The high‐affinity K+‐translocating ATPase complex from Bacillus acidocaldarius consists of three subunits

Summary Cells of the thermoacidophilic bacterium Bacillus acidocaldarius express a high-affinity K+-uptake system when grown at low external K+. A vanadate-sensitive, K+ - and Mg2+ -stimulated ATPase was partially purified from membranes of these cells by solubilization with a non-ionic detergent followed by ion-exchange chromatography of the extract. Combinations of non-denaturing and denaturing electrophoretic separation methods revealed that the ATPase complex consisted of three subunits with molecular weights almost identical to those of the KdpA, B and C proteins, which together form the Kdp high-affinity, K+ -translocating ATPase complex of Escherichia coli. The affinity of the partially purified ATPase from B. acidocaldarius for its substrates K+ (Km 2–3 μM) and ATP (Km 80 μM), its stimulation by various divalent cations, and its inhibition by vanadate (Ki 1–2 μM), bafilomycin A1 (Ki, 20 μM), DCCD (Ki 200 μM) or Ca2+ were also similar to those of the E coli enzyme, indicating that the two K+ -translocating ATPases have almost identical properties.