| Coenzyme Q (Q) is a lipid component of cell membranes, and it plays a central role as an electron carrier in the mitochondrial respiratory chain in eukaryotes. The current study investigates the role of Coq6, a predicted flavin-dependent monooxygenase, in Saccharomyces cerevisiae Q6 biosynthesis. Coq6 has a 21% sequence identity to UbiH, an enzyme that is required for the hydroxylation of 2-octaprenyl-6-methoxyphenol in Escherichia coli Q8 biosynthesis. Consequently, it was postulated that Coq6 may catalyze the analogous step in S. cerevisiae Q6 biosynthesis, the hydroxylation of 2-hexaprenyl-6-methoxyphenol. It was also hypothesized that Coq6 may hydroxylate 3-hexaprenyl-4-hydroxybenzoate, an earlier intermediate in Q6 biosynthesis. The current study investigates the endogenous substrate(s) of S. cerevisiae Coq6 by HPLC analysis of radiolabeled lipid extracts from select coq6 mutants. Two amino acid residues required for Coq6 function (G39 and G199) were also identified. |
