Table 1.

Numbers of Sco transport proteins according to TC class and subclass

TC class a	Class description	No. of proteins	TC subclass	Subclass description	No. of proteins
1	Channel/Pore	20	1.A	α-type channel	19
			1.B	β-type porin	0
			1.C	Pore-forming toxin	1
2	Secondary carrier	277	2.A	Porter (uniporter, symporter, antiporter)	277
3	Primary active transporter	321	3.A	P-P-bond hydrolysis-driven transporter	286
			3.B	Decarboxylation-driven transporter	4
			3.D	Oxidoreduction-driven transporter	28
			3.E	Light absorption-driven transporter	3
4	Group translocator	7	4.A	Phosphotransfer-driven group translocator	5
			4.B	Nicotinamide ribonucleoside uptake transporter	1
			4.C	Acyl CoA ligase-coupled transporter	1
5	Transmembrane electron carrier	9	5.A	Transmembrane 2-electron transfer carrier	8
			5.B	Transmembrane 1-electron transfer carrier	1
8	Auxiliary transport proteinb	4	8.A	Auxiliary transport protein	4
9	Poorly defined system	20	9.A	Recognized transporter of unknown biochemical mechanism	20
Total		658

Detailed class and subclass descriptions can be found at http://www.tcdb.org.

^a Transporter classes 6 and 7 have not been assigned in the TC system yet and therefore are not listed here.

^b Auxiliary proteins facilitate transport via established transport systems and therefore are not counted as separate systems.