During the reaction of oxyhemoglobin (HbO2) with nitrite, the concentration of residual nitrite, nitrate, oxygen, and methemoglobin (Hb+) was determined successively. The results obtained at various pH values indicate the following stoichiometry for the overall reaction: 4HbO2 + 4NO- 2 + → 4Hb+ + 4NO- 3 + O2 + 2H2O (Hb denotes hemoglobin monomer). NO2 - binds with methemoglobin noncooperatively with a binding constant of 340 M-1 at pH 7.4 and 25°C. Thus, the major part of Hb+ produced is aquomethemoglobin, not methemoglobin nitrite, when less than 2 equivalents of nitrite is used for the oxidation.
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