May mediate accelerated ATP-independent bidirectional transbilayer migration of phospholipids upon binding calcium ions that results in a loss of phospholipid asymmetry in the plasma membrane. May play a central role in the initiation of fibrin clot formation, in the activation of mast cells and in the recognition of apoptotic and injured cells by the reticuloendothelial system. Interacts with PDCD6. Expressed in heart, brain, placenta, lung, liver, kidney, pancreas, spleen, thymus, prostate, testis, uterus, small intestine and colon. Not detected in peripheral blood lymphocytes. The N-terminal proline-rich domain (PRD) is required for phospholipid scramblase activity. Belongs to the phospholipid scramblase family.