Plays a role in lipoprotein-mediated cholesterol uptake in hepatocytes (By similarity). Binds cholesterol (PubMed:25732850). Binds free fatty acids and their coenzyme A derivatives, bilirubin, and some other small molecules in the cytoplasm. May be involved in intracellular lipid transport (By similarity). Forms a beta-barrel structure that accommodates hydrophobic ligands in its interior. Deamidation and transpeptidation at the beta carboxyl of Asn-105 forms an isoaspartyl residue found in an isoform of the DE-III fraction. This rearrangement gives rise to an extra negative charge carried by the acid form. There are three fractions of Z-protein: DE-I, DE-II and DE-III. DE-I is virtually lipid free, DE-II binds palmitic, stearic, oleic, linoleic and arachidonic acids and DE-III binds mainly arachidonic acid. Belongs to the calycin superfamily. Fatty-acid binding protein (FABP) family.