FIGURE 4.

Conformational E₁P/E₂P distribution and pump currents of β-N-terminally truncated Na,K-ATPase. A, partial amino acid sequences of the N-terminally deleted Na,K-ATPase β-variant NaKβ₁Δ8 and the wild type sheep Na,K-ATPase β₁-subunit (in black). For comparison, the wild type and N-terminally truncated β-variants of the rat H,K-ATPase are also shown (in gray). B, voltage-dependent distribution of fluorescence amplitudes 1 − ΔF/F for Na,K-ATPase complexes consisting of the sheep wild type α₁-subunit and either the unmodified reporter construct β₁S62C (■) or the N-terminally deleted Na,K β-variant β₁S62CΔ8 (○). The same voltage protocol as in Fig. 2 (B–D) was applied in 100 mm Na⁺/K⁺-free solution at pH 7.4. The data are the means ± S.D. of 10–15 oocytes, normalized to saturating values at −180 mV after subtracting the values for −60 mV. A curve corresponding to the fit of a Boltzmann function is superimposed, and the resulting fit parameters V_0.5 and z_q are listed in Table 3. Inset, stationary pump currents of the two constructs at saturating K⁺ concentrations (10 mm). The data are the means ± S.D. of 10–15 oocytes.