New advances in coenzyme Q biosynthesis

Coenzyme Q (or ubiquinone) is the product of two distinct biosynthetic path ways: the lipid "tail" of coenzyme Q is formed via the isoprene biosyntheti c pathway, and the quinone ring derives from the metabolism of either shiki mic acid or tyrosine. In general, eukaryotic organisms use the classical me valonate pathway to form isopentenyl- and dimethylallyl-diphosphate, the fi ve carbon building blocks of the polyisoprenoid tail, and prokaryotes use 1 -deoxy-D-xylulose-5-phosphate, formed via the Rohmer pathway. The quinone r ing precursor is 4-hydroxybenzoic acid, which is formed directly from chori smate in Saccharomyces cerevisiae and Escherichia coli, or from tyrosine in animal cells. Ring modification steps including prenylation, decarboxylati on, and successive hydroxylation and methylation steps form the fully subst ituted benzoquinone ring of coenzyme Q. Many of the genes and polypeptides involved in coenzyme Q biosynthesis have been isolated and characterized by utilizing strains of E. coli and S. cerevisiae with mutations in the nbi a nd COQ genes, respectively. This article reviews recent progress in charact erizing the biosynthesis of coenzyme Q in E. coli. S. cerevisiae, and other eukaryotic organisms.