A mechanism for accelerated degradation of intracellular proteins after limited damage by free radicals.

I propose that limited free radical attack upon proteins, occurring continuously in cells, creates new N-termini (notably aspartate and glutamate) which render the proteins more susceptible to proteolysis by the ubiquitin conjugation system. I suggest that these reactions are a significant part of the previously described 'N-end' and 'PEST' rules, which indicate amino acid termini or sequences which tend to dictate short protein half-lives. I also argue that the N-end rule may apply to sequestered intracellular sites, such as mitochondria, these also being sites of radical generation.