The function of Ensembl gene identifier ENSG00000119723 (COQ6, coenzyme Q6, monooxygenase) is as follows. FAD-dependent monooxygenase required for two non-consecutive steps during ubiquinone biosynthesis (PubMed:26260787, PubMed:38425362). Required for the C5-ring hydroxylation during ubiquinone biosynthesis by catalyzing the hydroxylation of 4-hydroxy-3- (all-trans-decaprenyl)benzoic acid to 3,4-dihydroxy-5-(all-trans- decaprenyl)benzoic acid (PubMed:26260787, PubMed:38425362). Also acts downstream of COQ4, for the C1-hydroxylation during ubiquinone biosynthesis by catalyzing the hydroxylation of 2-methoxy-6-(all-trans- decaprenyl)phenol to 2-methoxy-6-(all-trans-decaprenyl)benzene-1,4-diol (PubMed:38425362). The electrons required for the hydroxylation reaction are funneled indirectly to COQ6 from NADPH via a ferredoxin/ferredoxin reductase system composed of FDX2 and FDXR (PubMed:26260787, PubMed:38425362). {ECO:0000269|PubMed:26260787, ECO:0000269|PubMed:38425362}.