Purification and Characterization of a Cation-stimulated Adenosine Triphosphatase from Corn Roots

A membrane-bound, monovalent cation-stimulated ATPase from Zea mays roots has been purified to a single band on sodium dodecyl sulfate gel electrophoresis. Microsomal preparations with K(+) -stimulated ATPase activity were extracted with 1 m NaClO(4), and the solubilized enzyme was purified by chromatography on columns of n-hexyl-Sepharose, DEAE-cellulose, and Sephadex G-100 Superfine. A 500-fold purification over the activity present in the microsomes was obtained. The K(+) -stimulated activity shows positive cooperativity with increasing KCl concentrations. The purified enzyme shows K(+) -stimulated activity with ATP, GTP, UTP, CTP, ADP, alpha + beta-glycerophosphate, p-nitrophenyl phosphate, and pyrophosphate as substrates. Under most conditions ATP is the best substrate. Although dicyclohexyl carbodiimide and Ca(2+) inhibit and alkylguanidines stimulate the K(+) -ATPase while bound to microsomes, they have no effect on the purified enzyme.