Table I.
Comparison of the affinities of all three AtProTs for Pro, Gly betaine, and GABA
The uptake of radiolabeled substrates was determined in 22574d cells expressing AtProT1, AtProT2, or AtProT3. The pH of the assay medium was 4.5. Uptake rates were determined at five different substrate concentrations and the apparent affinities and maximal transport rates were determined. Values represent the mean of at least three experiments ± sd.
| Transporter
|
Pro
|
Gly Betaine
|
GABA
|
|||
|---|---|---|---|---|---|---|
| Km | Vmax | Km | Vmax | Km | Vmax | |
| mm | nmol × 10−8 cells × min−1 | mm | nmol × 10−8 cells × min−1 | mm | nmol × 10−8 cells × min−1 | |
| AtProT1 | 0.427 ± 0.017 | 29 ± 1.0 | 0.115 ± 0.009 | 11 ± 0.1 | 4.50 ± 0.26 | 41 ± 4.6 |
| AtProT2 | 0.500 ± 0.005 | 42 ± 1.4 | 0.267 ± 0.018 | 17 ± 0.4 | 4.01 ± 0.64 | 60 ± 4.5 |
| AtProT3 | 0.999 ± 0.036 | 19 ± 2.1 | 0.290 ± 0.027 | 3.6 ± 0.6 | 5.12 ± 0.12 | 34 ± 1.8 |