Kinetic constants of the irreversible inactivation of the human wild-type and mutant UGT1*6 by 2,3-butanedione and diethyl pyrocarbonate
| Enzyme | 2,3-Butanedione | Diethyl pyrocarbonate | ||
|---|---|---|---|---|
| ki ′ | n | ki ′ | n | |
| m −1 ·min−1 | m −1 ·min−1 | |||
| UGT1*6 | 1.87 | 0.97 | 2645 | 1.3 |
| H54A | N.D. | N.D. | 2136 | 0.86 |
| R52A | 1.64 | 1.10 | N.D. | N.D. |
The enzymes were inactivated by 2,3-butanedione, as indicated in the legend of Fig. 4, or by diethyl pyrocarbonate, as previously reported (10). The second-order inactivation rate constant (ki′) for 2,3-butanedione or for diethyl pyrocarbonate was calculated from the slope of the plot of the pseudo-first-order inactivation rate constants (ki ) as a function of inhibitor concentration. The inactivation reaction order (n) with respect to inhibitor concentration [I] was calculated using the equation logki = n · log[I] + logki′.
N.D., not determined (not applicable).