title: para-Aminobenzoic acid is a precursor in coenzyme Q6 biosynthesis in Saccharomyces cerevisiae.
abstract: Coenzyme Q (ubiquinone or Q) is a crucial mitochondrial lipid required for respiratory electron transport in eukaryotes. 4-Hydroxybenozoate (4HB) is an aromatic ring precursor that forms the benzoquinone ring of Q and is used extensively to examine Q biosynthesis. However, the direct precursor compounds and enzymatic steps for synthesis of 4HB in yeast are unknown. Here we show that para-aminobenzoic acid (pABA), a well known precursor of folate, also functions as a precursor for Q biosynthesis. A hexaprenylated form of pABA (prenyl-pABA) is normally present in wild-type yeast crude lipid extracts but is absent in yeast abz1 mutants starved for pABA. A stable (13)C(6)-isotope of pABA (p- amino[aromatic-(13)C(6)]benzoic acid ([(13)C(6)]pABA)), is prenylated in either wild-type or abz1 mutant yeast to form prenyl-[(13)C(6)]pABA. We demonstrate by HPLC and mass spectrometry that yeast incubated with either [(13)C(6)]pABA or [(13)C(6)]4HB generate both (13)C(6)-demethoxy-Q (DMQ), a late stage Q biosynthetic intermediate, as well as the final product (13)C(6)-coenzyme Q. Pulse-labeling analyses show that formation of prenyl-pABA occurs within minutes and precedes the synthesis of Q. Yeast utilizing pABA as a ring precursor produce another nitrogen containing intermediate, 4-imino-DMQ(6). This intermediate is produced in small quantities in wild-type yeast cultured in standard media and in abz1 mutants supplemented with pABA. We suggest a mechanism where Schiff base-mediated deimination forms DMQ(6) quinone, thereby eliminating the nitrogen contributed by pABA. This scheme results in the convergence of the 4HB and pABA pathways in eukaryotic Q biosynthesis and has implications regarding the action of pABA-based antifolates.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
authors.forename: Beth
authors.initials: B
authors.lastname: Marbois
authors.forename: Letian X
authors.initials: LX
authors.lastname: Xie
authors.forename: Samuel
authors.initials: S
authors.lastname: Choi
authors.forename: Kathleen
authors.initials: K
authors.lastname: Hirano
authors.forename: Kyle
authors.initials: K
authors.lastname: Hyman
authors.forename: Catherine F
authors.initials: CF
authors.lastname: Clarke
mesh_terms: D010129:4-Aminobenzoic Acid / Q000378:metabolism*; D055162:Biocatalysis; D002827:Chorismic Acid / Q000378:metabolism; D005800:Genes, Fungal / Q000235:genetics; D050356:Lipid Metabolism; D008190:Lyases / Q000378:metabolism; D010226:Parabens / Q000378:metabolism; D054876:Prenylation; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D014451:Ubiquinone / Q000096:biosynthesis* / Q000378:metabolism
chemical_list: D010226:Parabens; C032165:ubiquinone 6; D014451:Ubiquinone; D008190:Lyases; D002827:Chorismic Acid; C038193:4-hydroxybenzoic acid; D010129:4-Aminobenzoic Acid