Keto-acid oxidoreductases in the anaerobic protozoa

In anaerobes, decarboxylation of pyruvate is executed by the enzyme pyruvat e:ferredoxin oxidoreductase, which donates electrons to ferredoxin. The pyr uvate:ferredoxin oxidoreductase and its homologues utilise many alternative substrates in bacterial anaerobes. The pyruvate:ferredoxin oxidoreductase from anaerobic protozoa, such as Giardia duodenalis, Trichomonas vaginalis, and Entamoeba histolytica have retained this diversity in usage of alterna tive keto acids for energy production utilising a wide variety of substrate s. In addition to this flexibility, both T. vaginalis and G. duodenalis hav e alternative enzymes that are active in metronidazole-resistant parasites and that do not necessarily involve donation of electrons to characterized ferredoxins. Giardia duodenalis has two oxoacid oxidoreductases, including pyruvate:ferredoxin oxidoreductase and T. vaginalis has at least three. The se alternative oxoacid oxidoreductases apparently do not share homology wit h the characterized pyruvate:ferredoxin oxidoreductase in either organism. Independently, both G. duodenalis and T. vaginalis have retained alternativ e oxoacid oxidoreductase activities that are clearly important for the surv ival of these parasitic protists.