Mitochondrial Respiratory Chain Alternative Components Activity During Different Growth Phases in Yarrowia Lipolytica

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Mitochondrial respiratory chain alternative components activity during different growth phases in Yarrowia lipolytica.In Yarrowia lipolytica mitochondria, the respiratory chain is constituted by the classic complexes plus an external NADH dehydrogenase (NDH2e) and an alternative oxidase (AOX). This results in a branched electron flux converging and diverging at the ubiquinone oxido-reduction. The oxidation of external NADH and reduction of oxygen via alternative components (NDH2e-ubiquinone-AOX) does not contribute to the proton-motive force and must be regulated depending on the cell energy requirements. Since more energy production is needed in the logarithmic growth phase, the futile oxidation of NADH may be prevented by electron channelling if either NDH2e or AOX bind to the classic complexes. It was observed that in the logarithmic growth phase NDH2e-derived electrons were specifically directed to the cytochrome complexes. In addition, the presence of respiratory supercomplexes plus the interaction of NDH2e with these complexes were evaluated using different techniques. NDH2e was detected in association with the cytochromic pathway. In contrast, in the stationary growth phase NDH2e-derived electrons were oxidised both, by the alternative and by the cytochromic pathway. This is in agreement with a higher NADH dehydrogenase activity detected in the stationary growth phase in combination with the lower activity of the cytochromic complexes and enhanced AOX. In stationary growth phase NDH2e no longer co-migrates with the cytochrome c oxidase when separated by ion exchange chromatography. The redirection of electrons from the cytochromic to the alternative pathway during the stationary growth phase is probably due to a combination of several factors: i) less amount of respiratory complex IV, to which NDH2e is believed to associate with; ii) higher transmembrane potential reached in the stationary growth phase and; iii) overexpression of NDH2e.