Catalyzes the hydroxylation of 2-polyprenyl-3-methyl-6-methoxy-1,4-benzoquinol (DMQH2) during ubiquinone biosynthesis (By similarity). Has also a structural role in the COQ enzyme complex, stabilizing other COQ polypeptides (By similarity). Involved in lifespan determination in a ubiquinone-independent manner (By similarity) (PubMed:9020081, PubMed:25961505). Plays a role in modulating mitochondrial stress responses, acting in the nucleus, perhaps via regulating gene expression, independent of its characterized mitochondrial function in ubiquinone biosynthesis (PubMed:25961505). Plays a role in modulating polyribosome formation (PubMed:30198021). a 6-methoxy-3-methyl-2-all-trans-polyprenyl-1,4-benzoquinol + AH2 + O2 = A + a 3-demethylubiquinol + H2O Binds 2 iron ions per subunit. Cofactor biosynthesis; ubiquinone biosynthesis. Component of a multi-subunit COQ enzyme complex. Worms show deregulation timing of a wide range of physiological processes. This leads to an average lengthening of the worm's early cell cycles, the embryonic and postembryonic development, and the period of rhythmic adult behaviors. Belongs to the COQ7 family.