Ubiquinone biosynthesis in Escherichia coli K-12. Accumulation of an octaprenol, farnesylfarnesylgeraniol, by a multiple aromatic auxotroph

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Abstract
Cell extracts of a multiple aromatic auxotroph of Escherichia coli K-12, strain AB2830, grown in the absence of precursors of the quinone rings of the ubiquinone and menaquinone molecules, converted 4-hydroxy[U-14C]benzoate into a mixture of 3-octaprenyl-4-hydroxybenzoate and 2-octaprenylphenol. An octaprenol, farnesylfarnesylgeraniol, was isolated from such cell extracts and characterized by n.m.r. and mass spectroscopy. Neither the octaprenol, nor polyprenylation of 4-hydroxy[U-14C]benzoate, could be detected in cell extracts of strain AB2830 grown in the presence of 0.1mm-4-hydroxybenzoate. It was concluded that, in the biosynthesis of ubiquinone, the polyprenyl side chain is added to 4-hydroxybenzoate as a C40 unit, the active form of which is converted by cell extracts into farnesylfarnesylgeraniol. The multiple aromatic auxotroph, when grown in the absence of 4-hydroxybenzoate but in the presence of 4-aminobenzoate, converted the latter compound into 3-octaprenyl-4-aminobenzoate. This compound was isolated from whole cells and characterized by n.m.r. and mass spectroscopy.