Table 1.

Summary of kinetic constants for transport activity of MetNIQ variants

MetNIQ variants	Uptake rate Vmax*	Km, µM
MetNIQ	6.3 ± 0.4	1.8 ± 0.4
MetNI	0.2 ± 0.1	N/A
N295A (EcN) MetNIQ	10 ± 0.5	1.7 ± 0.3
N229A (EcQ) MetNIQ	10.5 ± 0.9	7.4 ± 0.5
N295A, N229A MetNIQ	15.4 ± 1.3	4.8 ± 0.7
N295A, F103A (EcI) MetNIQ	—	—
N295A, M107A (EcI) MetNIQ	—	—
N295A, Y160A (EcI) MetNIQ	14.0 ± 1.3	4.1 ± 0.2
N295A, M163A (EcI) MetNIQ	4.7 ± 0.5	1.4 ± 0.2

The maximum uptake rate (V_max) and Michaelis–Menten constant (K_m) were determined from the plot shown in Fig. 1B. N/A, not applicable; dash, not detectable. The molar ratio of the MetQ:MetNI variants in these studies was measured to be ∼4.

^*nmol⋅min⁻¹⋅mg⁻¹ of transporter.