Table 1.
Kinetic constants of SDR16C enzymes
Kinetic constants for each enzyme were determined using the same preparation of microsomes containing the corresponding enzyme; therefore, the differences in the catalytic rates of each enzyme towards various substrates and cofactors reflect the properties of the enzymes rather than differences in protein expression levels. UD, undetectable under the conditions of the assay; ND, not determined. The activity of murine RDHE2 toward 10 μm all-trans-retinol in the presence of 1 mm NAD+ was not detectable with up to 10 μg of RDHE2 microsomal preparation.
| SDR | Substrate/Cofactor | Apparent Km | Apparent Vmax | Vmax/Km |
|---|---|---|---|---|
| μm | nmol·min−1·mg−1 | |||
| Xenopus rdhe2 | All-trans-retinol | 0.6 ± 0.1 | 19.5 ± 0.6 | 32.5 |
| NAD+ | 108 ± 27 | 21 ± 1 | ||
| All-trans-retinaldehyde | 0.6 ± 0.1 | 3.6 ± 0.1 | 6 | |
| NADH | 8.4 ± 1.7 | 4.1 ± 0.2 | ||
| 11-cis-Retinol | 3.3 ± 0.4 | 3.9 ± 0.2 | 1.8 | |
| RDHE2 (SDR16C5) | All-trans-retinol | UD | UD | |
| All-trans-retinaldehyde | N.D. | N.D. | ||
| RDHE2S (SDR16C6) | All-trans-retinol | 0.87 ± 0.21 | 8.7 ± 0.6 | 10 |
| NAD+ | 460 ± 30 | 5.8 ± 0.2 | ||
| All-trans-retinaldehyde | 3.9 ± 0.2 | 5.4 ± 0.1 | 1.4 | |
| NADH | 11 ± 3 | 2.6 ± 0.1 | ||
| 11-cis-Retinol | 0.86 ± 0.14 | 1.34 ± 0.07 | 1.6 | |
| 9-cis-Retinol | UD | UD |