Respiration of Trichomonas vaginalis Components detected by electron paramagnetic resonance spectroscopy

Abstract

Electron paramagnetic resonance (EPR) spectrometry was used to characterise the iron‐sulphur clusters present in the human parasite, Trichomonas vaginalis, an aerotolerant anaerobic protozoan which lacks mitochondria. From observations of whole cells and subcellular fractions, the majority of the EPR signals are derived from one of the two main terminal respiration sites, the hydrogenosome; fractionation of hydrogenosomes revealed that a large proportion of these signals were associated with the membrane of these organelles. Resolution into eight species was achieved by varying the degree of reduction and the temperature of the samples. One component, a [2Fe–2S] ferredoxin reducible by pyruvate: ferredoxin oxidoreductase, corresponds to that previously purified, and predominates in spectra scanned at temperatures higher than 45 K. This species (mid‐point redox potential – 300 ± 20 mV) was detected both in a hydrogenosomal membrane fraction and in the matrix fraction derived from broken organelles. Another iron‐sulphur species (mid‐point potential – 270 mV) was detectable in both membrane and matrix at temperatures lower than 30 K. Four other reduced species were confined to the hydrogenosomal membrane and a fifth was not detected after subfractionation, although it appeared in intact organelles. This species is assumed to be highly unstable. Free‐radical signals in hydrogenosome‐enriched fractions probably arise from flavoprotein semiquinones; no other signals were obtained from the cytosolic fractions incubated with NADH. A signal in the oxidised state was observed in the hydrogenosomal membrane. Possible identities of hydrogenosomal iron‐sulphur clusters are discussed in relation to previously established enzyme activities. Copyright © 1986, Wiley Blackwell. All rights reserved