Table 7.
Competitive uptake of radiolabelled choline, betaine and carnitine in the E. coli transporter-deficient mutant MKH13 expressing selected transporter components.a
| Plasmid 1 | Plasmid 2 | SBP(s) | [14C] Substrate | % inhibition of uptake of substrate with the following unlabelled competitorsa
|
|||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| W | MM | DM | Bet | Cho | Car | AC | PC | ||||
| pNcbcWV | pT-PA3236 | BetX | Betaine | 0 | −13 | 56 | 94 | −8 | 3 | NT | NT |
| pNcbcWV | pT-PA5388 | CaiX | Car | 0 | 0 | 2 | 5 | 5 | 91 | NT | NT |
| pNcbcXWV | pT-PA5388 | CaiX/CbcX | Car | 0 | −1 | 7 | 57 | 66 | 97 | NT | NT |
| pNcbcXWV | None | CbcX | Betaine | 0 | −3 | −5 | 87 | 99 | 3 | NT | NT |
| pNcbcXWV | pT-PA5388 | CbcX/CaiX | Betaine | 0 | 3 | −4 | 88 | 99 | 10 | NT | NT |
| pNcbcXWV | None | CbcX | Choline | 0 | 2 | 4 | 2 | 92 | 6 | 9 | 1 |
| pNcbcXWV | pT-PA5388 | CbcX/CaiX | Choline | 0 | 2 | −8 | −1 | 96 | −2 | NT | NT |
| pNchoXWV | None | ChoX | Choline | 0 | −4 | −6 | 3 | 98 | 41 | 88 | 5 |
a
Uptake was evaluated using radiolabelled substrates (10 μM) in the presence of unlabelled competitors (1 mM). The steady-state total uptake in absence of competitors (Water) were, by row, 8.6, 14, 11, 9.8, 11.8, 17.7, 29.5 and 16.7 nmol (mg protein)−1. W, water; MM, monomethylglycine; DM, dimethylglycine; Bet, glycine betaine; Cho, choline; Car, carnitine; AC, acetylcholine; PC, phosphorylcholine; NT, not tested. Values are the mean percentage inhibition (n = 3–4), and the results are representative of two independent experiments.