Ubiquinone biosynthesis in microorganisms

The quinoid nucleus of the benzoquinone. ubiquinone (coenzyme Q; Q). is der ived from the shikimate pathway in bacteria and eukaryotic microorganisms. Ubiquinone is not considered a vitamin since mammals synthesize it from the essential amino acid tyrosine. Escherichia coli and other Gram-negative ba cteria derive the 4-hydroxybenzoate required for the biosynthesis of Q dire ctly from chorismate. The yeast, Saccharomyces cerevisiae, can either form 4-hydroxybenzoate from chorismate or tyrosine. However, unlike mammals, S. cerevisiae synthesizes tyrosine in vivo by the shikimate pathway. While the reactions of the pathway leading from 4-hydroxybenzoate to Q are the same in both organisms the order in which they occur differs. The 4-hydroxybenzo ate undergoes a prenylation, a decarboxylation and three hydroxylations alt ernating with three methylation reactions, resulting in the formation of Q. The methyl groups for the methylation reactions are derived from S-adenosy lmethionine. While the prenyl side chain is formed by the 2-C-methyl-D-eryt hritol 4-phosphate (non-mevalonate) pathway in E. coli, it is formed by the mevalonate pathway in the yeast. (C) 2001 Federation of European Microbiol ogical Societies. Published by Elsevier Science B.V. All rights reserved.