TABLE 1

Steady-state kinetic constants for R-, S-, and rac-warfarin reduction by human liver cytosol

Substrate	Metabolite	Best-Fit Model^{^a}	V_max (pmol/min/mg protein)	K_m (µM)	Efficiency (V_max/K_m)
R-warfarin	RS-warfarin alcohol	Michaelis-Menten	155 ± 18	710 ± 160	0.22
R-warfarin	RR-warfarin alcohol	Michaelis-Menten	0.63 ± 0.18	560 ± 330	0.0011
S-warfarin	SR-warfarin alcohol	NA^{^b}	NA^{^b}	NA^{^b}	NA^{^b}
S-warfarin	SS-warfarin alcohol	Michaelis-Menten	41 ± 18	3500^{^c}	0.012
Rac-warfarin	Alcohol 2 (RS/SR-warfarin alcohols)	Michaelis-Menten	78 ± 10	710 ± 170	0.11
Rac-warfarin	Alcohol 1 (RR/SS-warfarin alcohols)	Michaelis-Menten	4.8 ± 0.7	330 ± 130	0.015
Rac-warfarin (Malátková et al., 2016)	Alcohol 2 (RS/SR-warfarin alcohols)	Michaelis-Menten	76.4 ± 6.0	746 ± 93	0.10
Rac-warfarin (Malátková et al., 2016)	Alcohol 1 (RR/SS-warfarin alcohols)	Michaelis-Menten	2.0 ± 0.2	248 ± 51	0.0080

NA, not applicable.
↵^a Best fit of data was determined between hyperbolic (Michealis-Menten) and nonhyperbolic (Hill equation) models using extra sum-of-squares F test in GraphPad Prism.
↵^b SR-warfarin alcohol was consistently quantifiable only at S-warfarin concentrations of 600 µM or greater, yet data could not be reliably fit to any kinetic model.
↵^c The predicted K_m was greater than the highest substrate concentration used in this study (1000 μM) owing to solubility limits; thus, there is more error in the kinetic constants than predicted by a fit, hence the exclusion of S.E. from the table.