TABLE 4.
Comparison of MTX influx kinetics between mutated and wild-type PCFTs
MTX influx was measured at pH 5.5 over 1 min. Kt and Vmax values are the mean ± S.E. from three independent experiments determined from nonlinear regression to the Michaelis-Menten equation. Due to low MTX influx in the L161R mutant, background uptake in mock transfectants was subtracted from uptake in L161R transfectants. Modified Vmax was obtained by normalizing to the protein levels at the plasma membrane.
|
Kt |
Vmax |
|||||
|---|---|---|---|---|---|---|
| μm | Mutant/wild-type | Unmodified | Relative plasma membrane expression | Modified | Mutant/wild-type | |
| pmol/mg protein/min | pmol/mg protein/min | |||||
| Wild-type | 2.3 ± 0.3 | 361 ± 15 | 1.00 | 361 | ||
| E232G | 0.33 ± 0.03 | 0.15 | 23.1 ± 1.5 | 0.35 | 66 | 0.18 |
| I304F | 9.8 ± 1.3 | 4.3 | 199 ± 44 | 1.02 | 195 | 0.54 |
| L161R | 84 ± 8 | 37 | 73 ± 10 | 0.75 | 97 | 0.27 |