Table 2.
Activities of purified MtIOMTs against a range of phenolic substratesa
| Substrate | MtIOMT1 | MtIOMT2 | MtIOMT3 | MtIOMT4 | MtIOMT5 | MtIOMT6 | MtIOMT7 | MsI7OMT |
|---|---|---|---|---|---|---|---|---|
| Isoflavone | ||||||||
| 6,7,4′-trihydroxyisoflavone | 43.9 (7) | 35.3 (7) | 100 (7) | 0 | 0 | 0 | 0 | 51.8 (7) |
| 6,7′-dihydroxy, 4′- methoxyisoflavone |
≤1 | 0 | 0 | 0 | 0 | 0 | 0 | ≤1 |
| 7,3′,4′-trihydroxyisoflavone | 40.8 (7) | 43.1 (7) | 52.9 (4’) | 0 | 0 | 0 | ≤1 | 47.1 (7) |
| Daidzein | 20.6 (7) | 100 (7) | ≤1 | 0 | 0 | 0 | 0 | 21.6 (7) |
| Genistein | 49.2 (7) | 61 (7) | 73.7 (4’) | 0 | 0 | 0 | 0 | 15(7) |
| Glycitein | 100 (7) | 38.9 (7) | 51.6 (7) | 0 | 0 | 0 | ≤1 | 100 (7) |
| Isoflavanone | ||||||||
| 2,7,4′-trihydroxyisoflavanone | NDc | NDc | NDc | NDc | 100 (4′) | NDc | 24.8 (4′) | NDc |
| Dihydrodaidzein | 15.6 (7) | 70.1 (7,4′) | 49.4 (4′) | 0 | 7.9 (4′,7) | 100 (4′,7) | 84.1 (4′,7) | 12.8 (7) |
| Isoflavan | ||||||||
| Vestitol | 0 | ≤1 | 0 | 43.8 | ≤1 | 66.2 | 3.4 | 0 |
| Coumestan | ||||||||
| Coumestrol | 0 | ≤1 | 0 | 100 (3,9) | 0 | 0 | 1.5 | 0 |
| Flavanone | ||||||||
| Liquiritigenin | 0 | ≤1 | 0 | 0 | ≤1 | 0 | 42.2 (4′,7) | 0 |
| Naringenin | 0 | ≤1 | 0 | 0 | ≤1 | 0 | 100 (4′) | 0 |
| Flavone | ||||||||
| Apigenin | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 7,4′-dihydroxyflavone | 0 | ≤1 | 0 | 0 | 0 | 0 | 0 | 0 |
| Flavonol | ||||||||
| Myricetin | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| pkat/mgb | 3646.7 | 930.2 | 7.4 | 2.6 | 4189.6 | 6.9 | 198.8 | 2742.0 |
a
Relative activity at 50 µM S-adenosyl methionine and 100 µM acceptor substrate. Reactions were run for several different time periods to ensure reaction rates were in the linear portion with respect to time, and values are normalized with the conversion rate for the most converted substrate as 100%. Numbers in parentheses represent the position of methylation of major products where known.Structures of the substrates, with positions of hydroxyl and methoxyl substitutions marked, are shown in Table 1
b
Specific activity at 100%
c
Not determined – initial activity screens revealed very low or no activity