Table 1.

Kinetic parameters of reactions catalyzed by the tRNA^Val-embedded enzymes and the corresponding nonembedded enzymes

	kcat, min−1	Apparent KM, μM	Apparent kcat/KM, μM−1⋅min−1
tRNAVal-embedded enzymes
d2L/R	0.00013	0.88	0.00015
d5L/R	0.057	0.028	2.0
Rz1	0.083	0.15	0.55
Rz2	0.065	0.13	0.50
Nonembedded enzymes
N-d2L/R*	0.006	1.0	0.006
N-d5L/R*	0.24	0.22	1.1
N-Rz1	0.85	0.040	21
N-Rz2	0.55	0.020	28

Rate constants were measured, in 50 mM Tris⋅HCl (pH 8.0) and 25 mM MgCl₂, under single-turn over conditions at 37°C. In the assays of Rz1 and N-Rz1, which cleaved HIV-1 tat mRNA at GUC triplet-1 (Fig. 1C), a short 16-meric substrate (S16) was used. Except in these two cases, a 19-meric short substrate (S19), which contained GUC triplet-2 of tat mRNA, was used. In the case of maxizymes, the K_M apparent appears to be a complicated quantity, which might roughly characterize the dimerization process (7). 

^*Kinetic parameters were taken from ref. 9.