THE NA-K+-ATPASE BETA-1 SUBUNIT IS ASSOCIATED WITH THE HK-ALPHA-2 PROTEIN IN THE RAT-KIDNEY()

The Na-K-ATPase beta 1 subunit. acts as the beta subunit for the HK al pha(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 be ta subunit that participates In regulation of enzyme activity; and tar geting of the enzyme to the plasma membrane. The cDNA of the alpha sub unit (HK alpha(2)) has been cloned and the HK alpha(2) protein has bee n isolated from the rat kidney and colon. However, a unique beta subun it for the colonic H+-K+-ATPase has not been described. To determine i f one of the known beta subunits present in the kidney might act as th e beta subunit for the colonic H+-K+-ATPase, microsomes enriched in th e colonic H+-K+-ATPase were isolated using an HK alpha(2)-specific ant ibody (AS 31.7) and the Minimac magnetic separation system. Immunoblot s 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 th e appropriate size was detected with Na+-K+-ATPase beta(1)-specific an tibodies, but not those directed against HK beta(1). These data sugges t that Na+-K+-ATPase beta(1) could be the beta subunit for the colonic H+-K+-ATPase in the kidney.