TABLE 3.

Kinetic analysis with dGTP as the variable substrate^a

Enzymeb	Vmax	Km	kcat (s−1)	kcat/Km
Wild type	198 ± 2	3.55 ± 0.02	0.194 ± 0.002	0.055 ± 0.001
G190A	293 ± 3	2.42 ± 0.03	0.287 ± 0.003	0.119 ± 0.002
G190S	172 ± 3	2.29 ± 0.03	0.169 ± 0.003	0.074 ± 0.002
G190E	68 ± 2	10.46 ± 0.09	0.067 ± 0.002	0.006 ± 0.001
L74V-G190E	184 ± 4	5.18 ± 0.03	0.180 ± 0.004	0.035 ± 0.001
V75I-G190E	179 ± 3	5.27 ± 0.02	0.175 ± 0.003	0.033 ± 0.001
L74V	170 ± 3	3.31 ± 0.02	0.167 ± 0.003	0.051 ± 0.001
V75I	158 ± 4	5.23 ± 0.04	0.155 ± 0.004	0.030 ± 0.001

^aThe dGTP kinetic assays were similar to that described by Hizi et al. (14). All assays were carried out in triplicate, and the results are 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 (dGTP) versus the initial velocities of dGTP incorporation at each dGTP concentration. V_max is in units of picomoles of dGTP incorporated in 10 min; K_m is in units of micromolar dGTP. 

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