Table 1.

Steady state aminoacylation kinetics of tRNA^His by human and bacterial histidyl-tRNA synthetases

	Variable Substrate
	tRNA			histidine
Enzyme	Km (μM)	kcat (s−1)	kcat/Km (μM−1 s−1)	Km (μM)	kcat (s−1)	kcat/Km (μM−1 s−1)	References
WT HARS	1.2 ± 0.5	3.9 ± 0.6	3.2 ± 1.0	8.0 ± 4.0	4.1 ± 0.4a	0.5 ± 0.4	This work
Y454S HARS	0.9 ± 0.2	4.4 ± 0.3	5.1 ± 1.0	4.7 ± 2.5	5.9 ± 0.5a	1.2 ± 0.4	This work
E. coli HisRS	0.34 ± 0.05	1.71 ± 0.06	5.0	35 ± 4b	133 ± 2b	3.8b	16

Values reported are the mean ± standard error of three independent experiments.

^aSignificantly different (extra sum-of-squares F test) p<0.05.

^bData are for histidine in the pyrophosphate exchange reaction.