Flavodoxin-dependent pyruvate oxidation, acetate production and metronidazole reduction by Helicobacter pylori

Helicobacter pylori flavodoxin was purified to homogeneity from cell extracts of strain NCTC 11637. The molecular weight of the protein was estimated by gel electrophoresis to be 18 kDa. Oxidized flavodoxin showed an absorption spectrum with maxima at 378 nm and 453 nm, and it was reduced to a neutral form of flavin semiquinone by the electrons generated in the oxidation of pyruvate. This coenzyme A dependent pyruvate:flavodoxin oxidoreductase activity of H. pylori was also detected as a reduction of methyl viologen or cytochrome c by bacterial extracts. The apparent Km of pyruvate was 310 microM. Anaerobically incubated bacteria (10[9]) of strain NCTC 11637 produced acetate (96 +/- 16 nmol/h) from pyruvate concomitantly reducing metronidazole (17 +/- 5 nmol/h). In anaerobic conditions both sensitive and resistant H. pylori strains reduced metronidazole, and there was a significant positive correlation between acetate production and metronidazole activation (r = 0.77, P < 0.01, n = 11). In the presence of atmospheric oxygen, H. pylori excreted twice as much acetate but metronidazole was not activated. These results suggest that the pyruvate:flavodoxin oxidoreductase complex catalyses pyruvate oxidation in H. pylori. Electrons generated in this reaction are transferred to flavodoxin and under anaerobic conditions further to metronidazole (imidazoles) thus reducing the drug to its bactericidal form.