Functional and Phylogenetic Classification of Membrane Transport ProteinsThe database details a comprehensive IUBMB approved classification system for membrane transport proteins known as the Transporter Classification (TC) system. The TC system is analogous to the Enzyme Commission (EC) system for classification of enzymes, except that it incorporates both functional and phylogenetic information. Descriptions, TC numbers, and examples of 1502 families of transport proteins are provided. Transport systems are classified on the basis of five criteria, and each of these criteria corresponds to one of the five numbers or letters within the TC# for a particular type of transporter.
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Some facts about TCDB:
-  Saier MH, Reddy VS, Tsu BV, Ahmed MS, Li C, Moreno-Hagelsieb G (2016) The Transporter Classification Database (TCDB):
recent advances. Nucleic Acids Res 44, D372–9 
-  Saier MH, Reddy VS, Tamang DG, Vastermark A. (2014), The transporter classification database.
Nucl. Acids Res., 42(1):D251-8 
-  Saier MH Jr, Yen MR, Noto K, Tamang DG, Elkan C. (2009), The Transporter Classification Database: recent advances,
Nucl. Acids Res., 37: D274-8. 
-  Saier MH Jr, Tran CV, Barabote RD. (2006), TCDB: the Transporter Classification Database for membrane transport protein
analyses and information, Nucl. Acids Res., 34: D181-6. 
- [ + references included in TCDB ]