TABLE 4.

Steady-state parameters for AMP formation in the presence of norvaline

Data were measured by aminoacyl-adenylate synthesis assay. The values represent the best fit value ± S.E. of three independent experiments.

EcLeuRS	−tRNA			+tRNAa
	Km(Nva)	kcat	kcat/Km	Km(Nva)	kcat	kcat/Km
	mm	s−1	mm−1 s−1	mm	s−1	mm−1 s−1
WT	3.6 ± 0.6	0.20 ± 0.01	0.05b	4.5 ± 0.5	6.2 ± 0.2	1.4c
D345A	3.7 ± 0.1	0.17 ± 0.01	0.05b	3.1 ± 0.8	0.23 ± 0.02	0.07b
T252R/D345A	4.3 ± 0.5	0.25 ± 0.01	0.06b	2.9 ± 0.4	0.23 ± 0.01	0.08b

^a tRNA^Leu was present at 15 μm concentration.

^b The enzymes were assayed at 0.5 μm concentration, and norvaline concentration was varied over the range 0.1–10 times the K_m value.

^c The enzymes were assayed at 25 nm.