Reduction of nitroimidazole derivatives by hydrogenosomal extracts of Trichomonas vaginalis.

The reduction rate of nitroimidazole derivatives by pyruvate:ferredoxin oxidoreductase activity in ferredoxin depleted hydrogenosomal extracts of Trichomonas vaginalis depended on the one-electron midpoint potential (E7(1)) of 15 compounds out of the 16 tested. The results showed a linear correlation with a positive slope between the logarithm of the rate and the E7(1) in the range from -564 to -260 mV. Addition of T. vaginalis ferredoxin stimulated the reduction. The additional rate (stimulated rate minus basal rate) was proportional to the concentration of ferredoxin and independent of the E7(1) of the compounds. The compound with the most positive E7(1) (-243 mV) was, however, reduced more slowly than expected. These findings indicate that reduction in the presence of ferredoxin is the sum of two processes, i.e. electron transfer directly from pyruvate:ferredoxin oxidoreductase and from reduced ferredoxin generated by pyruvate:ferredoxin oxidoreductase activity. The relative role of ferredoxin in reductive activation of nitroimidazole derivatives is greater for compounds with more negative E7(1) values. This observation correlates with the high selectivity of the more negative 5-nitroimidazoles against anaerobic prokaryotic and eukaryotic microorganisms in which ferredoxin plays an important metabolic role.