Table 1.

Kinetic parameters for the activation of Anl and Met by the MetRS variants identified in this study and the L13G mutant

MetRS	Anl activation kcat/Km, M−1 s−1	Met activation kcat/Km, M−1 s−1	Selectivity*
wt†	-	550,000	-
L13G	170 ± 40	5,600 ± 1,500	0.03
PLL	650 ± 150	200 ± 50	3.2
NLL	410 ± 80	350 ± 70	1.2
SLL	220 ± 20	900 ± 80	0.24
CLL	520 ± 120	7,100 ± 600	0.07
PLI	410 ± 140	-	-
PIL	130 ± 40	-	-
PNL	98 ± 37	-	-
GML	47 ± 13	-	-
GIL	14 ± 3	-	-
GCL	11 ± 2	-	-

Individual k_cat and K_m values for the activation of Met and Anl are presented with EC50 values for cell-surface labeling in Table S1.

*Selectivity is defined as the ratio of k_cat/K_m for Anl to that for Met.

^†Activation parameters for wild-type MetRS are taken from ref. 30.