Apolipoproteins are protein components of plasma lipoproteins. ApoM (Apolipoprotein M), also known as protein G3a, is a member of the Lipocalin family of proteins. ApoM is exclusively expressed in kidney tubular epithelial cells and liver hepatocytes. Mature ApoM retains its signal peptide, which acts as a hydrophobic anchor, and contains a structurally conserved eight stranded antiparallel ∫ barrel which binds retinol and retinoic acid. ApoM may play a key role in reverse cholesterol trans