Temperature-induced Phase Changes in Mitochondrial Membranes Detected by Spin Labeling

Molecular motion data from a spin-labeled fatty acid presented on Arrhenius graphs allow melting points or phase transitions to be inferred in local domains such as membranes. With use of this technique, mitochondria from a chilling-sensitive plant and a homeothermic animal displayed temperature-dependent phase transitions at approximately 12° and 23°, respectively. These temperatures coincide identically with the temperatures below which chillingsensitive plants (12°) or homeothermic animals (23°) are injured upon exposure. Mitochondria from a chilling-resistant plant and a poikilothermic animal did not display any such phase transitions. These data indicate that some membrane-bound enzymes are sensitive to the physical state of membrane lipids.