PRIMARY STRUCTURE AND FUNCTIONAL EXPRESSION OF THE MOUSE AND FROG ALPHA-SUBUNIT OF THE GASTRIC H-K+-ATPASE()

The H+-K+-ATPase of the gastric parietal cells is responsible for the acidification of the stomach lumen. This heterodimeric protein belongs to the family of cation-translocating P-type ATPases, which includes the closely related Na+-K+-ATPase. We have cloned the alpha-subunit cD NA of the Xenopus and murine gastric H+-K+-ATPase (alpha(H-K)). We hav e expressed Xenopus and murine alpha(H-K) along with the previously cl oned gastric H+-K+-ATPase beta-subunit of rabbit (beta(H-K)) in Xenopu s oocytes by cRNA injection. An antibody directed against the beta(H-K ) coimmunoprecipitates under nondenaturing conditions the alpha(H-K) O f both species, demonstrating assembly of the alpha/beta complex. Addi tionally, we demonstrate the presence of K+-transporting H+-K+-ATPase in the plasma membrane of oocytes by Rb-86(+) uptake. The H+-K+-ATPase -mediated K+ uptake was inhibited by the gastric H+-K+-ATPase inhibito r Sch-28080, but not by ouabain, and shows K+-dependent activation (K- 1/2 similar to 2 mM). Furthermore, H+-K+-ATPase-expressing oocytes sho w a Sch-28080 inhibitable proton extrusion. Our data indicate that the expressed H+-K+-ATPase behaves functionally in oocytes as in the gast ric gland.