Electron competition process in respiratory chain: Regulatory mechanisms and physiological functions

In mitochondria isolated from the yeast Saccharomyces cerevisiae, under non-phosphorylating conditions, we have previously shown that there is a right of way for electrons coming from the external NADH dehydrogenase, Nde1p. In this work, we show that the electron competition process is identical under more physiological conditions i.e. oxidative phosphorylation. Such a competition generates a priority for cytosolic NADH reoxidation. Furthermore, this electron competition process is associated with an energy wastage (the “active leak”) that allows an increase in redox equivalent oxidation when the redox pressure increases. When this redox pressure is decreased, i.e. under phosphorylating conditions, most of this energy wastage is alleviated. By studying mutant strains affected either in respiratory chain supramolecular organization or in electron competition activity, we show that the respiratory chain supramolecular organization is not responsible for the electron competition processes. Moreover, we show two distinct relationships between the respiratory rate and the quinone redox state that seem to indicate two quinone pools that are involved in the electron right of way. Indeed, the more reduced pool would be associated to the electron right of way for the external dehydrogenases whereas the less reduced pool would be associated to the electron right of way for the internal dehydrogenases.