TABLE 1.
Relative Transport of L-Amino Acids versus D-Amino Acids via ATB0,+
| ATB0,+-specific [3H]glycine uptake in HRPE cells (% control) |
ATB0,+-specific inward current in X. laevis oocytes (nA) |
|||
|---|---|---|---|---|
| Amino acid | L-isomer | D-isomer | L-isomer | D-isomer |
| Control | 100 ± 6 | 100 ± 6 | ||
| Alanine | 6 ± 1 | 10 ± 1 | 650 ± 86 | 402 ± 39 |
| Serine | 10 ± 1 | 14 ± 1 | 470 ± 42 | 267 ± 23 |
| Methionine | 3 ± 0 | 14 ± 1 | 278 ± 26 | 213 ± 15 |
| Leucine | 3 ± 1 | 13 ± 1 | 187 ± 14 | 161 ± 25 |
| Tryptophan | 4 ± 1 | 7 ± 1 | 112 ± 4 | 157 ± 23 |
| Threonine | 19 ± 2 | 47 ± 3 | 233 ± 12 | 41 ± 5 |
| Histidine | 9 ± 1 | 35 ± 2 | 410 ± 64 | 29 ± 6 |
| Phenylalanine | 3 ± 0 | 26 ± 2 | 275 ± 58 | 24 ± 24 |
| Glutamine | 13 ± 1 | 77 ± 4 | 453 ± 53 | 16 ± 11 |
| Asparagine | 15 ± 1 | 95 ± 7 | 394 ± 67 | 3 ± 2 |
| Lysine | 18 ± 1 | 86 ± 5 | 321 ± 34 | 9 ± 9 |
| Arginine | 25 ± 1 | 93 ± 6 | 339 ± 35 | 6 ± 1 |
| Valine | 7 ± 1 | 87 ± 4 | 310 ± 24 | 4 ± 3 |
| Isoleucine | 4 ± 1 | 85 ± 5 | 117 ± 16 | 4 ± 4 |
Note. Human retinal pigment epithelial (HRPE) cells were transfected with either vector alone or mouse ATB0,+ cDNA and the functional expression was carried out by the vaccinia virus technique. Transport of [3H]glycine (10 μM) was measured in the presence and absence of various amino acids (2.5 mM). Data represent only cDNA-specific transport. Mouse ATB0,+ was also expressed in Xenopus laevis oocytes and amino acid (1 mM)-induced currents were monitored using the two-microelectrode voltage-clamp technique.