Fig. 1 in 3-O-glycosylation of kaempferol restricts the supply of the benzenoid precursor of ubiquinone (Coenzyme Q) in Arabidopsis thaliana

Fig. 1. Metabolic origins of 4-hydroxybenzoate for ubiquinone biosynthesis in plant cells. Note that chemical modeling of the peroxidative cleavage of kaempferol predicts that peroxidases do not act on kaempferol itself, but on its α-diketone tautomer. The formation of the latter is contingent on the presence of a double bond between C-2 and C-3 and a free C-3- OH on the C-ring. Dashed arrows indicate unknown and/or multiple steps. Ara, arabinosyl; Glu, glucosyl; Rha, Rhamnosyl; UGT78D1, flavonol 3-O-rhamnosyltransferase; UGT78D2, flavonol 3-O-glucosyltransferase; UGT78D3, flavonol 3-O- arabinosyltransferase.