Table 4.

Kinetic parameters for aminoacylation by WT and mutant variants of Ec ProRS^a

Ec ProRS	kcat/KM (relative)	Fold-Decrease	ΔΔG (kcal/mol)
WT	1	1	-
D198A	0.18	5.5	1.0
E218Ac	0.71	1.4	0.20
E234A	0.48	2.1	0.43
H302A	0.45	2.2	0.46
N305A	0.014	70	2.5
G412A	0.14	7.1	1.2
F415A	0.014	70	2.5
H302A/G412A	0.18	5.5	1.0
N305A/G412A	ND	-	-
E218A/N305A	ND	-	-

^aAminoacylation assays were performed under conditions where the initial rates were proportional to RNA concentrations. This indicated that V₀/[S] was an accurate reflection of k_cat/K_M. The relative k_cat/K_M values were normalized and set to 1 for WT. ΔΔG was calculated according to the equation ΔΔG = −RT ln (fold-decrease of k_cat/K_M), where R is the gas constant, 1.986 cal K⁻¹ mol⁻¹ and T is 298 K. ND indicates not detectable under the experimental conditions used.

^bData is from reference (16).