Flavohemoglobin and nitric oxide detoxification in the human protozoan parasite Giardia intestinalis

Daniela Mastronicola, Fabrizio Testa, Elena Forte, Eugenio Bordi, Leopoldo Paolo Pucillo, Paolo Sarti, Alessandro Giuffrè

Research output: Contribution to journalArticlepeer-review


Flavohemoglobins (flavoHbs), commonly found in bacteria and fungi, afford protection from nitrosative stress by degrading nitric oxide (NO) to nitrate. Giardia intestinalis, a microaerophilic parasite causing one of the most common intestinal human infectious diseases worldwide, is the only pathogenic protozoon as yet identified coding for a flavoHb. By NO amperometry we show that, in the presence of NADH, the recombinant Giardia flavoHb metabolizes NO with high efficacy under aerobic conditions (TN=116±10s-1 at 1μM NO, T=37°C). The activity is [O2]-dependent and characterized by an apparent KM,O2=22±7μM. Immunoblotting analysis shows that the protein is expressed at low levels in the vegetative trophozoites of Giardia; accordingly, these cells aerobically metabolize NO with low efficacy. Interestingly, in response to nitrosative stress (24-h incubation with ≥5mM nitrite) flavoHb expression is enhanced and the trophozoites thereby become able to metabolize NO efficiently, the activity being sensitive to both cyanide and carbon monoxide. The NO-donors S-nitrosoglutathione (GSNO) and DETA-NONOate mimicked the effect of nitrite on flavoHb expression. We propose that physiologically flavoHb contributes to NO detoxification in G. intestinalis.

Original languageEnglish
Pages (from-to)654-658
Number of pages5
JournalBiochemical and Biophysical Research Communications
Issue number4
Publication statusPublished - Sep 2010


  • Anaerobic protozoa
  • Flavin
  • Hemeprotein
  • Nitrosative stress
  • NO amperometry

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Cell Biology
  • Molecular Biology
  • Medicine(all)


Dive into the research topics of 'Flavohemoglobin and nitric oxide detoxification in the human protozoan parasite Giardia intestinalis'. Together they form a unique fingerprint.

Cite this