Anthocyanin Methyltransferases

Catechol-O-methyltransferase (COMT EC 2.1.1.6) is located in many tissues and catalyzes the methylation of polyphenols. The methylation is a well-established pathway in the metabolism of flavonoids such as those that undergo 3, 4 -dihydrox-ylation of ring B excreted as 3 -0-methyl ether metabohtes in rat bile. " Recently, the apparent methylation of both cyanidin-3-glucoside and cyanidin-3-sambubioside (cyanidin is an anthocyanin with a 3, 4 -dihydroxylation of ring B) to peonidin-3-glucoside and peonidin-3-sambubioside was reported in humans. In rats, this transformation occurred mainly in the liver and was catalyzed by COMT."°... 

Bailly C, Cormier F, Do CB. 1997. Characterization and activities of S-adenosyl-L-methionine cyanidin 3-glucoside 3 -0-methyltransferase in relation to anthocyanin accumulation in Vitis vinifera cell suspension cultures. Plant Sci 122 81-89. 

JONSSON, L.M.V., AARSMAN, M.E.G., POULTON, J.E., SCHRAM, A.W., Properties and genetic control of four methyltransferases involved in the methylation of anthocyanins in flowers of Petunia hybrida. Planta, 1983,160, 174-179. 

Dihydroflavonol 4-reductase (DFR) converted dihydroflavonols (3-OH-flava-nones, 32) to leucoanthocyanidins (flavan-3,4-diols, 37). The leucoanthocyanidins (flavan-3,4-diols, 37) were converted by leucoanthocyanidin dioxygenase (LDOX) to 3-hydroxy-anthocyanidins (38). Finally, 3-hydroxy-antho-cyanidins (38) were converted by three enzymes of O-methyltransferase (OMT), UDPG-flavonoid glucosyl transferase (UFGT) and rhamnosyl transferase (UFGT) to anthocyanins (39) (Fig. 8) [23,24],... 

Further substitution reactions carried out by acyltransferases (acylation of sugars) and/or methyltransferases (methoxylation of hydroxyl groups) yield different anthocyanin structures as presented on Figure 5. 

---