INTERACTIONS OF BLOOD METALLOPROTEINS WITH NITROGEN-OXIDES AND OXIDANT AIR-POLLUTANTS

The effects of in vitro exposure of fresh blood and in vivo exposure of animals to atmospheres containing NO, NO2, or O3 were examined on the iron- and copper-containing proteins in whole blood by low-temperature EPR spectroscopy. Exposure of whole blood to NO under conditions in which neither free nor bound O2 is present results in the quantitative conversion of Hb to the Hb-NO derivative. Subsequent exposure of the derivative to air converts nearly all of the Hb-NO to methemoglobin in the reaction whose mechanism is detailed in this report. Nitrite seems to participate only in the terminal stages. In vivo exposure of animals to air containing a few parts per million NO or NO2 gives rise to significant accumulations of both Hb-NO and methemoglobin, the latter being the major product. This effect can be seen under typical ambient conditions. Exposure to NO2, either aerobically or anaerobically, gives rise to a mixture of Hb-NO and methemoglobin in the ratio which ranges between 1:4 and 1:20. Methemoglobin is invariably the major product. Exposure to O3, on the other hand, fails detectably to alter the state of hemoglobin in whole blood, nor does O3 generate a measurable change in organic free radicals. All three gases - NO, NO2, and O3 - significantly increase the signal due to high-spin ( S ̄ = 5 2) ferric catalase, while NO, NO2, and O3 all depress the level of iron transferrin. These effects translate into decreased activity for both proteins. Other metalloproteins in blood which are observable by EPR spectroscopy are, for the most part, insensitive to NO, NO2, or O3. The implications of these chemical changes in terms of health effects of NOx and oxidant air pollution are discussed. © 1979.