Analysis of the Respiratory Activity in the Antarctic Yeast M94C9 Reveals the Presence of Respiratory Supercomplexes and Alternative Elements.

The respiratory activities of mitochondrial complexes I, II, and IV were analyzed in permeabilized cells and isolated mitochondria, and the kinetic parameters K and V were obtained. No difference in substrate affinities were found between mitochondria and permeabilized cells. The activities of the components of the mitochondrial respiratory chain of the Antarctic yeast were identified by in-gel activity and SDS-PAGE. The mitochondria exhibited activity for the classical components of the electron transport chain (Complexes I, II, III, and IV), and supercomplexes were formed by a combination of the respiratory complexes I, III, and IV. Unfortunately, the activities of the monomeric and dimeric forms of the F1F0-ATP synthase were not revealed by the in-gel assay, but the two forms of the ATP synthase were visualized in the SDS-PAGE. Furthermore, two alternative pathways for the oxidation of cytosolic NADH were identified: the alternative NADH dehydrogenase and the glycerol-3-phosphate dehydrogenase. In addition, an NADPH dehydrogenase and a lactate cytochrome b2 dehydrogenase were found. The residual respiratory activity following cyanide addition suggests the presence of an alternative oxidase in cells.