Transporters of unknown classification. Transport protein families of unknown classification are grouped under TC category 9. Permeases within families maintained in the 9A class are of unknown mode of transport or energy-coupling mechanism, but at least one member of each of these families has clearly been shown to function as a transporter. These families will be classified elsewhere when the transport process and energy-coupling mechanism are characterized. Putative transport protein families are grouped under TC number 9B if they are putative transporters in which no family member is an established transporter. The family will either be classified elsewhere when the transport function of a member becomes established or will be eliminated from the TC classification system if the proposed transport function is disproven. These families include a member or members for which a transport function has been suggested, but evidence for such a function is not yet compelling. Functionally characterized transporters for which sequences and/or family association are not available are grouped in class 9C.

These include:

9.A Transporters of unknown biochemical mechanism. Transport protein families of unknown classification are grouped in this subclass and will be classified elsewhere when the transport mode and/or energy coupling mechanism are characterized. These families include at least one member for which a transport function has been established, but either the mode of transport or the energy coupling mechanism is not known.

9.B Putative uncharacterized transport proteins. Putative transport protein families are grouped in this subclass and will either be classified elsewhere when the transport function of a member becomes established, or will be eliminated from the TC classification system if the proposed transport function is disproven. These families include a member or members for which a transport function has been suggested, but evidence for such a function is not yet compelling.

9.C Functionally characterized transport proteins with unidentified sequences. Transporters of particular physiological significance will be included in this category even though a family assignment cannot be made. When their sequences are identified, they will be assigned to an established family. This is the only protein subclass which includes individual proteins rather than protein families.