Press Releases
Jun. 21, 2011

Aging proteins

— Formation of allergic substances by air pollution —
  • Manabu Shiraiwa (Max Planck Institute for Chemistry, the University of Tokyo)
  • Ulrich Pöschl (Max Planck Institute for Chemistry)
  • Markus Ammann (Paul Scherrer Institut)
  • Thomas Koop (Bielefeld University)


Everybody knows that protein-rich foods can be kept longer if they are dried. In the dry state, they are less susceptible to biological degradation and decomposition by microorganisms. We now explain for the first time, how humidity affects the chemical aging of proteins by reactive gases and air pollutants such as ozone. Dried protein macromolecules are glassy solids, which can be attacked by atmospheric oxidants only on the surface. With increased humidity, however, the proteins take up water and the phase of proteins changes from glassy into a gel-like state. The wet protein gel contains water-filled pores and channels that ozone and other reactive gases can penetrate through, therefore, proteins are chemically aged not only on the surface but throughout the entire material.

A reaction with ozone and other air pollutants causes a change in the chemical structure and biological function of protein molecules. For example, the reaction between protein and mixtures of ozone and nitrogen oxides, particularly in traffic-related polluted air masses with excessive sunlight in summer (photochemical smog), leads to a strengthening of the allergy-inducing effect of proteins in the pollen or pollen grains. These air pollutants are therefore suspected to be involved in the very strong increase in allergies in developed countries. The new findings lead to a mechanistic and quantitative understanding of the interactions between the biosphere and atmosphere and the effects of organic dust particles on climate and health.

Paper information

Manabu Shiraiwa, Markus Ammann, Thomas Koop and Ulrich Pöschl
“Gas uptake and chemical aging of semi-solid organic aerosol particles”.
Proceedings of the National Academy of Sciences of the United States of America (PNAS).
Published online on 20 June 2011

Figure 1

Figure 1. Fluorescence microscope picture of Birch pollen.

Figure 2

Figure 2. Atmospheric processing of amorphous organic aerosol particles from primary emissions or secondary formation in the atmosphere. The phase state can fluctuate between glassy solid, semisolid and liquid depending on ambient relative humidity and temperature. Depending on phase state and diffusivity, the chemical transformation and aging upon interaction with atmospheric oxidants and other trace gases (small red circles) proceeds differently: relatively slow via surface adsorption and reaction on solid particles or relatively fast via bulk absorption and reaction in liquid particles. Particles are activated as ice nuclei (IN) forming ice crystals or as cloud condensation nuclei (CCN) forming water droplets.