TABLE 2.

Cation-dependent ATPase activities of purified KdpFABC complexes^a

Complex	Basal ATPase activityb	Severalfold change in ATPase activity [K0.5 (mM)] withc:
		K+	Rb+	NH4+	Na+	Li+	Cs+
Wild type	839	4.2 [0.04]	1.7 [10]	2.2 [3.9]	1.4 [15]	0.3 [15]	0.3 [55]
Q116R	406	9.2 [7.2]	1.0 [−]e	1.5 [9.9]	1.6 [27]	0.7 [35]	0.7 [75]
G232D	654	6.5 [0.50]	5.0 [3.3]	4.9 [9.1]	2.4 [27]	1.3 [18]	0.3 [50]
G232A	1,106	1.8 [150]d	0.4 [78]	1.9 [5.3]	0.8 [40]	0.3 [52]	0.3 [73]
G232S	618	0.7 [14]	0.3 [60]	1.6 [3.9]	0.8 [20]	0.6 [13]	0.3 [45]
G233Y	1,046	2.6 [0.40]	1.6 [17]	2.2 [3.6]	1.7 [18]	0.5 [28]	0.8 [70]
G233D	1,088	3.8 [0.11]	1.7 [10]	2.5 [8.4]	1.5 [32]	0.4 [31]	0.4 [29]
G233A	828	4.5 [0.08]	2.0 [7.5]	2.2 [3.7]	1.3 [21]	0.2 [15]	0.3 [60]
G233S	985	3.8 [0.12]	2.0 [10]	2.4 [6.2]	1.7 [15]	0.5 [26]	0.6 [92]
G234D	714	6.6 [0.53]	0.8 [23]	2.6 [8.8]	1.4 [22]	0.4 [18]	0.4 [46]
G234A	912	4.4 [0.10]	1.6 [15]	2.1 [4.2]	1.2 [23]	0.2 [18]	0.2 [31]
G234S	930	4.3 [0.17]	1.3 [8.1]	1.9 [7.4]	1.0 [−]e	0.3 [10]	0.3 [24]

^aThe data presented represent average values obtained in at least three independent experiments.

^bAveraged basal activity values for complexes without any cations are given in micromoles per gram per minute.

^cValues for stimulating cations are in bold letters, whereas values for inhibiting cations are in light face letters; change was measured in the presence of saturating concentrations of the different cations. Values less than 1 indicate an inhibitory effect, whereas a value of 1 represents no stimulation or inhibition. Values for cations without any effect or with only a small effect are underlines. K_0.5 values [in millimolar units) for half-maximal stimulation or inhibition are in brackets.

^dComplex G232A showed a very low affinity for K⁺ such that stimulation by K⁺ was increasingly counteracted by the inhibitory effect of high salt concentrations (>200 mM) (Fig. 1).

^e[−], K_0.5 value = 0.