TABLE 2.

Steady-state deacylation of aminoacyl-tRNAs

The values represent the mean value ± S.E. of at least two independent experiments. Aminoacyl-tRNA was present at 6–8 μm concentration.

EcLeuRS	kobsa
	Nva-tRNALeu	Ile-tRNALeu	Leu-tRNALeu
	s−1
WT	5.8 ± 0.5b	2.07 ± 0.05c,d	(10 ± 3) × 10−3e
D345A	(1.4 ± 0.1) × 10−3f	NDg	ND
T252R	0.38 ± 0.02h	(3.3 ± 0.3) × 10−3f	(3.8 ± 0.1) × 10−3f
T252R/D345A	(0.6 ± 0.1) × 10−3f	ND	ND

^a k_obs values were corrected for nonenzymatic hydrolysis of aminoacyl-tRNA. Because saturation was established for aminoacyl-tRNA, these values are equivalent to k_cat.

^b The enzymes were assayed at 2.5 nm concentration.

^c The enzymes were assayed at 3 nm concentration.

^d A similar value was obtained with a separate preparation of [¹⁴C]Ile-tRNA^Leu.

^e The enzymes were assayed at 100 nm concentration.

^f The enzymes were assayed at 500 nm concentration.

^g ND means not determined because activity was too low for reliable detection.

^h The enzymes were assayed at 20 nm concentration.