Abstract
The resistance of mitochondrial respiration and enzymatic activity to elevated temperatures differs among species in parallel with differences in their maximal body temperatures. To examine the causes of thermal disruption of mitochondrial respiration, we have measured rates of succinate-supported respiration and activities of the mitochondrial enzymes cytochrome c oxidase, succinic dehydrogenase, and malate dehydrogenase in mitochondria from the hydrothermal vent tube worm Riftia pachyptila and the coastal bivalve Solemya reidi. Intact mitochondria and mitochondrial membrane preparations were incubated for 10 min at temperatures between 0° and 70° C, and function was examined at 20° C (R. pachyptila) or 15° C (S. reidi). Incubation at similar elevated temperatures caused inactivation of respiration and caused the activities of several mitochondrial enzymes to either increase or decrease sharply. Fluorescence polarization measurements using the hydrophobic probe 1,6-diphenyl-1,3,5-hexatriene showed that no sharp changes in membrane fluidity occurred at the temperatures at which respiration and membrane-associated enzymes altered activity. Reducing bulk membrane fluidity by enrichment with saturated phospholipids had no effect on the thermal inactivation of membrane-associated enzymes. However, disruption of membrane hydrophobic interactions with detergents, 1-5 mM deoxycholate or 5-25 mM octyl glucoside, significantly reduced the temperatures at which loss of enzyme activity occurred. We conclude that disruption of hydrophobic interactions between membrane proteins and their closely associated lipids, or between membrane proteins themselves, is at least partially responsible for high temperature-induced loss of mitochondrial function.
Published Version
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