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Abstract:
Chimeric ATPases formed from the α 1 subunit of chicken Na+/K+‐ATPase with COOH‐terminal 165 amino acids of plasma membrane Ca2+‐ATPase‐II of rat brain (NNN‐CBS) were expressed in Xenopus oocytes together with the β subunit of the Na+ pump of Torpedo electroplax; the COOH‐terminal region includes the calmodulin binding site. It was demonstrated previously that this chimera shows Na+,K+‐ dependent ATPase activity but only in the presence of Ca2+/calmodulin, and this activity is inhibited by ouabain. This was taken as additional evidence that the COOH terminus with the calmodulin binding site interacts with regions that are conserved in the Ca2+‐ and Na+,K+‐ATPases; the interaction blocks ATPase activity and is released by Ca2+/calmodulin. To further characterize function of the chimera we measured (3H)ouabain binding to determine the number of pump molecules in the plasma membrane and measured pump‐mediated 86Rb uptake, 22Na efflux, and current. All determinations of transport activity were performed under conditions of maximized turnover.
