Nitration Reactions of Proteins in Urban Air: O3 and NO2 Concentrations, Exposure Time, and Implications
RACHEL L. DAVEY, Erick Mattson, J. Alex Huffman,
University of Denver Abstract Number: 451
Working Group: Aerosol Chemistry
AbstractExposure of proteins to atmospheric oxidants like ozone (O
3) and nitrogen dioxide (NO
2) can induce chemical modification, like the formation of nitrotyrosine (NTyr). Proteins with these modifications have been shown to promote adverse human health effects, such as exacerbation of allergies and respiratory disease. Pollen can rupture upon exposure to air pollutants or humidity, releasing cytoplasmic material like allergenic proteins into the atmosphere. These proteins could then undergo heterogenous reactions with pollutants to produce chemically modified proteins, which then can negatively impact human health. To investigate the protein modification process under ambient reaction conditions, bovine serum albumin (BSA), as an inexpensive protein model, and ragweed pollen protein (Amb) were exposed to urban air at two sites in Denver, Colorado for varying lengths of exposure time over the course of two years. NTyr formation in BSA, measured as nitration degree (ND) using high-performance liquid chromatography, was correlated with O
3 and NO
2 concentrations, as well as relative humidity, temperature, and exposure time. Previous laboratory experiments observed ND values of BSA as high as 12%, based on the number of exposed tyrosine residues. The urban site with higher NO
2 and lower O
3 concentrations (<30 and 50 ppb) resulted in ND values between 0-5%, whereas the suburban site with lower NO
2 and higher O
3 concentrations (<20 and 70 ppb) generally resulted in even higher ND values, up to 9%. These observations are consistent with the mechanism proposed via laboratory experiments but had not been shown using ambient exposure. Insight learned from this study has implications for other aerosol chemical mechanisms, such as reactions with other proteins, free amino acids, and polycyclic aromatic hydrocarbons that are subject to chemical reactions in the atmosphere, as well as potentially to indoor environments that produce NO
2.