TABLE 3.

Kinetic parameters for Na⁺-dependent ethidium efflux by NorM-VC

Protein	Ethidium		Na+
	Kta	Vmaxa	Ktb	Vmaxb
	μm	a.u./s	mm	a.u./s
WT	2.62 ± 0.17	0.27 ± 0.02	0.073 ± 0.004	0.10 ± 0.01
N174A	2.71 ± 0.93	0.26 ± 0.02	8.8 ± 1.7c	0.08 ± 0.03
F288A	2.86 ± 0.51	0.21 ± 0.01	0.37 ± 0.10d	0.05 ± 0.01
Y367A	2.58 ± 0.03	0.18 ± 0.02	0.08 ± 0.03	0.05 ± 0.01
F395A	24.2 ± 10.4e	0.22 ± 0.05	0.10 ± 0.03	0.03 ± 0.01
D371N	2.60 ± 0.24	0.04 ± 0.00	0.09 ± 0.03	0.02 ± 0.00

^a Apparent K_t and V_max values were determined in a facilitated ethidium efflux assay in ATP-depleted lactococcal cells at a fixed concentration of 1 mm Na⁺.

^b Apparent K_t and V_max values were determined in a facilitated ethidium efflux assay in ATP-depleted lactococcal cells at a fixed concentration of 2 μm ethidium.

^c Significantly different substrate binding affinity compared to WT, p < 0.01.

^d Significantly different substrate binding affinity compared to WT, p < 0.05.

^e Significantly different substrate binding affinity compared to WT, p < 0.02.