TABLE 2.
Michaelis Menten kinetic parameters for 4’-OH-diclofenac formation from diclofenac by recombinant CYP2C9The data are reported as means ± S.D. from experiments done on three separate days.
| −FABP1 | +FABP1 | P Valuec | |
|---|---|---|---|
| Km,apparent (μM)a | 1.4 ± 0.2 | 5.8 ± 1.5 | 0.0011, 0.0729, 0.0416 |
| Km,u (μM)b | 1.4 ± 0.1 | 0.4 ± 0.1 | 0.0355, 0.0219, 0.0658 |
| kcat (min−1)b | 14.5 ± 0.8 | 7.3 ± 0.7 | 0.0003, 0.0003, 0.0023 |
aThe apparent Km values (Km,apparent) for diclofenac were determined from fitting the Michaelis-Menten equation to the data of 4’-OH-diclofenac formation velocity as a function of nominal diclofenac concentrations in the absence (−FABP) and presence (+FABP) of 20 μM FABP1.
bThe Km,u and kcat values for diclofenac were determined from fitting the Michaelis-Menten equation to 4’-OH-diclofenac formation velocity data as a function of free diclofenac concentration in the absence (−FABP) and presence (+FABP) of 20 μM hFABP1. Unbound diclofenac concentrations were directly measured for all nominal concentrations used in incubation experiments.
cThe P value refers to whether the specific parameter estimate is different in the presence and absence of hFABP1 in a given paired experiment. The overall models that best fit the data were significantly different (P < 0.0001 for all experiments) for the nominal diclofenac-based data and for unbound diclofenac concentration-based data.