ABSTRACT
Aging represents a multifactorial process involving progressive decline of ener getic capabilities of the organism. Eukaryotic cells include two systems for the synthesis of chemical energy in the form of ATP: (1) the glycolytic system which is independent of oxygen and leads in its absence to the production of lactic acid, and (2) the oxidative phosphorylation system (OXPHOS), located in the inner mitochondrial membrane, and essentially dependent on oxygen. More than 90% of cellular ATP is synthesized in mitochondria by OXPHOS. During evolution nature has preserved a nuclear independent genome in mitochondria, the genetic remnant of an aerobic bacterium which, according to the endosymbiotic hypothe sis (1) fused with an obligate anaerobic cell resulting in the eucaryotic cell. Dur ing evolution most of the genetic content of the aerobic cell has been transfered to the nucleus of the eukaryotic cell. The mitochondrial DNA (mtDNA) contains only 13 structural genes, all of which code for protein subunits of proton pumps, the energy converting enzyme complexes of OXPHOS. Surprisingly, eukaryotic cells can grow and multiply in the absence of mtDNA (2,3). Thus OXPHOS is not required for basic cellular life, but is essential for highly-energy-consuming functions of specialized cells in, for example, the heart, skeletal muscle, and brain.
