Generation of NO during oxidation of hemoglobin ferroforms by nitrite.

The oxidation of hemoglobin solutions or erythrocyte suspensions containing a mixture of deoxyHb and oxyHb by NaNO2 (under decreased partial pressure of dissolved O2) resulted in the generation of metHb and nitrosoHb. The maximum amount of nitrosoHb was generated during the oxidation of deoxyHb. An increase in oxygen content was accompanied with increased generation of metHb, which was the only hemoglobin form under aerobic conditions. In the presence of oxygen, GSH was oxidized by NaNO2 to GSSG either in solution of oxyHb or in the structure of erythrocytes. GSH decelerated the oxidation of Hb to metHb due to prolongation of the slow phase and suppression of the autocatalytic phase of the reaction. The oxidation of GSH to GSSG was induced by NO2 radicals and not by NO. The incubation of deoxyHb with S-nitrosoglutathione resulted in its complete conversion to nitrosoHb, and this indicated that NO was released during the spontaneous decomposition of GSNO. The addition of S-nitrosoglutathione to oxyHb resulted in the generation of metHb in the solution.