Steady-state kinetics for meclofenamate metabolism

Shown are kinetic constants for the metabolism of the substrates in bold. Best-fit constants reported with 95% confidence intervals shown in parentheses.

AnalyteVmaxaKm or Kh (μM)hVmaxb/Km or KhMechanismc
Meclofenamate11,800 (10,700–13,200)166 (133–210)71.1 (51.0–99.2)Michaelis-Menten
Dechloro-ortho-quinone-imine83.2 (80.1–87.0)22.0 (18.8–25.7)1.2 (1.0–1.4)3.8d (3.1–4.6)Positive cooperativity
Monohydroxy para-quinone-imine11.5 (11.0–12.0)2.3 (1.6–3.2)5.0 (3.4–7.5)Michaelis-Menten
Dihydroxy ortho-quinone8.1 (7.5–9.0)67.4 (47.8–93.6)2.4 (1.5–4.0)0.12d (0.08–0.19)Positive cooperativity
Multi-GSH adduct4.1 (3.8–4.4)23.2 (16.5–32.0)0.18 (0.12–0.27)Michaelis-Menten
  • a pmol/min per milligram protein.

  • b pmol/min per milligram protein per micromolar.

  • c Most statistically favored kinetic mechanisms are listed.

  • d For positive cooperativity, catalytic efficiency is poor at low substrate concentration and improves at higher concentration so that there is not a single catalytic efficiency for the reaction. Nevertheless, fractional bioactivation analyses (Table 2) relied on Vmax/Kh ratio as an upper limit on a linearly dependent catalytic efficiency for bioactivation as a function of meclofenamate concentration.