Identification of 3-methoxy-4-hydroxy-5-hexaprenylbenzoic acid as a new intermediate in ubiquinone biosynthesis by Saccharomyces cerevisiae.

: A ubiquinone-deficient mutant strain of Saccharomyces cerevisiae, 26H, was found to accumulate a previously unidentified intermediate in ubiquinone biosynthesis when grown in the presence of p-hydroxy[7-14C]- or -[u-14C]benzoic acid. This intermediate was isolated from the lipid extracts of a 100-L culture of 26H and purified by various chromatographic procedures to yield 20 mg of product. Analysis by means of NMR, IR, UV, and mass spectrometry revealed the structure of this new intermediate to be 3-methoxy-4-hydroxy-5-hexaprenylbenzoic acid (3-MHHB). In vitro experiments with isolated yeast and rat mitochondria showed that 3-MHHB could be converted to ubiquinone-6. These findings indicate that 3-O-methylation precedes decarboxylation of the prenylated protocatechuic acid intermediate in the biosynthesis of ubiquinone in eukaryotes.