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

摘要: 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 only pathogenic protozoon as yet identified coding for flavoHb. By NO amperometry we show that, presence NADH, recombinant flavoHb metabolizes with high efficacy under aerobic conditions (TN=116+/-10s(-1) at 1microM NO, T=37 degrees C). The activity [O(2)]-dependent characterized an apparent K(M,O2)=22+/-7microM. Immunoblotting analysis shows that protein expressed low levels vegetative trophozoites Giardia; accordingly, these cells aerobically metabolize efficacy. Interestingly, response (24-h incubation 5mM nitrite) expression enhanced thereby become able efficiently, being sensitive both cyanide carbon monoxide. NO-donors S-nitrosoglutathione (GSNO) DETA-NONOate mimicked effect nitrite on expression. We propose physiologically contributes detoxification G. intestinalis.