Figure 16.

The chemical structure of 2,4-dihydroxybenzoic acid (2,4-DHB), 3,4-dihydroxybenzoic acid (3,4-DHB), and vanillic acid (VA) and their use as alternative benzoquinone ring precursors for CoQ biosynthesis. Of note, as mentioned in FIGURE 15. the order of Coq3-, Coq4-, and Coq6-catalyzed reactions has not been clearly established. A representative scheme of their use in the CoQ biosynthetic pathway is shown. However, it is possible that different sequences of reactions coexist or that the sequence of reactions changes depending on the availability of different precursors. See glossary for other abbreviations.