TABLE 2.

Kinetic parameters of ScThrRS and its variants for Thr in amino acid activation reaction

Enzyme	kcata	Kma	kcat/Km	Relative kcat/Km	Loss of catalytic efficiency
	s−1	mm	mm−1 s−1	%	-fold
WT	3.2 ± 0.1	0.22 ± 0.02	14.6	100
R52F	1.3 ± 0.1	0.23 ± 0.02	5.7	39.1	2.6
R52A	1.8 ± 0.1	0.24 ± 0.04	7.5	51.7	1.9
R52D	1.6 ± 0.2	0.26 ± 0.05	6.1	42.0	2.4
R52K	3.3 ± 0.1	0.21 ± 0.01	15.5	106.4
G145D	2.6 ± 0.2	0.22 ± 0.05	12.0	81.9	1.2
S308F	2.4 ± 0.2	0.24 ± 0.03	9.9	67.7	1.5
G356N	NMb	NM	NM	NM	NM
S457F	3.4 ± 0.2	0.33 ± 0.02	10.4	71.0	1.4
G458D	1.0 ± 0.1	2.1 ± 0.3	0.5	3.4	29.2
R461H	1.4 ± 0.1	2.9 ± 0.1	0.5	3.4	29.8
G604E	NM	NM	NM	NM	NM
P627L	NM	NM	NM	NM	NM
G685D	4.1 ± 0.3	0.25 ± 0.02	16.4	112.4
C-Δ3	3.4 ± 0.3	0.35 ± 0.03	9.7	66.6	1.5
C-Δ5	2.8 ± 0.3	0.38 ± 0.09	7.4	50.7	2.0
C-Δ10	3.1 ± 0.2	0.43 ± 0.14	7.1	48.6	2.1

^a The results are shown as the average of three independent trials ± S.D.

^b NM, activity too low to be measured.