Enables antioxidant activity. Involved in several processes, including cholesterol efflux; high-density lipoprotein particle clearance; and plasma lipoprotein particle organization. Acts upstream of or within lipoprotein metabolic process and reverse cholesterol transport. Located in extracellular region. Part of discoidal high-density lipoprotein particle. Is expressed in several structures, including gut; liver; male reproductive gland or organ; and urinary system. Human ortholog(s) of this gene implicated in coronary artery disease; type 1 diabetes mellitus; and type 2 diabetes mellitus. Orthologous to human APOM (apolipoprotein M). [provided by Alliance of Genome Resources, Apr 2022]