Table 1.
V0.5 and z at 100 and 0 mM [Na+]o
| V0.5, mV |
Z |
|||
| Mutant | 100 Na+ | 0 Na+ | 100 Na+ | 0 Na+ |
| hSGLT1 | −39 ± 2 | < −120 | 1.0 ± 0.1 | n.m. |
| Near sugar binding | ||||
| H83C | −42 ± 3 | −120 to −140 | 0.9 ± 0.1 | n.m. |
| T287C | −47 ± 1 | < −120 | 1.0 ± 0.1 | n.m. |
| Y290C | 3 ± 4 | −54 ± 4 | 0.9 ± 0.1 | 0.6 ± 0.1 |
| Y290S | 18 ± 1 | −40 ± 6 | 0.9 ± 0.1 | 0.7 ± 0.1 |
| Y290F | −49 ± 13 | < −120 | 0.9 ± 0.1 | n.m. |
| W291C | 12 ± 2 | −53 ± 2 | 0.9 ± 0.1 | 0.6 ± 0.1 |
| W291F | −49 ± 9 | < −120 | 1.0 ± 0.1 | n.m. |
| Q457C | −55 ± 4 | < −120 | 1.0 ± 0.1 | n.m |
| Near Na2 site | ||||
| D204E* | −50 ± 2 | −67 ± 3 | ∼1 | ∼1 |
| S392A/C | −56 ± 3 | −100 to −140 | 0.9 ± 0.1 | n.m. |
| Other | ||||
| F101C | −3 ± 3 | < −120 | 1.0 ± 0.1 | n.m. |
| F453C | −28 ± 4 | < −120 | 1.0 ± 0.1 | n.m. |
| G507C | −35 ± 1 | < −120 | 1.0 ± 0.1 | n.m. |
Kinetics are mean ± SE of three to nine oocytes from at least two donor frogs. For mutants with Q/V curves that did not saturate (within the range −150 mV and +50 mV) at 0 Na+, we were unable to obtain reliable estimates of V0.5 and z. V0.5 was more negative than −120 mV (< −120 mV) and z was designated by nonmeasurable (n.m.). At 0 Na+, z = z1, and at 100 mM Na+, z = z1 + z2 + z3 (Eq. 9).
*
Data are from Quick et al. (25), where the data at 0 Na+ were actually obtained in 5 mM Na+.