Minor apolipoprotein mainly associated with HDL and to a lesser extent with VLDL. May also be associated with chylomicrons. Important determinant of plasma triglyceride (TG) levels by both being a potent stimulator of apo-CII lipoprotein lipase (LPL) TG hydrolysis and an inhibitor of the hepatic VLDL-TG production rate (without affecting the VLDL-apoB production rate). Activates poorly lecithin:cholesterol acyltransferase (LCAT) and does not enhance efflux of cholesterol from macrophages (By similarity). Binds heparin (By similarity). Interacts with GPIHBP1 (By similarity). Interacts with SORL1; this interaction leads to APOA5 internalization and sorting either to lysosomes and degradation, or to the trans-Golgi network (By similarity). In the presence of SORL1, internalized to early endosomes, sorted in a retrograde fashion to late endosomes, from which a portion is sent to lysosomes and degradation, another portion is sorted to the trans-Golgi network. Liver. Induced in early phase of liver regeneration. Phosphorylated by FAM20C in the extracellular medium. Mice expressing the human APOAV transgene show a decrease in plasma TG by one third. Conversely, knockout mice lacking APOAV have a four time increase in plasma TG. Belongs to the apolipoprotein A1/A4/E family.