Enzyme kinetic parameters for aldehyde oxidase- and xanthine oxidase-catalyzed reactions in pooled human liver cytosol
Values represent the mean (±standard error) of triplicate determinations.
Reaction | Model | KM | Vmax | KS | r2 |
|---|---|---|---|---|---|
| μM | pmol/min/mg | μM | |||
| Aldehyde oxidase | |||||
| Phthalazine → 1-phthalazinone | Substrate inhibition | 2.6 (±0.3) | 1800 (±600) | 280 (±40) | 0.988 |
| Vanillin → vanillic acid | Michaelis-Menten | 2.7 (±0.4) | 2400 (±100) | N/A | 0.980 |
| Nicotine-Δ1′(5′)-iminium ion → cotinine | Michaelis-Menten | 0.85 (±0.13) | 5300 (±100) | N/A | 0.964 |
| CP-544,439 → CP-544,439 amide | Substrate inhibition | 58 (±3) | 2.4 (±0.1) | 1000 (±100) | 1.000 |
| Xanthine oxidase: | |||||
| Pterin → isoxanthopterin | Michaelis-Mentena | 34 (±8) | 28 (±2) | N/A | 0.999 |
↵ a The pterin oxidation enzyme kinetic data could be fit to a two-enzyme model in which the second activity had a KM value in excess of the highest concentration tested and an intrinsic clearance of 0.087 μl/min/mg.