Aggregation of adult and fetal hemoglobin by ingested nitrate anions

The ingested nitrates sourced from tap water, food, chemicals and pharmaceuticals are converted to nitrites in the body surfaces by bacteria and then, the nitrite ions can lead the structural changing in hemoglobin. In the present work, aggregation of the purified hemoglobin in adult (HbA) and in fetus or newborn (HbF) in the presence of nitrite ions were studied. Hemoglobin aggregation was performed chemically in the presence of 10 mg/l nitrite ions and examined by UV-Vis spectrophotometer at 360 nm wavelength. The extrinsic fluorimetric measurements indicated that repulsive electrostatic interaction between nitrite anions and negative charged groups of both types of HbA and HbF molecules leads to expose the hydrophobic patch of the protein molecules. Moreover, the α-helix to β-strand transition in both types of hemoglobins shown by circular dichroism support aggregation process among this protein. However, at natural pH, the protonated amino group of Gly in HbF tends to bind to nitrite anions more than the unprotonated forms of Val residue in HbA. The drastic slop of aggregation plot and shorter lag time of HbF relative to HbA demonstrated more aggregation of former protein.