APOD occurs in the macromolecular complex with lecithin-transport and binding of bilin. Appears to be able to transport a variety of ligands in a number of different contexts. Homodimer. Highest levels of expression in brain, testis, virgin mammary gland and salivary gland. Moderate levels in skeletal muscle, lactating mammary gland and thymus. Low levels in lung and lymph node. No expression in kidney, pancreas, liver or spleen. Belongs to the calycin superfamily. Lipocalin family.