Biosynthesis of bacterial menaquinones. Menaquinone mutants of Escherichia coli.

The isolation of six menaquinone mutants of Escherichia coli is described. It was shown that the mutants fall into two genetic classes. The first class carries mutations in a gene designated menA, which was located at minute 78 on the E. coli chromosome by cotransduction with the glpK and metB genes. The second class carries mutations in a gene designated menB. It was shown that this gene was not cotransducible with the menA gene. The biosynthesis of menaquinone in E. coli was studied using a variety of mutants blocked in aromatic biosynthesis together with the two classes of menaquinone mutants. It was demonstrated that chorismate is the branch point compound leading to menaquinone, and that 2-succinylbenzoic acid and 1,4-dihydroxy-2-naphthoic acid can serve as menaquinoone precursors in E. coli. It was also shown that menA- and menB- strains accumulate 1,4-dihydroxy-2-naphthoic acid and 2-succinylbenzoic acid, respectively, in their culture supernatants. The accumulation of the two compounds by the mutants together with their activity as menaquinone precursors provide strong evidence that they ar true intermediates in menaquinone biosynthesis. A pathway is proposed for the biosynthesis of bacterial menaquinones in which each intermediate has been adequately characterized.