Table 1.

Kinetic parameters of GS-DCBN formation catalyzed by human and mouse nasal mucosa microsomes^a

Source of nasal mucosa	Km (μM)	Vmax (pmol/min/mg protein)	Vmax/Km (μl/min/mg)
WT mouse	0.43 ± 0.04	1050 ± 30	2440
Cyp2a5-null mouse	4.2 ± 0.6	253 ± 12	60
Human fetus	0.45 ± 0.10b	0.14 ± 0.01	0.31

^aComplete reaction mixtures contained 50 mM phosphate buffer, pH 7.4, DCBN at various concentrations, added in 1 μl methanol, 0.1 mg/ml (for mouse nasal mucosa) or 0.5 mg/ml (for human nasal mucosa) microsomal protein, 5 mM GSH, and 1 mM NADPH, in a final volume of 0.1 ml. The reaction was carried out at 37°C for 5 or 10 min (for mouse nasal mucosa) or 60 min (for human nasal mucosa). DCBN concentrations used were 0.05, 0.10, 0.25, 0.50, 1.0, 2.0, and 4.0 μM for WT mouse nasal mucosa; 0.50, 1.0, 2.0, 4.0, 8.0, 15, and 30 μM for Cyp2a5-null mouse nasal mucosa; and 0.10, 0.25, 0.50, 1.0, 2.0, 4.0, 8.0, and 15 μM for human nasal mucosa. Microsomal samples were prepared from pooled tissues from 10–12 mice (male and female, 2–3 month old) or from 8 human fetuses (male and female, 104–120 gestational days). Values represent means ± SE for three determinations.

^bP>0.05, compared to WT mouse, Student t-test