K(+)/H(+) antiporter that extrudes potassium in exchange for external protons and maintains the internal concentration of potassium under toxic levels (PubMed:20163190). In vitro, can also catalyze Rb(+)/H(+), Na(+)/H(+) and, possibly, Li(+)/K(+) exchange, but not Li(+)/H(+) exchange. Nonelectrogenic antiporter that exchanges one cation per proton (PubMed:20163190). H(+)(out) + K(+)(in) = H(+)(in) + K(+)(out) Optimum pH is 7.75. Inactive below pH 6.5. Belongs to the monovalent cation:proton antiporter 1 (CPA1) transporter (TC 2.A.36) family. NhaP2 subfamily.