THE C-TERMINAL 165-AMINO-ACIDS OF THE PLASMA-MEMBRANE CA2-ATPASE CONFER CA2+()CALMODULIN SENSITIVITY ON THE NA+,K+-ATPASE ALPHA-SUBUNIT/

The C-terminal 165 amino acids of the rat brain plasma membrane (PM) C a2+-ATPase II containing the calmodulin binding auto-inhibitory domain was connected to the C-terminus of the ouabain sensitive chicken Na+, K+-ATPase alpha 1 subunit. Expression of this chimeric molecule in oua bain resistant mouse L cells was assured by the high-affinity binding of [H-3]ouabain. In the presence of Ca2+/calmodulin, this chimeric mol ecule exhibited ouabain inhibitable Na+,K+-ATPase activity; the putati ve chimeric ATPase activity was absent in the absence of Ca2+/calmodul in and activated by Ca2+/calmodulin in a dose-dependent manner. Furthe rmore, this chimeric molecule could bind monoclonal IgG 5 specific to the chicken Na+,K+-ATPase alpha 1 subunit only in the presence of Ca2/calmodulin, suggesting that the epitope for IgG 5 in this chimera is masked in the absence of Ca2+/calmodulin and uncovered in their presen ce. These results propose a direct interaction between the calmodulin binding auto-inhibitory domain of the PM Ca2+-ATPase and the specific regions of the Na+,K+-ATPase alpha 1 subunit that are structurally hom ologous to the PM Ca2+-ATPase. A comparison of the deduced amino acid sequences revealed several possible regions within the Na+,K+-ATPase t hat might interact with the auto-inhibitory domain of the PM Ca2+-ATPa se.