Table 1.
Functional parameters of Y780 mutants
| Turnover rate | K0.5, Na+ phosphorylation | K0.5, K+ ATPase activity | K0.5,K+ inhibition of phosphorylation | E2P fraction/dephosphorylation rate in Na+ | K0.5,K+ IP in NMDG+ | K0.5,K+ IP in Na+ | V1/2 | |
|---|---|---|---|---|---|---|---|---|
| s−1 | mM | mM | μM | %/s−1 | mM | mM | mV | |
| WT | 138 ± 16 (16) | 0.50 ± 0.08 (17) | 0.57 ± 0.09 (14) | 96 ± 12 (3) | 41 ± 8 (8) 0.14 ± 0.02 |
0.22 ± 0.09 (6) | 1.3 ± 0.1 (3) | −51 ± 8 (8) |
| Y780A | 61 ± 9 (12) | 24.0 ± 3.3 (6) 48-fold ↑ |
1.8 ± 0.6 (8) 3.2-fold ↑ |
376 ± 118 (3) 3.9-fold ↑ |
37 ± 9 (3) 0.07 ± 0.03 |
1.9 ± 0.7 (4) 8.6-fold ↑ |
2.5 ± 0.8 (4) 1.9-fold ↑ |
−180* (6) 36–87-fold↑ |
| Y780L | 137 ± 43 (16) | 6.0 ± 0.6 (2) 12-fold ↑ |
0.63 ± 0.11 (6) 1.1-fold ↑ |
126 ± 37 (4) 1.3-fold ↑ |
48 ± 5 (2) 0.11 ± 0.002 |
0.53 ± 0.06 (4) 2.4-fold ↑ |
1.5 ± 0.1 (5) 1.2-fold ↑ |
ND |
| Y780F | 148 ± 12 (6) | 8.1 ± 2.0 (6) 16-fold ↑ |
0.78 ± 0.13 (3) 1.4-fold ↑ |
159 ± 56 (3) 1.7-fold ↑ |
42 ± 20 (4) 0.22 ± 0.01 |
1.4 ± 0.5 (8) 6.4-fold ↑ |
2.0 ± 0.7 (4) 1.5-fold ↑ |
−137 ± 13 (12) 11–20 fold↑ |
| Y780Q | 81 ± 8 (6) | 0.25 ± 0.05 (9) 2-fold ↓ |
2.5 ± 0.3 (5) 4.4-fold ↑ |
422 ± 41 (3) 4.4-fold ↑ |
45 ± 10 (3) 0.04 ± 0.02 |
2.0 ± 0.7 (18) 9.1-fold ↑ |
10.3 ± 0.3 (3) 7.7-fold ↑ |
−33 ± 13 (6) 1.7–1.9-fold ↓ |
The data were extracted from results in Figs. 3, 4, 5, 6, and 7, except the turnover rates of Y780A/L/Q, which were obtained as described in Fig. 4 E. The K+-inhibition of phosphorylation of Y780F was carried out as described for WT and the other mutants in the legend to Fig. 6 C. Average values are indicated with SD and number of determinations in parentheses, except in the case marked by *, where fit to average data was applied. Range of fold changes in K0.5 for external Na+ given a shift in V1/2 was obtained, based on 25 mV/twofold change and ∼20 mV/twofold change (based on results from Holmgren and Rakowski, 1994; Holmgren and Rakowski, 2006; Vedovato and Gadsby, 2010, and consistent with our data in Fig. 3 F).