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Biochem Biophys Res Commun. 2010 Sep 3;399(4):654-8. doi: 10.1016/j.bbrc.2010.07.137. Epub 2010 Aug 5.

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

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  • 1Department of Biochemical Sciences, CNR Institute of Molecular Biology and Pathology and Istituto Pasteur - Fondazione Cenci Bolognetti, Sapienza University of Rome, I-00185 Rome, Italy.


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 1microM NO, T=37 degrees C). The activity is [O(2)]-dependent and characterized by an apparent K(M,O2)=22+/-7microM. 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.

Copyright 2010 Elsevier Inc. All rights reserved.

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