Biosynthesis of bacterial menaquinones: the membrane-associated 1,4-dihydroxy-2-naphthoate octaprenyltransferase of Escherichia coli.

It has been postulated that 1,4-dihydroxy-2-naphthoic acid is the naphthalenic intermediate in the biosynthesis of menaquinone (vitamin K2) in Escherichia coli to which the octaprenyl side chain is attached to from demethylmenaquinone. In the present work the presence of enzyme, 1,4-dihydroxy-2-naphthoate octaprenyltransferase, which catalyzes the conversion of 1,4-dihydroxy-2-naphthoate to demethylmenaquinone was demonstrated in cell extracts of E. coli. Demethylmenaquinone-9 was formed when the naphthoate was incubated with cell extracts and the synthetic substrate, solanesyl pyrophosphate, in the presence of Triton X-100. Solanesyl monophosphate could not substitute for the pyrophosphate in the reaction. The prenylation of of 1,4-dihydroxy-2-naphthoate was also studied in a strain of E. coli which accumulates octaprenyl pyrophosphate, the natural precursor of the menaquinone side chain. The octaprenyltransferase was shown to be membrane bound and to require magnesium ions for optimal activity. A menA-mutant of E. coli was found to lack the octaprenyltransferase activity, suggesting that the menA gene is the structural gene for this enzyme. However, this strain had normal levels of 4-hydroxybenzoate octaprenyltransferase, the enzyme catalyzing the analogous prenylation reaction in ubiquinone biosynthesis, providing additional evidence that the two octaprenyltransferases are quite distinct.