アイテム詳細

要旨

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.