Ouabain‐ and Ca²⁺‐sensitive ATPase activity of chimeric Na‐ and Ca‐pump molecules

Chimeric ion-pumps, consisting of the N-terminal of the α₁-subunit of the ouabain-sensitive chicken Na⁺, K⁺-ATPase and the C-terminal of the sarcoplasmic reticulum Ca²⁺-ATPase, were expressed in ouabain-insensitive mouse L cells. These chimeric molecules exhibited ouabain-sensitive ATPase activity very similar to that of the wild-type chicken Na⁺ K⁺-ATPase. This ATPase activity could be stimulated by adding Ca²⁺ to the assay system. These results suggest that the sites for ouabain-inhibition are restricted to the N-terminal of the Na-pump, and the C-terminal of the Ca-pump interacts with Ca³⁺.