Table 3.
CLint, RAF for CYP isoforms, and contributions (%) to the enantioselective conversion of FT to 5-FU
| CYP isoform (reported Km value) | Metabolism of probe substrates | 5-FU formation from FT | |||||
|---|---|---|---|---|---|---|---|
| CLint (μL min−1 mg−1) hepatic microsomes | CLint (nL min−1 pmol−1 CYP) recombinant CYP isoforms | RAF | Velocity (pmol min−1 pmol−1 CYP) | CYP contribution (%) | |||
| R-FT | S-FT | R-FT | S-FT | ||||
| CYP1A2 (30 μmol/L)1 | 151 ± 3 | 1.93 ± 0.08 | 78.2 | 145 ± 20 | 16.0 ± 3.4 | 7.5 | 4.4 |
| CYP2A6 (4.4 μmol/L)2 | 860 ± 4 | 5.28 ± 0.11 | 163 | 815 ± 48 | 149 ± 10 | 87.6 | 84.8 |
| CYP2C19 (70 μmol/L)3 | 9.11 ± 0.38 | 0.179 ± 0.008 | 50.9 | 17.5 ± 3.2 | 21.7 ± 0.8 | 0.59 | 3.9 |
| CYP2E1 (87 μmol/L)2 | 228 ± 5 | 1.80 ± 0.02 | 126 | 52.1 ± 2.7 | 15.8 ± 0.3 | 4.3 | 7.0 |
Refer to the experimental section for probe substrates used for estimating the metabolic activity of particular CYP isoforms. The reaction velocity of 5-FU formation from R- and S-FT was determined using recombinant CYP isoforms as the enzyme source. Each value shown is the average of triplicate determinations (mean ± SD). RAF, CLint of CYPn in microsomes/CLint of cDNA-expressed CYPn; CYP contribution (%), RAF × (VCYPn)/(VCYPn) × 100 where V is the velocity in recombinant CYP-mediated conversion of FT to 5-FU. See also the Material and Methods for the detail.
1
Bourrié et al. (1996).
2
Bogarrds et al. (2000).
3
Coller et al. (1999).