Active oxygen induced protein ubiquitination in Chlamydomonas.

When methylviologen-treated Chlamydomonas cells were exposed to light, the amount of ubiquitinated proteins with molecular masses of 28- and 31-kDa were drastically changed, i.e. the former increased within 20 min illumination, while the latter decreased. Since these changes are completely dependent on illumination and suppressed by adding 3-(3,4-dichlorophenyl)-1,1-dimethylurea, it was concluded that these changes were caused by active oxygen stress. Treating cells with hydrogen peroxide did not cause such changes of ubiquitination, suggesting that the molecular species of active oxygen is a superoxide anion.