Figure 1.

Pre-steady-state acid-quenched kinetics of dTTP hydrolysis. 4A′ (3.3 μM hexamer) was mixed with [α-³²P]dTTP (50–600 μM) in a rapid quench-flow instrument at 18°C, and reactions were quenched with 1 M HCl. (A) Representative dTTPase time course at 100 μM dTTP (•) is shown. The data were fit to a single exponential followed by a linear phase with a burst amplitude of 0.80 ± 0.04 dTTP per hexamer, a burst rate constant of 0.34 ± 0.04 s⁻¹, and a dTTPase turnover rate of 0.043 ± 0.0007 s⁻¹. (B) The [dTTP] dependence of the burst amplitude (▴) and the burst rate constant (•) is shown. The [dTTP] dependence of the burst rate constant fit to a hyberbola with a maximum dTTP hydrolysis rate constant of 0.66 ± 0.083 s⁻¹ and K½ of 167 ± 57 μM.