The Na+-K+-ATPase β1 subunit is associated with the HKα2 protein in the rat kidney

The Na-K-ATPase beta 1 subunit. acts as the beta subunit for the HK alpha(2) protein in the rat kidney. The colonic H+-K+-ATPase is a member of the P-type ATPases, and has been shown to contribute to potassium transport by the mammalian kidney; and colon. The P-type ATPases often consist of an alpha subunit that contains the catalytic site and a beta subunit that participates In regulation of enzyme activity; and targeting of the enzyme to the plasma membrane. The cDNA of the alpha subunit (HK alpha(2)) has been cloned and the HK alpha(2) protein has been isolated from the rat kidney and colon. However, a unique beta subunit for the colonic H+-K+-ATPase has not been described. To determine if one of the known beta subunits present in the kidney might act as the beta subunit for the colonic H+-K+-ATPase, microsomes enriched in the colonic H+-K+-ATPase were isolated using an HK alpha(2)-specific antibody (AS 31.7) and the Minimac magnetic separation system. Immunoblots of rat kidney microsomal protein isolated with antibody AS 31.7 were probed with antibodies directed against the gastric HK beta subunit. Na+-K+-ATPase alpha 1, and Na+-K+-ATPase beta 1 subunits. A band of the appropriate size was detected with Na+-K+-ATPase beta(1)-specific antibodies, but not those directed against HK beta(1). These data suggest that Na+-K+-ATPase beta(1) could be the beta subunit for the colonic H+-K+-ATPase in the kidney.