Teaching the fundamentals of electron transfer reactions in mitochondria and the production and detection of reactive oxygen species

Mitochondria fulfill a number of biological functions which inherently depend on ATP and O-2(-center dot)/H2O2 production. Both ATP and O-2(-center dot)/H2O2 are generated by electron transfer reactions. ATP is the product of oxidative phosphorylation whereas 02-' is generated by singlet electron reduction of di-oxygen (O-2). O-2(-center dot) then rapidly dismutated by superoxide dismutase (SOD) producing H2O2. O-2(-center dot)/H2O2 were once viewed as unfortunately by-products of aerobic respiration. This characterization is fitting considering over production of O-2(-center dot)/H2O2 by mitochondria is associated with range of pathological conditions and aging. However, O-2(-center dot)/H2O2 are only dangerous in large quantities. If produced in a controlled fashion and maintained at a low concentration, cells can benefit greatly from the redox properties of O-2(-center dot)/H2O2. Indeed, low rates of O-2(-center dot)/H2O2 production are required for intrinsic mitochondrial signaling (e.g, modulation of mitochondrial processes) and communication with the rest of the cell. O-2(-center dot)/H2O2 levels are kept in check by anti-oxidant defense systems that sequester O-2(-center dot)/H2O2 with extreme efficiency. Given the importance of O-2(-center dot)/H2O2 in cellular function, it is imperative to consider how mitochondria produce O-2(-center dot)/H2O2 and how O-2(-center dot)/H2O2 genesis is regulated in conjunction with fluctuations in nutritional and reclox states. Here, l discuss the fundamentals of electron transfer reactions in mitochondria and emerging knowledge on the 11 potential sources of mitochondrial O-2(-center dot)/H2O2 in tandem with their significance in contributing to overall O-2(-center dot)/H2O2 emission in health and disease. The potential for classifying these different sites in isopotential groups, which is essentially defined by the redox properties of electron donator involved in O-2(-center dot)/H2O2 production, as originally suggested by Brand and colleagues is also surveyed in detail. In addition, redox signaling mechanisms that control O-2(-center dot)/H2O2 genesis from these sites are discussed. Finally, the current methodologies utilized for measuring O-2(-center dot)/H2O2 in isolated mitochondria, cell culture and in vivo are reviewed. (C) 2015 The Author. Published by Elsevier B.V.