Hydrogenosomal ferredoxin of the anaerobic protozoon, Tritrichomonas foetus

A low molecular weight iron-sulfur protein has been purified from Tritrichomonas foetus by deoxycholate extraction of whole cells, ion exchange chromatography, and gel filtration. The purified protein was essentially homogeneous as judged by isoelectric focusing, polyacrylamide gel electrophoresis, and gel filtration. A pI of 4.3 was observed. The molecular weight of the protein was estimated to be 12,000. Chemical and spectral analysis showed the protein to have a [2Fe-2S] cluster. The absorbance spectrum of the oxidized protein showed maxima at 280, 340, 458 and shoulders at 410 and 550 nm. The maximum observed A458/A280 ratio was 0.82 and the absorbance of the oxidized protein at 458 nm was 8,000 M-1 X cm-1. The low temperature EPR spectrum of the protein reduced with dithionite revealed axial symmetry with features at g values of g = 1.94 and g = 2.02. The oxidized protein gave no EPR signal in the g = 1.8 to 2.2 range. Cell fractionation studies indicated the localization of this protein in the hydrogenosome. The protein was able to function as an electron transport component in the reduction of metronidazole (a 5-nitroimidazole derivative) by pyruvate:ferredoxin oxidoreductase and hydrogenase from T. foetus and also from Trichomonas vaginalis and Clostridium pasteurianum as well as in the reduction of cytochrome c by plant NADPH:ferredoxin oxidoreductase. This protein has the characteristics of a ferredoxin and is likely to be a physiological electron carrier in hydrogenosomal pyruvate oxidation.