TABLE 2.

Kinetic parameters for tyrosylation of wild-type tRNA^Tyr molecules or variants by TyrRS_apm and methionylation of wild-type tRNA^Met molecules or variants by MetRS_apm^a

tRNA	Km (μM)	kcat (10−3 s−1)	kcat/Km (n-fold)	L value
Tyrosine
Wild-type molecules
Yeast (native)	0.5	126	252	0.3
Yeast (transcript)	1.7	142	83.5	1
P. falciparum	4	18.3	4.6	18
Mutated molecules
Yeast C1-G72→A1-U72	NMb	NM	NM	NM
Yeast C1-G72→G1-C72	NM	NM	NM	NM
Yeast C1-G72→A73→G73	NM	NM	NM	NM
Yeast G34→A34	1.3	7.5	5.8	14.4
Yeast G34→C34	1.4	9.3	6.6	12.6
Yeast G34→U34	1.3	8.3	6.4	13
Yeast U35→A35	16	2.5	0.16	522
Yeast U35→C35	33.3	10	0.3	278
Yeast U35→G35	9.3	1.1	0.12	696
Yeast A36→G36	20	7.3	0.36	232
Yeast A36→U36	15.4	14.9	0.96	87
Methionine
Wild-type molecules
Yeast (native)	0.13	6.6	252	0.3
Yeast (transcript)	0.74	17.4	83.5	1
E. coli (native)	0.47	47	252	0.3
Mutated molecules
Yeast C34→G34	NM	NM	NM	NM
Yeast A35→C35	NM	NM	NM	NM
Yeast U36→C36	NM	NM	NM	NM

^aL values correspond to losses of efficiency relative to yeast tRNA^Tyr transcript or yeast tRNA^Met transcript. Values of >1 correspond to gains in efficiency. Experimental errors for k_cat and K_m varied at most by 20%. Results represent averages of at least two independent experiments.

^bNM, not measurable (loss of >10⁵).