Table 1

Kinetic constants for S-oxidations by human FMO3 and rabbit FMO3

	Human FMO3		Rabbit FMO3
	K_m	V_max	Stereoselectivity	K_m	V_max	Stereoselectivity
	mM	nmolsulfoxide/nmol flavin · min	%	mM	nmol sulfoxide/nmol flavin · min	%
Methionine	3.7 ± 0.6	16.9 ± 3.9	90–95	6.4 ± 0.2	20.1 ± 4.0	94–100
SAC	5.0 ± 0.8	24.8 ± 2.9	90–100	7.0 ± 1.2	22.8 ± 2.9	97–100
DCVC	31.8	2.1	100	37.8	2.2	100

Kinetic constants were determined by incubating methionine (0.5–20 mM), SAC (1–20 mM), or DCVC (5–50 mM) with E. colimembrane fractions containing cDNA-expressed human or rabbit FMO3 in the presence of 2 mM NADPH. Data were determined using double reciprocal plots and are expressed as means ± S.D. (n = 2 for methionine and SAC). DCVC data are the results of one experiment. All r values >0.99. Stereoselectivity is expressed as the percentage of total sulfoxide peak area comprising one sulfoxide diastereomer.