Alternative 2-keto acid oxidoreductase activities in Trichomonas vaginalis

We have induced high levels of resistance to metronidazole (1 mM or 170 mu g ml(-1)) in two different strains of Trichomonas vaginalis (BRIS/92/STDL/F 1623 and BRIS/92/STDL/B7708) and have used one strain to identify two alter native T. vaginalis 2-keto acid oxidoreductases (KOR) both of which are dis tinct from the already characterised pyruvate:ferredoxin oxidoreductase (PF OR). Unlike the characterised PFOR which is severely down-regulated in metr onidazole-resistant parasites, both of the alternative KORs are fully activ e in metronidazole-resistant T. vaginalis. The first, KOR1, localized in al l membrane fractions but predominantly in the hydrogenosome fraction, is so luble in Triton X-100 and the second, KOR2, is extractable in 1 M acetate f rom membrane fractions of metronidazole-resistant parasites. PFOR and both KOR1 and KOR2 use a broad range of 2-keto acids as substrates (pyruvate, al pha-ketobutyrate, alpha-ketomalonate), including the deaminated forms of ar omatic amino acids (indolepyruvate and phenylpyruvate). However, unlike PFO R neither KOR1 or KOR2 was able to use alpha-ketoglutarate. Deaminated form s of branched chain amino acids (alpha-ketoisovalerate) were not substrates for T. vaginalis KORs. Since KOR1 and KOR2 do not apparently donate electr ons to ferredoxin, and are not down-regulated in metronidazole-resistant pa rasites, we propose that KOR1 and KOR2 provide metronidazole-resistant para sites with an alternative energy production pathway(s) which circumvents me tronidazole activation. (C) 1999 Published by Elsevier Science B.V. All rig hts reserved.