The polar oxy-metabolome reveals the 4-hydroxymandelate CoQ10 synthesis pathway

Oxygen is critical for a multitude of metabolic processes that are essential for human life. Biological processes can be identified by treating cells with 18 O 2 or other isotopically labelled gases and systematically identifying biomolecules incorporating labeled atoms. Here we labelled cell lines of distinct tissue origins with 18 O 2 to identify the polar oxy-metabolome, defined as polar metabolites labelled with 18 O under different physiological O 2 tensions. The most highly 18 O-labelled feature was 4-hydroxymandelate (4-HMA). We demonstrate that 4-HMA is produced by hydroxyphenylpyruvate dioxygenase-like (HPDL), a protein of previously unknown function in human cells. We identify 4-HMA as an intermediate involved in the biosynthesis of the coenzyme Q10 (CoQ10) headgroup in human cells. The connection of HPDL to CoQ10 biosynthesis provides crucial insights into the mechanisms underlying recently described neurological diseases related to HPDL deficiencies 1 – 4 and cancers with HPDL overexpression 5 . 18 O 2 labelling is used to identify metabolites in human cells that incorporate gaseous oxygen, including 4-hydroxymandelate, an intermediate in the synthesis of the coenzyme Q10 head group.