Kinetic parameters of [3H]adenosine transport and guanosine inhibition of [3H]adenosine transport by wild-type and mutant hENT1
The kinetic parameters (Km and Vmax) and guanosine inhibition (Ki) of [3H]adenosine transport by wild-type (WT), single, and Met89Cys/Ser160Cys (cysteine/cysteine) double mutant hENT1-expressing yeast were determined by conducting [3H]adenosine transport in the presence of various concentrations of unlabeled adenosine (0-2 mM) or guanosine (0-3 mM). All values represent the mean ± S.D. (n = 3) of the nonlinear regression parameter estimates.
| Adenosine | Guanosine | ||||
|---|---|---|---|---|---|
| Km | Fold Change from WT | Vmax | Ki | Fold Change from WT | |
| μM | fmol/106 cells/min | μM | |||
| WT | 20.6 ± 4.4 | 1 | 214 ± 85.8 | 178 ± 80 | 1 |
| Met89Cys | 162 ± 60.9* | 7.9 | 726 ± 110* | 1020 ± 110* | 5.7 |
| Ser160Cys | 56.0 ± 19.3* | 2.7 | 394 ± 80.6 | 313 ± 16.7* | 1.8 |
| Cys/Cys | 160 ± 53.6* | 7.8 | 397 ± 168 | 1370 ± 314* | 7.7 |
↵* , significantly different from wild-type transporter (p < 0.05).