ATP Binding Cassette transporters comprise a large family of membrane-spanning proteins that are responsible for transporting a variety of substrates in prokaryotes and eukaryotes. The most intriguing and, arguably, the most important membrane proteins for this purpose are the ABC (ATP-Binding Cassette) transporters. These proteins, found in all species, use the energy of ATP hydrolysis to translocate specific substrates across cellular membranes. Many of these transporters are responsible for the translocation of lipophilic sub...