TABLE 6.
Arginine and lysine transport activities of wild-type and mutant Can1 proteins
Uptake assays were carried out in the 22Δ8AA strain grown on minimal medium containing 20 mm NH4+ as the sole nitrogen source. For “activity measurements,” 14C-labeled amino acids were added at 10 μm final concentration, and the values represent the average ± S.D. of 2–3 independent experiments. The Vmax and Km values and corresponding S.D. values were calculated for each mutant from the Michaelis-Menten plots shown in Fig. 6. ND, not determined, when the uptake rate was below the detection threshold.
| Permease | Arginine transport |
Lysine transport |
||||
|---|---|---|---|---|---|---|
| Activity | Vmax | Km | Activity | Vmax | Km | |
| nmol·min−1·mg−1 protein | nmol·min−1·mg−1 protein | μm | nmol·min−1·mg−1 protein | nmol·min−1·mg−1 protein | μm | |
| Can1 | 5.5 ± 0.1 | 10.5 ± 0.4 | 10.3 ± 1.3 | 0.2 ± 0.1 | 4.1 ± 0.5 | 148.7 ± 25.5 |
| Can1S176N | ND | ND | ND | ND | ND | ND |
| Can1S176A | 0.7 ± 0.1 | 11.3 ± 0.5 | 78 ± 6.4 | 0.2 ± 0.1 | 3.9 ± 0.2 | 107.5 ± 9 |
| Can1T456S | 9.2 ± 0.2 | 17 ± 0.7 | 4.9 ± 0.8 | 4.8 ± 0.5 | 13.1 ± 0.3 | 13 ± 1 |
| Can1T456A | 5.8 ± 0.1 | 12.3 ± 0.4 | 3 ± 0.5 | 1.1 ± 0.1 | 4.9 ± 0.4 | 25.7 ± 4.6 |
| Can1S176N/T456S | ND | ND | ND | 1.9 ± 0.1 | 3.6 ± 0.2 | 13.2 ± 1.8 |
| Lyp1 | ND | ND | ND | 2.9 ± 0.2 | 4.5 ± 0.1 | 10.4 ± 0.7 |