Australian researchers have discovered that nitrate radicals irreversibly damage amino acids. This raises the possibility that the radicals play a role in respiratory disease, they claim. 

Nitrogen dioxide and ozone have been linked to airway diseases such as asthma, although their exact role is not clear. In the atmosphere, these gases can react to form extremely reactive nitrate radicals, leading Uta Wille and Duanne Sigmund at the University of Melbourne, Victoria, to question whether there is a link between these radicals and respiratory disease. 

As part of their research, the duo has found that nitrate radicals irreversibly damage aromatic amino acids, forming compounds including -nitrate esters, -carbonyl and aromatic nitro-compounds. 'The reaction forms oxidised products,' explains Wille, 'some of which have been found in polluted air and are associated with immune stimulation.' By analysing these products the researchers proposed a mechanism for the oxidation and nitration reactions.

Nitrate radicals will react with aromatic amino acids. The radicals can form in the atmosphere from nitrogen dioxide and ozone

'The next step is to study the radicals' role in damage to proteins, peptides and carbohydrates - molecules that line the cells of the respiratory tract and so are in direct contact with the atmosphere,' says Wille. Ultimately the team wants to check whether the radicals can migrate through the cell membrane, 'where they could cause damage inside the cell,' Wille adds.

Malcolm Forbes, an expert in free radical chemistry at the University of North Carolina at Chapel Hill, US, welcomes the research, and says: 'The results will have a significant impact on research into oxidative damage to proteins, particularly in regard to respiratory illness. The challenge now is to correlate these results with in vivo studies to assess the real impact to society.'  

Russell Johnson