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 Consumed^a.

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

^aNitrogen-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, K_m and V_max were obtained from nonlinear correlations of Michaelis-Menten plots shown in Figure 3.

^bDetermined 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.

^cInitial rates of NO consumption used to obtain K_m and V_max 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.

^dErrors in V_max and K_m are those obtained from the corresponding nonlinear regressions.

^eGoodness-of-fit values of Michaelis-Menten plot regressions.

^fMol ratios of N₂O produced to NO consumed. Errors are of the means of three determinations.