Table 2.
Effect of inhibitors on the reconstituted ascorbic acid unidirectional uptake.
| Inhibitor | (mM) | Inhibition (%) | |
|---|---|---|---|
| Rat | Potato | ||
| N-Ethylmaleimide | 2.0 | 0 | 0 |
| HgCl2 | 0.5 | 0 | 0 |
| 4,4′-Diisothiocyano-2,2′-stilbenedisulfonic acid (DIDS) | 5.0 | 0 | 0 |
| Glucose | 20 | 0 | 0 |
| Mannitol | 20 | 0 | 0 |
| Cytochalasin B | 0.5 | 0 | 0 |
| Galactosamine | 20 | 0 | 0 |
| p-Hydroxymercuribenzoate | 1.0 | 40 ± 7.5 | 38 ± 8.0 |
| Phenylmaleimide | 1.0 | 43 ± 8.5 | 46 ± 8.3 |
| Bathophenanthroline | 20 | 45 ± 3.5 | 44 ± 11 |
| Pyridoxal 5′-phosphate (PLP) | 15 | 80 ± 4.0 | 75 ± 5.3 |
The uptake was started by adding 0.1 mM external [14C]ascorbic acid to proteoliposomes reconstituted with HTP eluate, from rat liver and from potato, in the absence of internal substrate. The inhibitors were added together with the labeled substrate. The control value of uninhibited ascorbic acid uptake was 1.13 nmol × mg protein−1 × 10 min−1 and 0.28 nmol × mg protein−1 × 10 min−1 protein respectively for rat and potato.