Table 1.

Classes and subclasses of transporters in the TC systema

1.  Channels and pores
 1.A  α-Type channels
 1.B  β-Barrel porins
 1.C  Pore-forming toxins (proteins and peptides)
 1.D  Non-ribosomally synthesized channels
2.  Electrochemical potential-driven transporters
 2.A  Porters (uniporters, symporters, and antiporters)
 2.B  Nonribosomally synthesized porters
 2.C  Ion gradient-driven energizers
3.  Primary active transporters
 3.A  Diphosphate bond hydrolysis-driven transporters
 3.B  Decarboxylation-driven transporters
 3.C  Methyl transfer-driven transporters
 3.D  Oxidoreduction-driven transporters
 3.E  Light absorption-driven transporters
4.  Group translocators
 4.A  Phosphotransfer-driven group translocators
8.  Accessory factors involved in transport
 8.A  Auxiliary transport proteins
9.  Incompletely characterized transport systems
 9.A  Recognized transporters of unknown biochemical mechanism
 9.B  Putative but uncharacterized transport proteins
 9.C  Functionally characterized transporters lacking identified sequences
  • a This system of classification was approved by the transporter nomenclature panel of the International Union of Biochemistry and Molecular Biology in Geneva, 28–30 November 1999. No assignment has been made for categories 5 to 7. These will be reserved for novel types of transporters, yet to be discovered, that do not fall within categories 1 to 4.