Thiyl radical attack on polyunsaturated fatty acids: A possible route to lipid peroxidation

Absolute rate constants have been measured for the reaction of cysteinyl free radicals, CysS •, with linoleic (18:2), linolenic (18:3) and arachidonic acid (20:4) in water/alcohol mixtures using the radiation chemical technique of pulse radiolysis. They are in the order of 10 6 – 10 7 M −1 s −1 and increase with the number of biallylic functions, and with the polarity of the solvent. The reaction is shown to be a hydrogen atom abstraction from biallylic C-H bonds and yields pentadienyl radicals. The thiol mediated repair of the latter is considerably slower. Thiyl free radicals must consequently be considered as a potential source of lipid peroxidation.