title: Phase transitions in yeast mitochondrial membranes. The effect of temperature on the energies of activation of the respiratory enzymes of Saccharomyces cerevisiae.
abstract: The effect of temperature on the activation energies of mitochondrial enzymes of the yeast Saccharomyces cerevisiae was examined. Non-linear Arrhenius plots with discontinuities in the temperature range 14-19 degrees C and 19-22 degrees C were observed for the respiratory enzymes and mitochondrial ATPase (adenosine triphosphatase) respectively. A straight-line Arrhenius plot was observed for the matrix enzyme, malate dehydrogenase. The activation energies of the enzymes associated with succinate oxidation, namely, succinate oxidase, succinate dehydrogenase and succinate-cytochrome c oxidoreductase, were in the range 60-85kJ/mol above the transition temperature and 90-160kJ/mol below the transition temperature. In contrast, the corresponding enzymes associated with NADH oxidation showed significantly lower activation energies, 20-35kJ/mol above and 40-85kJ/mol below the transition temperature. The discontinuities in the Arrhenius plots were still observed after sonication, treatment with non-ionic detergents or freezing and thawing of the mitochondrial membranes. Discontinuities for cytochrome c oxidase activity were only observed in freshly isolated mitochondria, and no distinct breaks were observed after storage at -20 degrees C. Mitochondrial ATPase activity still showed discontinuities after sonication and freezing and thawing, but a linear plot was observed after treatment with non-ionic detergents. The results indicate that the various enzymes of the respiratory chain are located in a similar lipid macroenvironment within the mitochondrial membrane.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism; D005227:Fatty Acids / Q000032:analysis; D008291:Malate Dehydrogenase / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D010101:Oxygen Consumption; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013384:Succinate Cytochrome c Oxidoreductase / Q000378:metabolism; D013385:Succinate Dehydrogenase / Q000378:metabolism; D013386:Succinates / Q000378:metabolism; D013696:Temperature; D013816:Thermodynamics
chemical_list: D005227:Fatty Acids; D013386:Succinates; D013384:Succinate Cytochrome c Oxidoreductase; D008291:Malate Dehydrogenase; D013385:Succinate Dehydrogenase; D009247:NADH, NADPH Oxidoreductases; D003576:Electron Transport Complex IV; D000251:Adenosine Triphosphatases