TABLE 2.

Kinetic analysis with poly(rC) · oligo(dG) as the variable substrate^a

Enzymeb	Vmax	Km	kcat (s−1)	kcat/Km
Wild type	270 ± 4	2.29 ± 0.02	0.265 ± 0.004	0.116 ± 0.003
G190A	572 ± 8	5.14 ± 0.03	0.561 ± 0.008	0.109 ± 0.002
G190S	235 ± 5	1.94 ± 0.02	0.230 ± 0.005	0.119 ± 0.003
G190E	22 ± 4	0.23 ± 0.02	0.022 ± 0.004	0.096 ± 0.003
L74V-G190E	285 ± 5	2.72 ± 0.03	0.279 ± 0.005	0.103 ± 0.003
V75I-G190E	286 ± 4	2.74 ± 0.02	0.280 ± 0.004	0.102 ± 0.002
L74V	269 ± 5	2.01 ± 0.01	0.264 ± 0.005	0.131 ± 0.004
V75I	254 ± 4	2.33 ± 0.04	0.249 ± 0.004	0.107 ± 0.004

^aThe poly(rC) · oligo(dG) kinetic assay was similar to that described by Hizi et al. (14). All assays were carried out in triplicate, and the results are the averages of the three assays ± the error range of the three assays. The K_m and V_max values were determined from the double reciprocal (Lineweaver-Burk) plots of the starting concentrations of the variable component [poly(rC) · oligo(dG)] versus the initial velocities of dGTP incorporation at each concentration. V_max is in units of picomoles of dGTP incorporated in 10 min; K_m is in units of micrograms of poly(rC) · oligo(dG) per milliliter. 

^bEnzymes other than the wild type are designated by the mutations they carry.