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.
| Analyte | Vmaxa | Km or Kh (μM) | h | Vmaxb/Km or Kh | Mechanismc |
|---|---|---|---|---|---|
| Meclofenamate | 11,800 (10,700–13,200) | 166 (133–210) | 71.1 (51.0–99.2) | Michaelis-Menten | |
| Dechloro-ortho-quinone-imine | 83.2 (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-imine | 11.5 (11.0–12.0) | 2.3 (1.6–3.2) | 5.0 (3.4–7.5) | Michaelis-Menten | |
| Dihydroxy ortho-quinone | 8.1 (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 adduct | 4.1 (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.