The solute carrier (SLC) group of membrane transport proteins include over 400 members organized into 66 families. Most members of the SLC group are located in the cell membranem. SLCs contain a number of hydrophobic transmembrane alpha helices connected to each other by hydrophilic intra- and extra-cellular loops. Depending on the SLC, these transporters are functional as either monomers or obligate homo- or hetero-oligomers. Many SLC families are members of the major facilitator superfamily.