TABLE 4

Kinetic parameters for 5-FU formation from R- and S-FT mediated by wild-type CYP2A6 and its variants

The kinetic parameters were calculated by nonlinear regression analysis. Each kinetic value represents the estimated value ± S.E.

EnantiomerEnzyme (Amino Acid Alteration)Kinetic Parameters
VmaxKmCLintFold Changed
pmol/min per pmol CYP2A6mMnl/min per pmol CYP2A6
R-FTCYP2A6.1 (wild-type)9.1 ± 0.20.16 ± 0.01581.0
CYP2A6.7 (I471T)1.0 ± 0.0**0.23 ± 0.01**4.20.072
CYP2A6.8 (R485L)6.9 ± 0.1**0.48 ± 0.01**140.25
CYP2A6.10 (I471T and R485L)0.47 ± 0.02**0.64 ± 0.03**0.730.013
CYP2A6.11 (S224P)6.1 ± 0.3**0.76 ± 0.05**8.00.14
HLMsa707 ± 30b0.13 ± 0.015.3cN.A.
439 ± 63b2.0 ± 0.50.22cN.A.
S-FTCYP2A6.1 (wild-type)9.8 ± 0.41.3 ± 0.17.71.0
CYP2A6.7 (I471T)0.88 ± 0.04**1.5 ± 0.10.600.077
CYP2A6.8 (R485L)6.2 ± 0.4**3.6 ± 0.3**1.70.23
CYP2A6.10 (I471T and R485L)0.31 ± 0.07**6.6 ± 1.9*0.0460.0060
CYP2A6.11 (S224P)4.4 ± 0.4**6.6 ± 0.7**0.670.087
HLMs1072 ± 34b1.6 ± 0.10.67cN.A.

  • N.A., not available.

  • ↵a The conversion of R-FT to 5-FU followed biphasic kinetics in HLMs.

  • ↵b pmol/min per mg protein.

  • ↵c μl/min per mg protein.

  • ↵d The ratio of CLint (Vmax/Km) in each CYP2A6 variant to that in CYP2A6.1.

  • ↵* P < 0.05; **P < 0.01 versus wild-type enzyme.