Table 3.

Apparent steady state kinetic parameters for pyrophosphate exchange and aminoacylation catalyzed by R259H HisRS at 37°C

	Km, μM			kcat, sec−1
	His	ATP	tRNA	PPi exchange	aminoacylation
wt HisRS	30  (±5)	890  (±64)	1.4  (±0.6)	130  (±5)	2.6  (±0.4)
R259H	25  (±1)	307  (±12)	3.3  (±0.4)	0.103  (±0.010)	0.006  (±0.001)

Values shown represent the mean of at least two independent determinations. Standard errors, shown in parentheses, were obtained in the curve fits to the Michaelis–Menten equation calculated by the program enzfitter. wt, wild type.