Proteins bearing oxidation-induced carbonyl groups are not preferentially ubiquitinated

A substantial part of soluble, oxidized proteins are degraded by the proteasome. However, it is still under debate whether these oxidized proteins are degraded by the 26S proteasome in an ubiquitin-dependent way or in an ubiquitin-independent way by the 20S proteasome. Therefore, we treated cells with H₂O₂ and UV-A irradiation and detected protein carbonyls and ubiquitination by immunoblotting. Separation of ubiquitinated proteins from non-ubiquitinated reveals that most oxidized proteins are not ubiquitinated.