Abstract
| - We have used expression of chimeras between the structurallyrelated Na,K- and H,K-ATPaseα subunits to localize regions that determine Na,K-ATPase activity.Segments of the rat Na,K-ATPaseα1 subunit were replaced by the corresponding portions of the ratgastric H,K-ATPase α subunit, and theconstructs were transfected into ouabain-sensitive human HEK 293 cells.Using the ability to transferouabain resistance as a measure of sodium pump activity, we identifiedsegments within the sodium pumpthat could be replaced with proton pump sequences without the loss ofbiological activity. Thesefunctionally interchangeable segments encompassed approximately 75% ofthe amino acid differencesbetween the two transporters. Segments that could not be exchangedmapped to three discrete regions.One region spans residues 63−117 and includes the firsttransmembrane (TM) segment and a portion ofthe amino-terminal cytoplasmic domain. The second, from residue320 to residue 413, encompasses TM4 and a portion of the third cytoplasmic domain, while the third region(encompassing residues 735−861and 898−953) includes several TM domains in the carboxyl-terminalportion of the ATPase. Our resultssuggest that functional differences between Na,K- and H,K-ATPase,including differences in ion transportspecificity, are likely to reside within these noninterchangeablesegments.
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