Demethoxyubiquinone hydroxylases (DMQH) are members of the ferritin-like, diiron-carboxylate family which are present in eukaryotes (the CLK-1/CAT5 family) and prokaryotes (the Coq7 family). DMQH participates in one of the last steps of ubiquinone biosysnthesis and is responsible for DMQ hydroxylation, resulting in the formation of hydroxyubiquinone, a precursor of ubiquinone. CLK-1 is a mitochondrial inner membrane protein and Coq7 is a proposed interfacial integral membrane protein. Mutations in the Caenorhabditis elegans gene clk-1 affect biological timing and extend longevity. The conserved residues of a diiron center are present in this domain.