SUMMARY: H production by the human protozoan parasite was monitored continuously under a mobile gas phase using a membrane-inlet mass spectrometer. Simultaneous and continuous measurement of dissolved H, O and CO indicated that H evolution was inhibited at levels of O (<0·25 μmUM) undetectable by the technique, whereas CO production was stimulated. Respiration was not stimulated by admitting H to the gas phase. Metronidazole inhibited both H and CO production. Values of for inhibition of H formation in strain ATCC 30001 (metronidazole sensitive) of 0·16 mM and in strain 85 (metronizadole resistant) of 1·0 mM were obtained. These data suggest that metronidazole not only competes with protons as electron acceptor but that the drug itself or a product of reduction actively inhibits some hydrogenosomal enzyme or electron carrier involved in H production. Under these conditions metronidazole inhibition leads to irreversible loss of cell motility.


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