Table 1. Kinetic Parameters of the X/XO Reduction of NO in the Presence of Quinones and Ratio of N2O Produced to That of NO Consumeda.
quinone | E1/2 (mV)b | Km (μM) | Vmaxc (10-8 M s-1) | R2e | N2O/NO consumed f | |
---|---|---|---|---|---|---|
PHQ | -260 | -628 | 11 ± 1 | 61 ± 3d | 0.99 | 0.26 ± 0.02 |
DMBQ | -296 | -644 | 6.8 ± 0.9 | 52 ± 3 | 0.98 | 0.26 ± 0.03 |
NQ | -326 | -684 | 5.9 ± 0.4 | 43 ± 1 | 0.99 | 0.23 ± 0.02 |
UBQ-0 | -339 | -658 | 4.6 ± 0.4 | 48 ± 2 | 0.97 | 0.26 ± 0.03 |
DMOBQ | -364 | -664 | 4.7 ± 0.9 | 44 ± 3 | 0.89 | 0.24 ± 0.03 |
MNQ | -408 | -696 | 1.6 ± 0.1 | 16.9 ± 0.2 | 0.998 | 0.20 ± 0.03 |
DQ | -524 | -708 | 0.79 ± 0.04 | 6.54 ± 0.04 | 1.0 | 0.19 ± 0.02 |
Nitrogen-saturated solutions containing 20 μM NO, 10 mU XO/mL, and 50 μM X from 0 to 20 μM quinone in 50 mM phosphate buffer (pH 7.4). Michaelis and Menten parameters, Km and Vmax were obtained from nonlinear correlations of Michaelis-Menten plots shown in Figure 3.
Determined by DPV against an Ag/AgCl reference electrode at 25 °C in acetonitrile. Left and right columns correspond to the first and second electron redox potentials, respectively.
Initial rates of NO consumption used to obtain Km and Vmax were those obtained after subtracting the basal initial rate, that is, in the absence of quinone, (6.2 ± 0.3) × 10-8 M/s’ from the measured initial rate.
Errors in Vmax and Km are those obtained from the corresponding nonlinear regressions.
Goodness-of-fit values of Michaelis-Menten plot regressions.
Mol ratios of N2O produced to NO consumed. Errors are of the means of three determinations.