Involvement of Mitochondrial Ferredoxin and Para-Aminobenzoic Acid in Yeast Coenzyme Q Biosynthesis

SummaryYeast ubiquinone or coenzyme Q6 (Q6) is a redox active lipid that plays a crucial role in the mitochondrial electron transport chain. At least nine proteins (Coq1p–9p) participate in Q6 biosynthesis from 4-hydroxybenzoate (4-HB). We now show that the mitochondrial ferredoxin Yah1p and the ferredoxin reductase Arh1p are required for Q6 biosynthesis, probably for the first hydroxylation of the pathway. Conditional Gal-YAH1 and Gal-ARH1 mutants accumulate 3-hexaprenyl-4-hydroxyphenol and 3-hexaprenyl-4-aminophenol. Para-aminobenzoic acid (pABA) is shown to be the precursor of 3-hexaprenyl-4-aminophenol and to compete with 4-HB for the prenylation reaction catalyzed by Coq2p. Yeast cells convert U-(13C)-pABA into 13C ring-labeled Q6, a result that identifies pABA as a new precursor of Q6 and implies an additional NH2-to-OH conversion in Q6 biosynthesis. Our study identifies pABA, Yah1p, and Arh1p as three actors in Q6 biosynthesis