Oxidative Stress in Mitochondria

Abstract

Oxygen is necessary for most forms of life. Its reduction to water provides the energy that allows the impressive complexity of higher organisms. However, oxygen reduction is a mixed blessing. Not only does it permit the biosphere’s versatility, but it is also life-threatening. This is because incompletely reduced oxygen species, when uncontrolled, can nonspecifically oxidize, and thereby damage, biological molecules. Oxygen’s nature as a double-edged sword manifests itself best in mitochondria, where most of the oxygen utilized by eukaryotic cells is reduced. This chapter summarizes the sources of oxidative stress in mitochondria, how these organelles cope with it, and the consequences of oxidative stress in mitochondria. Many aspects concerning reactive oxygen and mitochondria have been reviewed previously. Therefore, only some early key references are explicitly cited; others can be found in the quoted reviews. Even the newer literature is not covered comprehensively due to space limitations. Rather, this chapter focuses on some selected topics which in the authors’ opinions are thoroughly investigated or promise to be particularly important in the future. The newly emerging area of the importance of nitric oxide for mitochondria is dealt with more comprehensively. It will be seen that stress for mitochondria, as on a higher level for an individual, has both negative and positive aspects (Richter et al. 1995).

THE MITOCHONDRIAL RESPIRATORY CHAIN
In nucleated cells, mitochondria provide most of the ATP, with the remainder being formed during glycolysis. Mitochondrial ATP is generated by oxidative phosphorylation in a process that uses molecular oxygen as the...