Importance of the lon protease in mitochondrial maintenance and the significance of declining lon in aging.

Mitochondria are a major intracellular source of free radicals and related oxidants. It is generally agreed that the mitochondrial production of such reactive oxygen and nitrogen species increases with age. Antioxidant systems in the mitochondria play an important role in limiting the amount of oxidative damage to tolerable levels. The Lon protease degrades oxidatively modified proteins in the mitochondrial matrix, a function similar to that of the 20S proteasome in the cytoplasm. Recently it was shown that inactive aconitase, a preferential substrate for the Lon protease, might be involved in the maintenance of the mitochondrial genome. Lon protease expression and activity declines with age, which may contribute to the accumulation of the oxidatively modified protein aggregates typically observed in aging and diseased cells. In addition, Lon has multiple functions, such as DNA binding and chaperone activity, for the assembly of respiratory complexes in the Electron Transport Chain. Taken together, Lon and aconitase may be key players in the maintenance of mitochondrial homeostasis under conditions of stress, and (partial) compromise of their function may contribute to both aging and degenerative diseases.