Comparison of the Four Classification Schemes for the ABC Transporter System
| Transport system | K. Tomii and M. Kanehisa | R. Tam and M. Saier | W. Saurin and E. Dassa | SCOP |
| Sulfate, nitrate, etc. | 1-1, 1-2 | 1, 6 | 1 | II |
| Phosphate | 3-7 | 1 | II | |
| Polar amino acids | 3-3 | 3 | 2 | II |
| Branched-chain amino acids | 3-5 | 4 | 5, 6 | I |
| Peptide | 4-1 | 5 | 3, 4 | II |
| Simple sugar | 2 | 2 | 7 | I |
| Iron complex | 5-1 | 8 | 8 | ? |
| Manganese | 5-2 | |||
| Cobalt | 5-3 | |||
| Multidrug resistance | 6 | |||
| Export (ABC-2) | 7, 11 | |||
| Cell division? | 3-1 |