TABLE 2.

Steady-state kinetic constants for ATP-[³²P]PPi exchange for CHO cytosolic full length wild type and variant TyrRS

TyrRS variant	Disrupted contact	Tyr			Phea (kcat/Km)	Specificityb, Tyr/Phe
		Km	kcat	kcat/Km
		μm	s−1	s−1/μm	s−1/μm	kcat/Km
WT		15 ± 4	13 ± 2	0.85	1.4 × 10−4 ± 3.5 × 10−5	6100
W40C		510 ± 200	0.4 ± 0.14	7.9 × 10−4	7.3 × 10−8 ± 9 × 10−9	10,850
Y52H		36 ± 4	0.7 ± 0.04	0.018	5 × 10−7 ± 1 × 10−7	36,000
A74G	Hydrophobic	103 ± 45	12 ± 6	0.11	2.7 × 10−5 ± 1 × 10−5	4100
H77T	Hydrophobic	640 ± 51	0.3 ± 0.02	4.7 × 10−4	7.3 × 10−8 ± 1.4 × 10−9	6500
N82D	Hydrogen bonding with substrate	42 ± 16	5 ± 2	0.12	1.9 × 10−5 ± 1.5 × 10−6	6300
G120N	2° hydrogen bonding	1070 ± 50	1.2 ± 0.2	1.2 × 10−3	5 × 10−7 ± 4 × 10−8	2400
Y123W	2° hydrogen bonding	42 ± 2	7.3 ± 0.85	0.18	2.3 × 10−5 ± 6.2 × 10−6	7800
D122N	2° hydrogen bonding	15 ± 2	9 ± 0.7	0.6	3 × 10−5 ± 1 × 10−5	20,000
L125W	2° hydrogen bonding	12 ± 0.4	8.3 ± 1.2	0.72	1.3 × 10−4 ± 1.4 × 10−5	6000

^a k_cat/K_m was estimated using subsaturating Phe concentrations from the slope of the equation, V = k_cat [E][S]/K_m.

^b Measured in k_cat/K_m.