TABLE 1.
Functional properties of purified Na,K-ATPase complexes
Specific activity, K0.5Na+, K0.5K+, and Ki vanadate of purified Na,K-ATPase complexes are shown. Values represent averages of at least three different experiments ± S.E. The reaction medium contained sodium plus potassium as indicated, 1 mm ATP, 3 mm MgCl2, 25 mm histidine, pH 7.4, 1 mm EGTA, 0.01 mg/ml SOPS, 0.001 mg/ml cholesterol, and 0.005 mg/ml C12E8. Maximal Na,K-ATPase activity was measured in the presence of 120 mm NaCl, 20 mm KCl. For ion titrations, ATPase activity was measured in medium containing 80 mm KCl and 0–120 mm NaCl or 120 mm NaCl and 0–40 mm KCl. Ionic strength was maintained constant with choline chloride. K0.5 values were obtained from least square fits of the data points to the Hill equation. Ki vanadate was determined in medium containing 120 mm NaCl, 20 mm KCl, and 1 mm ATP, and data points were fitted to a one-side inhibition model.
| Isoform complexes | Specific Na,K-ATPase activity | K0.5Na+ (nH) | K0.5K+ (nH) | Vanadate Ki |
|---|---|---|---|---|
| μmol/mg/min | mm | mm | μm | |
| α1β1 | 16.4 ± 0.7 | 16 ± 0.4 (1.7 ± 0.1) | 1.5 ± 0.1 (1.8 ± 0.1) | 0.5 ± 0.1 |
| α2β1 | 10.9 ± 0.6 | 17.7 ± 0.5 (1.9 ± 0.2) | 2.7 ± 0.1 (2.0 ± 0.2) | 3.5 ± 0.3 |
| α2β2 | 8.4 ± 1.4 | 9.8 ± 0.7 (1.8 ± 0.2) | 7.4 ± 0.2 (1.7 ± 0.1) | 34.0 ± 2.0 |
| α2β3 | 10.7 ± 1.9 | 13.0 ± 0.2 (1.9 ± 0.2) | 6.4 ± 0.5 (1.8 ± 0.2) | 19.0 ± 1.5 |