Part of the high-affinity ATP-driven potassium transport (or Kdp) system, which catalyzes the hydrolysis of ATP coupled with the electrogenic transport of potassium into the cytoplasm (PubMed:23930894, PubMed:2849541, PubMed:8499455). This subunit is responsible for energy coupling to the transport system and for the release of the potassium ions to the cytoplasm (PubMed:16354672, PubMed:30478378, PubMed:34272288). ATP + H2O + K(+)(out) = ADP + H(+) + K(+)(in) + phosphate ATPase activity is inhibited by phosphorylation at Ser-162 (PubMed:28636601, PubMed:30478378). ATPase activity is inhibited by vanadate, fluorescein isothiocyanate, N,N'-dicyclohexylcarbodiimide and N-ethylmaleimide. The system is composed of three essential subunits: KdpA, KdpB and KdpC (PubMed:2849541, PubMed:9858692, PubMed:28636601, PubMed:30478378). The complex also contains KdpF, a small non-essential subunit (PubMed:10608856, PubMed:28636601, PubMed:30478378). The KdpFABC complex exists as a dimer above concentrations of 30-50 nM, whereas the complex exists as a functional monomer at lower concentrations (PubMed:18298081). Transcriptionally regulated by the KdpD/KdpE two-component regulatory system. A protein-embedded tunnel connects the potassium ion in KdpA to a water molecule at the canonical cation site in the transmembrane domain of KdpB (PubMed:28636601, PubMed:30478378, PubMed:34272288). The structures suggest a translocation pathway for potassium via two inter-subunit half-channels along KdpA and KdpB, integrating KdpB directly in the transport process (PubMed:30478378). The periplasmic potassium ion probably enters the selectivity filter of KdpA, travels through the water-filled tunnel to reach KdpB, and is released to the cytoplasm by KdpB (PubMed:34272288). KdpB undergoes conformational changes, whereas KdpA, KdpC and KdpF remain static (PubMed:34272288). Phosphorylated at Ser-162, which leads to the inhibition of the ATPase activity. Belongs to the cation transport ATPase (P-type) (TC 3.A.3) family. Type IA subfamily.