An organic O donor for biological hydroxylation reactions

All biological hydroxylation reactions are thought to derive the oxygen atom from one of three inorganic oxygen donors, O₂, H₂O_2, or H₂O. Here, we have identified the organic compound prephenate as the oxygen donor for the three hydroxylation steps of the O₂-independent biosynthetic pathway of ubiquinone, a widely distributed lipid coenzyme. Prephenate is an intermediate in the aromatic amino acid pathway and genetic experiments showed that it is essential for ubiquinone biosynthesis in Escherichia coli under anaerobic conditions. Metabolic labeling experiments with ¹⁸O-shikimate, a precursor of prephenate, demonstrated the incorporation of ¹⁸O atoms into ubiquinone. The role of specific iron-sulfur enzymes belonging to the widespread U32 protein family is discussed. Prephenate-dependent hydroxylation reactions represent a unique biochemical strategy for adaptation to anaerobic environments.