The function of menaquinone (vitamin K 2) in Escherichia coli K-12

Abstract

1. 1. A gene concerned with the biosynthesis of menaquinone (vitamin K 2) has been mapped by cotransduction at about minute 78 on the Escherichia coli genome. 2. 2. Strains deficient in menaquinone, and in both menaquinone and ubiquinone, were prepared by cotransduction and compared with the parent strain in a study of menaquinone function. 3. 3. No difference was found in the aerobic metabolism of strains with or without menaquinone. 4. 4. The menaquinone-deficient strain grew slowly anaerobically on glucose while the strain deficient in both menaquinone and ubiquinone did not grow at all under these conditions. The inclusion of uracil in the medium restored the growth of the mutant strains to normal. 5. 5. The oxidation of dihydroorotate by anaerobically grown cells of the quinonedeficient strain was examined and menaquinone was found to be required for the anaerobicf oxidation of dihydroorotate to orotate with fumarate as hydrogen acceptor. 6. 6. A fluorimetric test was developed for observing the reduction of menaquinone in membranes and it was shown that dihydroorotate reduced menaquinone which, in turn, was re-oxidised by fumarate. 7. 7. It is concluded that, during anaerobic growth of E. coli, menaquinone is required for one of the reactions of pyrimidine biosynthesis, namely the oxidation of dihydroorotate to orotate with fumarate as hydrogen acceptor and that ubiquinone can partially replace menaquinone in mutants lacking the latter quinone.