Redox properties of the oxygen-detoxifying flavodiiron protein from the human parasite Giardia intestinalis

Arch Biochem Biophys. 2009 Aug 1;488(1):9-13. doi: 10.1016/ Epub 2009 Jun 21.


Flavodiiron proteins (FDPs) are enzymes identified in prokaryotes and a few pathogenic protozoa, which protect microorganisms by reducing O(2) to H(2)O and/or NO to N(2)O. Unlike most prokaryotic FDPs, the protozoan enzymes from the human pathogens Giardia intestinalis and Trichomonas vaginalis are selective towards O(2). UV/vis and EPR spectroscopy showed that, differently from the NO-consuming bacterial FDPs, the Giardia FDP contains an FMN with reduction potentials for the formation of the single and the two-electron reduced forms very close to each other (E(1)=-66+/-15mV and E(2)=-83+/-15mV), a condition favoring destabilization of the semiquinone radical. Giardia FDP contains also a non-heme diiron site with significantly up-shifted reduction potentials (E(1)=+163+/-20mV and E(2)=+2+/-20mV). These properties are common to the Trichomonas hydrogenosomal FDP, and likely reflect yet undetermined subtle structural differences in the protozoan FDPs, accounting for their marked O(2) specificity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Absorption
  • Animals
  • Coenzymes / metabolism
  • Electron Spin Resonance Spectroscopy
  • Flavin Mononucleotide / metabolism
  • Giardia lamblia / enzymology*
  • Humans
  • Iron / metabolism*
  • Oxidation-Reduction
  • Oxygen / isolation & purification
  • Oxygen / metabolism*
  • Parasites / enzymology
  • Protozoan Proteins / metabolism*
  • Substrate Specificity
  • Titrimetry


  • Coenzymes
  • Protozoan Proteins
  • Flavin Mononucleotide
  • Iron
  • Oxygen