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 NH(4)(+) 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.