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+.