Interactions of blood metalloproteins with nitrogen oxides and oxidant air pollutants

• Published in: Environmental research 1979-10, Vol.20 (1), p.43-65
• Main Authors: Case, George D., Dixon, Jonathan S., Schooley, John C.
• Format: Article
• Language: English
• Subjects: Air Pollutants; Animals; Catalase; Electron Spin Resonance Spectroscopy; Hemoglobins; Humans; Kinetics; Metalloproteins - blood; Mice; Nitrogen Oxides - blood; Ozone; Rabbits; Thermodynamics; Transferrin
• ISSN: 0013-9351; 1096-0953
• DOI: 10.1016/0013-9351(79)90084-7

The effects of in vitro exposure of fresh blood and in vivo exposure of animals to atmospheres containing NO, NO 2, or O 3 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 O 2 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 NO 2 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 NO 2, 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 O 3, on the other hand, fails detectably to alter the state of hemoglobin in whole blood, nor does O 3 generate a measurable change in organic free radicals. All three gases — NO, NO 2, and O 3 — significantly increase the signal due to high-spin ( S ̄ = 5 2 ) ferric catalase, while NO, NO 2, and O 3 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, NO 2, or O 3. The implications of these chemical changes in terms of health effects of NO x and oxidant air pollution are discussed.