Table 1.
Degree of regiospecificity (dominant, moderate, weak or no) of various UGT (uridine diphosphate glucuronosyltransferases) isoforms for glucuronidating flavones and flavonols. The position shown in bracket stands for major glucuronide. In case of di-hydroxyflavones and hydroxyflavonols, degree of regiospecificity was determined based on ratio of rates of formation of two glucuronides. In case of tri-hydroxyflavones, di-hydroxyflavonols and tri-hydroxyflavonols, degree of regiospecificity was determined based on ratio of rates of formation of two faster glucuronides.
| UGT Isoforms | Substrate Concentration (μM) | 4'HFnol | 7HFnol | 5,4'DHF | 5,7DHF | 7,4'DHF | 5,7DHFnol1 | 7,4'DHFnol1 | 5,7,4'THF2 | 5,7,4'THFnol1 |
|---|---|---|---|---|---|---|---|---|---|---|
| 1A1 | 2.5 | No (3-O, 4’-O) | Weak (7-O) | Dominant (4’-O) | Dominant (7-O) | Weak (7-O) | Weak (7-O) | No (3-O, 7-O) | Dominant (7-O) | Weak (7-O) |
| 10 | No (3-O, 4’-O) | No (3-O,7-O) | Dominant (4’-O) | Dominant (7-O) | Moderate (7-O) | Weak (7-O) | No (3-O, 7-O) | Dominant (7-O) | No (3-O, 7-O) | |
| 1A3 | 2.5 | Dominant (3-O) | Moderate (7-O) | Dominant (4’-O) | Dominant (7-O) | Dominant (7-O) | Dominant (7-O) | Dominant (7-O) | Dominant (7-O) | No (3-O, 7-O) |
| 10 | No (3-O, 4’-O) | Dominant (7-O) | Moderate (4’-O) | Dominant (7-O) | Dominant (7-O) | Dominant (7-O) | Weak (7-O) | Dominant (7-O) | No (3-O, 7-O) | |
| 1A6 | 2.5 | Dominant (3-O) | * | * | Moderate (7-O) | * | - | * | Dominant (7-O) | Moderate (3-O) |
| 10 | Dominant (3-O) | * | * | Moderate (7-O) | Dominant (7-O) | # | * | Dominant (7-O) | ## | |
| 1A7 | 10 | Dominant (3-O) | Dominant (3-O) | * | Dominant (7-O) | * | Dominant (3-O) | * | Dominant (7-O) | Weak (3-O) |
| 1A8 | 2.5 | Dominant (3-O) | Moderate (3-O) | Dominant (4’-O) | Dominant (7-O) | Dominant (7-O) | Dominant (3-O) | * | Dominant (7-O) | Weak (3-O) |
| 10 | Dominant (3-O) | Moderate (3-O) | Moderate (4’-O) | Dominant (7-O) | Moderate (7-O) | Moderate (3-O) | * | Dominant (7-O) | Weak (3-O) | |
| 1A9 | 2.5 | Dominant (3-O) | Moderate (3-O) | Dominant (4’-O) | Dominant (7-O) | Moderate (7-O) | Weak (3-O) | Moderate (3-O) | Dominant (7-O) | Moderate (3-O) |
| 10 | Dominant (3-O) | Moderate (3-O) | Dominant (4’-O) | Dominant (7-O) | Moderate (7-O) | No (3-O, 7-O) | Moderate (3-O) | Dominant (7-O) | Weak (3-O) | |
| 1A10 | 2.5 | No (3-O, 4’-O) | Weak (3-O) | Dominant (4’-O) | Dominant (7-O) | Dominant (7-O) | Dominant (3-O) | * | Dominant (7-O) | Moderate (3-O) |
| 10 | Dominant (3-O) | No (3-O, 7-O) | Dominant (4’-O) | Moderate (7-O) | No (7-O, 4’-O) | # | No (3-O, 7-O) | Dominant (7-O) | Weak (3-O) | |
| 2B7 | 10 | Dominant (3-O) | Dominant (7-O) | Dominant (4’-O) | Moderate (7-O) | * | # | Weak (3-O) | Dominant (7-O) | ## |
stands for ratio of rates of formation of 3-O and 7-O glucuronides.
stands for ratio of rates of formation of 5-O and 7-O glucuronides.
No glucuronidation was detected at any hydroxyl group.
Two faster glucuronides were 3-O and 5-O, instead of 3-O and 7-O.
Two faster glucuronides were 4’-O and 7-O, instead of 3-O and 7-O.
The highlighted cells in the table represent any change in regiospecificity with change from lower (2.5μM) to higher (10μM) substrate concentration.