TABLE 2.
Enzyme kinetic parameters for the conversion of 6-mercaptopurine to 6-thioxanthine and 6-thioxanthine to 6-thiouric acid in pooled human liver cytosol in the presence and absence of NAD+
Data are representative of at least duplicate measurements ± S.E.M.
| Reaction | Source | Enzyme Kinetics |
Vmax
|
Km
|
||
|---|---|---|---|---|---|---|
| Vmax1 | Vmax2 | Km1 | Km2 | |||
| nmol/min per milligram | μM | |||||
| 6MP → 6TX | HLC (–NAD) | Biphasic | 0.08 ± 0.00 | 0.2 ± 0.1 | 88.2 ± 4.4 | 500 ± 188 |
| HLC (+NAD) | Biphasic | 0.2 ± 0.01 | 0.3 ± 0.1 | 83.4 ± 2.9 | 339 ± 169 | |
| 6TX → 6TUA | HLC (–NAD) | Michaelis-Menten | 7.2 ± 0.2 | NA | 3.0 ± 0.4 | NA |
| HLC (+NAD) | Michaelis-Menten | 15.5 ± 0.7 | NA | 8.0 ± 1.6 | NA | |