TABLE 2.

Stabilizing effects of FXYD1 on α1β1, α2β1, α2VFPβ1, and α2Fβ1

K_0.5 FXYD1 was obtained by fitting rates of ATP hydrolysis at different (FXYD1/Na,K-ATPase) ratios to the function v = ((V_max·X)/(X + K_0.5)) + V(−FXYD1). X is (FXYD1/Na,K-ATPase) and V(−FXYD1) is the rate in the absence of FXYD1. The degree of protection is calculated as the ratio V_max/V(−FXYD1) ±S.E. S.E. was calculated as √((V_max/V(−FXYD1)·S.E._v0)² + S.E._Vmax²)/V(−FXYD1). The data represent the average ±S.E. of three or four separate experiments.

	α1β1	α2β1	α2VFPβ1	α2Fβ1
K0.5 FXYD1 ± S.E.	4.2 ± 0.34	6.5 ± 0.78	3.5 ± 1	7.8 ± 0.74
(molar ratio FXYD1/αβ)	n = 4	n = 4 (pα2:α1 = 0.035)	n = 3	n = 3 (pα2:α1 = 0.005)
Vmax/V(−FXYD1) ± S.E.	4.05 ± 0.26	8.81 ± 1.47 (pα2:α1 = 0.02)	5.03 ± 0.07	1.79 ± 0.53 (pα2:α1 = 0.009)