Endogenous free radical generation may influence proteolysis in mitochondria.

Isolated Mitochondria were allowed to incorporate radioactive amino acids into protein and proteolysis was then measured. In State 4 free radical generation was manipulated by means of respiratory chain blockers and uncouplers. Conditions of enhanced radical flux resulted in accelerated protein breakdown. We suggest that radicals influence proteolysis in cells both directly (by fragmenting proteins) and indirectly (by rendering proteins more susceptible to proteinases).