TABLE 2.
Enzyme kinetic parameters of tryptophan hydroxylase one in the absence and presence of omeprazole.
| [Omeprazole] (µM) | Vmax (µmol/min/mg) | KM (µM) | |
|---|---|---|---|
| (A) L-Trp (0.625–20) µM BH4 200 µM | 0 | 26.23 (24.35–28.12) | 1.90 (1.43–2.38) |
| 1 | 24.96 (23.18–26.74) | 2.24 (1.71–2.77) | |
| 10 | 21.08 (18.84–23.32) | 3.61 (2.51–4.72) | |
| 100 | 7.03 (6.07–7.98) | 2.05 (1.10–2.99) | |
| (B) BH4 (2.4–200) μM L-Trp 20 µM | 0 | 48.36 (45.94–50.78) | 13.66 (11.09–16.24) |
| 1 | 39.93 (37.18–42.69) | 20.40 (15.57–25.25) | |
| 10 | 31.06 (28.90–33.21) | 25.55 (19.77–31.33) | |
| 100 | 21.11 (18.96–23.26) | 32.43 (22.3–42.55) |
(A) TPH1 activity was measured as a function of L-Trp concentration in the absence (DMSO vehicle) or presence of omeprazole (at 1, 10, and 100 µM) and 200 µM BH4. (B) TPH1 activity was measured as a function of BH4 concentration in the absence (DMSO vehicle) or presence of omeprazole (at 1, 10, and 100 µM) and 20 μM L-Trp. Values in brackets represent 95% confidence intervals for the fit of the Michaelis–Menten equation to data.