Table 4.
Comparison of catalytic activities of mouse Cyp17a1 wild-type and mutants.
| mouse Cyp17a1 | b 5 | Progesterone 17α-hydroxylation | 17α-OH progesterone conversion to androstenedione | ||||||
|---|---|---|---|---|---|---|---|---|---|
| kcat, min−1 | Km, μM | kcat/Km | % WT (kcat/Km) | kcat, min−1 | Km, μM | kcat/Km | % WT (kcat/Km) | ||
| WT | + | 5.42 ± 0.30 | 0.25 ± 0.05 | 23 ± 6 | 100 | 15.7 ± 1.19 | 0.42 ± 0.09 | 40 ± 11 | 100 |
| R347H | 1.58 ± 0.16 | 0.15 ± 0.03 | 11 ± 3 | 49 | 2.86 ± 0.16 | 0.21 ± 0.05 | 15 ± 4 | 36 | |
| R358Q | 1.56 ± 0.08 | 0.11 ± 0.03 | 16 ± 5 | 68 | 1.56 ± 0.08 | 0.09 ± 0.05 | 26 ± 15 | 64 | |
| mouse Cyp17a1 | b 5 | Pregnenolone 17α-hydroxylation | 17α-OH pregnenolone conversion to DHEA | ||||||
| kcat, min−1 | Km, μM | kcat/Km | % WT (kcat/Km) | kcat, min−1 | Km, μM | kcat/Km | % WT (kcat/Km) | ||
| WT | + | 4.35 ± 0.23 | 0.44 ± 0.07 | 10 ± 2 | 100 | 0.47 ± 0.02 | 0.38 ± 0.06 | 1.28 ± 0.25 | 100 |
| R347H | 1.38 ± 0.07 | 0.34 ± 0.06 | 4.2 ± 1.0 | 41 | 0.14 ± 0.01 | 0.47 ± 0.07 | 0.35 ± 0.03 | 27 | |
| R358Q | 2.41 ± 0.18 | 0.56 ± 0.13 | 4.6 ± 1.4 | 45 | ND | ND | ND | ND | |
a
Not determined. In the presence of cytochrome b5, the 17α-OH lyase reaction did not detect any product (DHEA) until the maximum substrate concentration.