Ouabain- and Ca2(+)-sensitive ATPase activity of chimeric Na- and Ca-pump molecules.

Chimeric ion-pumps, consisting of the N-terminal 2/3 of the alpha 1-subunit of the ouabain-sensitive chicken Na+,K(+)-ATPase and the C-terminal 1/3 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 2/3 of the Na-pump, and the C-terminal 1/3 of the Ca-pump interacts with Ca2+.