TABLE 4

Kinetic parameters of nifedipine oxidation by recombinant P450 3A enzymes and tissue microsomes from marmosets, cynomolgus monkeys, and humans

Kinetic parameters were determined by nonlinear regression analysis (mean ± standard error, n = 12 points of substrate concentrations of 1.1–200 μM) using the equation v = Vmax × [S]/(Km + [S]) for Michaelis-Menten or v = Vmax × [S]n/(S50 n + [S]n) for Hill equation (Emoto et al., 2001; Okada et al., 2009). Units of enzyme activities for tissue microsomes and recombinant P450 proteins are nmol/min/mg protein and nmol/min/nmol of P450, respectively. Units of Vmax/Km for tissue microsomes and recombinant P450 proteins are ml/min/nmol and ml/min/mg protein, respectively. The units of Km and S50 values are μM.

Enzyme SourceKm or S50naVmaxVmax/Km
Microsomes
 Marmoset liver42 ± 110 ± 10.24
 Cynomolgus monkey liver27 ± 11.4 ± 0.19.5 ± 0.20.35
 Human liver17 ± 11.1 ± 0.14.2 ± 0.10.25
 Marmoset small intestine84 ± 61.3 ± 0.12.2 ± 0.10.026
 Cynomolgus monkey small intestine37 ± 11.1 ± 0.13.2 ± 0.10.086
 Human small intestine24 ± 21.1 ± 0.12.6 ± 0.10.11
P450
 Marmoset 3A4 ortholog33 ± 477 ± 32.3
 Marmoset 3A5 ortholog37 ± 101.5 ± 0.43.3 ± 0.40.089
 Marmoset 3A90190 ± 401.3 ± 0.154 ± 70.28
 Cynomolgus monkey 3A431 ± 594 ± 53.0
 Cynomolgus monkey 3A535 ± 41.4 ± 0.1138 ± 73.9
 Human 3A452 ± 21.6 ± 0.1123 ± 22.4
 Human 3A578 ± 62.3 ± 0.2121 ± 71.6
  • a n represents the Hill coefficient.