (PubMed:32110987). Localizes to the perinuclear region in the presence of RELT. Palmitoylation regulates its localization to the cell membrane or the nucleus; trafficking to the cell membrane is dependent upon palmitoylation whereas in the absence of palmitoylation, localizes to the nucleus. Highly expressed in kidney, lung, liver and bone marrow, slightly in spleen, heart and macrophage. Up-regulated by SCF/KITL and GCSF/CSF3. The N-terminal proline-rich domain (PRD) is required for phospholipid scramblase activity. The transmembrane domain is essential for membrane insertion, phospholipid scramblase activity and proper calcium-binding. Phosphorylation at Thr-170 by PKC/PKCD increases its phospholipid scramblase activity during both cell stimulation and apoptosis (By similarity). Phosphorylated by OXSR1 in the presence of RELT (By similarity). Palmitoylation is required for its phospholipid scramblase activity (By similarity). Palmitoylation regulates its localization to the cell membrane or the nucleus; trafficking to the cell membrane is dependent upon palmitoylation whereas in the absence of palmitoylation, localizes to the nucleus (By similarity). Participates in a chromosomal translocation that produces MMTRA1A which is leukemogenic to syngenic SL mice and athymic nude mice. Knockout newborn mice display a reduced granulocyte production (PubMed:12010804). Hematopoietic precursor cell from knockout mice display defective colony formation and impaired differentiation to mature granulocytes as stimulated by SCF/KITL and GCSF/CSF3 (PubMed:12010804). Belongs to the phospholipid scramblase family.