Characterization of amino acid substitutions in KdpA, the K+-binding and -translocating subunit of the KdpFABC complex of Escherichia coli

When grown under K+ limitation, Escherichia coli induces the K+-translocating KdpFABC complex. The stimulation of ATPase activity by NH4+ ions was shown for the first time. Substitutions in KdpA, which is responsible for K+ binding and translocation, revealed that enzyme complexes KdpA:G232A and KdpA:G232S have completely lost their cation selectivity.