An organic O donor for biological hydroxylation reactions.

Abstract

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 <i>Escherichia coli</i> 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.