Table 2

Kinetic parameters for amitriptyline N-demethylation by human liver microsomes in the presence of varying amounts of heat-inactivated microsomal protein.

Parameter (eq. 3)Concentration of Heat-Inactivated Microsomal Protein Added2-c (free fraction in incubate)
0 (1.0)50 (0.88)150 (0.63)450 (0.32)
μg/ml
K m 2-a 20  ± 2223  ± 3427  ± 38122  ± 182
V max1 2-b 969  ± 772940  ± 1068892  ± 9422077  ± 2792
S50 2-a 84  ± 996  ± 13107  ± 11184  ± 17
V max2 2-b 1832  ± 7572013  ± 10562197  ± 9211581  ± 2194
A 2.2  ± 0.62.0  ± 0.62.2  ± 0.52.5  ± 1.3
UnboundK m 2-a 2020.21739.5
Unbound S50 2-a 8484.56760

Values are mean ± S.E. of parameter estimates.

  • 2-a Given as micromolar.

  • 2-b Given in picomoles per minute per milligram of protein.

  • 2-c Active protein concentration was 50 μg/ml in all cases.