The hydroxylation of the C-ring and B-ring of flavonoids at the 3- and 3′positions, catalyzed by flavanone 3-dioxygenase (F3H) and flavonoid 3′-hydroxylase (F3′H), is required for the production of DHQ from NAR (Fig. 1A). The F3′Hs are cytochrome P450-dependent enzymes that could...