Table 4.

Numbers of Mxa 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	21	1.A	α-type channel	18
			1.B	β-type porin	3
2	Secondary carrier	153	2.A	Porter (uniporter, symporter, antiporter)	153
3	Primary active transporter	146	3.A	P-P-bond hydrolysis-driven transporter	124
			3.B	Decarboxylation-driven transporter	4
			3.D	Oxidoreduction-driven transporter	18
4	Group translocator	7	4.A	Phosphotransfer-driven group translocator	2
			4.C	Acyl CoA ligase-coupled transporter	5
5	Transmembrane electron carrier	10	5.A	Transmembrane 2-electron transfer carrier	10
8	Auxiliary transport proteinb	8	8.A	Auxiliary transport protein	8
9	Poorly defined system	10	9.A	Recognized transporter of unknown biochemical mechanism	10
Total		355			355

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 a separate system.