Functional expression of N-terminal truncated α-subunits of Na,K-ATPase in Xenopus laevis oocytes

N-terminal deletion mutants of Na,K-ATPase α₁ isoforms initiating translation at Met³⁴ (α₁T₁) or at Met⁴³ (α₁T₂) were expressed in X. laevis oocytes. Compared to β₃ cRNA injected controls, the co-expression of α₁wt, α₁T₁, α₁T₂ with β₃ subunits results in a 2- to 3-fold increase of ouabain binding sites, parallelled by a concomitant increase in Na,K-pump current. The apparent K for potassium activation of the α₁T₂/β₃ Na,K-pumps is significantly higher than that of the α₁wt/β₃ or α₁T₁/β₃ Na,K-pumps expressed at the cell surface. Total deletion of the lysine-rich N-terminal domain thus allows the expression of active Na,K-pump but with distinct cation transport properties.