HUMAN ATP1AL1 GENE ENCODES A OUABAIN-SENSITIVE H-K-ATPASE

The cDNA for ATP1AL1, the fifth member of the human Na-K-adenosinetriphosphatase (ATPase)/H-K-ATPase gene family, was recently cloned (A. V. Griskin, V. E. Sverdlov, M. B. Kostina, and N. N. Modyanov. FEES Lett. 349: 144-150, 1994). The encoded protein (ATP1AL1) has all the primary structural features common to the catalytic alpha-subunit of ion-transporting P-type ATPases and is similar (63-64% identity) to the Na-K-ATPase alpha-subunit isoforms and the gastric H-K-ATPase alpha-subunit. In this study, ATP1AL1 was expressed in Xenopus laevis oocytes in combination with the beta-subunit of rabbit gastric H-K-ATPase. The functional properties of the stable alpha/beta-complex were studied by Rb-86(+) uptake and demonstrated that ATP1AL1 is a novel human K+-dependent ATPase [apparent half-constant activation/(K-1/2) for K+ similar to 375 mu M)]. ATP1AL1-mediated inward K+ transport was inhibited by ouabain (inhibition constant similar to 13 mu M) and was found to be inhibited by high concentrations of SCH-28080 (similar to 70% at 500 mu M)]. ATP1AL1 expression resulted in the alkalinization of the oocytes' cytoplasm and. ouabain-sensitive proton extrusion, as measured with pH-sensitive microelectrodes. These data argue that ATP1AL1 is the catalytic alpha-subunit of a human nongastric P-type ATPase capable of exchanging extracellular potassium for intracellular protons.