Kinetic constants of purine nucleobase uptake in L. majorpromastigotes
| [3H]Adenine | n | [3H]Hypoxanthine | N | [3H]Allopurinol | n | |
|---|---|---|---|---|---|---|
| μM | μM | μM | ||||
| K m | 4.6 ± 0.9 | 3 | 0.71 ± 0.07 | 4 | 54.3 ± 2.9 | 3 |
| V max 1-a | 3.2 ± 0.3 | 3 | 2.8 ± 0.6 | 4 | 0.24 ± 0.06 | 3 |
| K iValues | ||||||
| Adenine | 3.0 ± 0.5 | 3 | ||||
| Hypoxanthine | 1.3 ± 0.3 | 3 | 0.30 ± 0.09 | 3 | ||
| Allopurinol | 56 ± 1.5 | 3 | ||||
| Guanine | 2.8 ± 0.7 | 4 | ||||
| Xanthine | 23 ± 8 | 3 | ||||
| Adenosine | 5150 ± 550 | 3 | ||||
| Inosine | 125 ± 15 | 3 | ||||
| Guanosine | 68 ± 17 | 4 | ||||
| Purine | 6.7 ± 0.4 | 3 | ||||
| 1-Deazapurine | 26 ± 4.1 | 3 | ||||
| 3-Deazaguanine | 48 ± 5 | 3 | ||||
| 6-Thioguanine | 6.2 ± 0.8 | 3 | ||||
| 7-Deazaguanine | 426 ± 140 | 3 | ||||
| 9-Deazaguanine | 204 ± 4 | 3 |
Kinetic parameters were determined through competitive inhibition of the indicated 3H-permeants, as described underMaterials and Methods, with 8 to 11 inhibitor concentrations over the relevant range. In a few cases, extrapolation was required because of limitations of solubility of the inhibitor (see Fig. 1B) and based on the assumption of a Hill slope of −1 and eventual 100% inhibition. Extrapolation was not attempted when inhibition at the highest inhibitor concentration was <50%. Permeant concentration was 0.1 μM (adenine and hypoxanthine) or 0.5 μM (allopurinol).
↵1-a Expressed as pmol/107cells/s.