Oxidation of biologic molecules by ozone: the effect of pH.
Ozone (O3) is a powerfully oxidizing pollutant gas. Its toxic effects to animals appear to be worsened by coexposures to acid-generating compounds such as oxides of nitrogen and sulfur. Ozone (16 ppm) oxidizes ascorbic acid and uric acid (two important antioxidants in lung lining fluids) at equal rates at pH 5.0 or pH 7.4. Loss of intrinsic fluorescence and formation of carbonyls in albumin exposed to O3 are similar at both pH values. However, albumin-SH groups are lost much faster on exposure to O3 at pH 7.4 than at acidic pH values. A similar slower rate of -SH group disappearance at acidic pH is seen when cysteine or reduced glutathione are exposed to O3. We suggest that the ability of reduced glutathione, albumin, and other proteins containing -SH groups to scavenge O3 in the respiratory tract is impaired at low pH and that this effect could contribute to the aggravation of O3 toxicity.