Table 3. Metabolism of EPA by recombinant Cyp4a enzymes.
n.d., Not determined.
| Km (μM) | Vmax (nmol·nmol−1·min−1) | Product distribution (%)* | Stereoselectivity (%)* | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| CYP | + cytb5 | + cytb5 | 19-HEPE | 20-HEPE | 17,18-EETeTr | EETeTr | 17(R),18(S)-EETeTr | 17(S),18(R)-EETeTr | ||
| 4a10 | n.d. | n.d. | 0.1±0.01† | 0.2±0.03† | 60‡ | 40‡ | – | n.d. | n.d. | |
| 4a12a | 29±4 | 33±2 | 14±1 | 29±1 | 12 | 32 | 56 | – | 73 | 27 |
| 4a12b | 41±5 | 62±20 | 15±1 | 30±7 | 11 | 21 | 68 | – | 51 | 49 |
| 4a14 | n.d. | n.d. | 0.02±0.01† | 0.03±0.01† | 11‡ | – | 89‡ | n.d. | n.d. | |
*The metabolites were resolved and quantified by RP-HPLC followed by NP-HPLC or chiral-phase HPLC as shown in Supplementary Figure S3. The values are averages for experiments with at least three different microsomal preparations. The standard errors were less than 10% of the mean.
†Activities of Cyp4a10 and Cyp4a14 are given for a substrate concentration of 10 μM since a detailed kinetic analysis was not possible due to the very weak activities of these isoforms towards EPA. For comparison, under the same conditions, the corresponding values for Cyp4a12a were 3.6 and 6.7 (+cytb5) nmol·nmol−1·min−1 and for Cyp4a12b 3.0 and 4.2 (+cytb5) nmol·nmol−1·min−1.
‡Estimation from RP-HPLC only.