A molecule of glycocholate, glycochenodeoxycholate, taurocholate, or taurochenodeoxycholate is transported from the cytosol to the extracellular space, coupled to the hydrolysis of a molecule of cytosolic ATP to ADP and orthophosphate. This reaction is mediated by ABCB11 (bile salt export pump). In the body, this reaction mediates the release of bile salts from the liver cells into the bile (Kullak-Ublick et al. 2004); the role of ABCB11 in the reaction is confirmed by the observed failure of bile salt export in patients in whom the transporter is defective (Noe et al. 2005).