抄録
To investigate which regions of the Na, K-ATPase β subunit are required for the functional αβ complex formation of the Na, K-ATPase, we constructed chimeric β subunits between the Na, K-and the H, K-ATPase β subunits, and expressed in Xenopus oocytes together with the Na, K-ATPase α subunit. The chimera, that was composed of N-terminal cytoplasmic region of the H, K-ATPase β subunit combined with transmembrane and extracellular region of the Na, K-ATPase β subunit, formed a functional enzyme with the Na, K-ATPase α subunit. This means that N-terminal cytoplasmic region of the β subunit is interchangeable between the Na, K-and H, K-ATPases. The chimeras, whose C-terminal extracellular domain was derived from H, K-ATPase β subunit, formed inactive enzyme in ATPase activity, suggesting that the extracellular domain was essential for the functional expression of the Na, K-ATPase.
The Cys127-Cysl50 disulfide-bonded loop (L1) located within the extracellular domain of the Na, K-ATPase β subunit was substituted with the corresponding loop of pig H, K-ATPase β subunit. The complex of the α subunit with this mutant β subunit was inactive in ATP hydrolysis. Phe148 within the L1 of the pig H, K-ATPase β subunit-substituted mutant were back-mutated to Arg148. This mutation restored the ability of the mutant β subunit to form a functional complex with the α subunit. These results suggested that the Cys127-Cys150 loop of the Na, K-ATPase β subunit, especially Arg148, plays a critical role in the functional expression of the Na, K-ATPase.
