Purification of active Na+-K+-ATPase using a new ouabain-affinity column

Ouabain, a specific inhibitor of Na+-K+-ATPase, was coupled to epoxy agarose via a 13-atom spacer to make an affinity column that specifically binds Na+-K+-ATPase. Na+-K+-ATPase from rat and dog kidney was bound to the column and was eluted as a function of enzyme conformation, altered by adding specific combinations of ligands. Na+-K+-ATPase from both sources bound to the column in the presence of Na + ATP + Mg and in solutions containing 30 mM K. No binding was observed in the presence of Na or Na + ATP. These experiments suggest that Na+-K+-ATPase binds to the column under the same conditions that it binds to untethered ouabain. Na+-K+-ATPase already bound to the column was competitively eluted with excess free Na + ouabain or with Na + ATP. The latter eluted active enzyme. For comparable amounts of bound Na+-K+-ATPase, Na + ouabain and Na + ATP eluted more rat than dog Na+-K+-ATPase, consistent with the lower affinity of the rat Na+-K+-ATPase for ouabain. The ouabain-affinity column was used to purify active Na+-K+-ATPase from rat kidney microsomes and rat adrenal glomerulosa cells. The specific activity of the kidney enzyme was increased from approximately 2 to 15 micromol Pi . mg-1 . min-1. Na+-K+-ATPase purified from glomerulosa cells that were prelabeled with [32P]orthophosphate was phosphorylated on the alpha-subunit, suggesting that these cells contain a kinase that phosphorylates Na+-K+-ATPase.