Further characterization of mitochondrial contact sites: effect of short-chain alcohols on membrane fluidity and activity.

Two mitochondrial contact site-enriched fractions were further characterized by freeze-fracture electron microscopy. Examination of the replicas revealed that these two fractions are in the form of vesicles with membrane sheets attached to the vesicles. The physical state of these fractions has been investigated by means of steady-state fluorescence polarization to assess the effects of alcohols on their fluidity properties and activity. Comparison between intact membranes and their extracted lipids shows that butanol and hexanol induce a differential increase of the overall membrane fluidity in the two contact site-enriched fractions. This alteration in the membrane dynamics leads to a complex modulation of cytochrome c oxidase activity in both fractions. These results bring further evidence for the existence of morphologically and functionally distinct domains in mitochondrial membranes.