Abstract
Physicochemical properties of rat liver mitochondrial membranes have been studied using differential scanning calorimetry (DSC). Exothermic and endothermic lipid phase transition temperatures of mitochondria were detected at -10.5°C and -4.6°C, respectively. Lipid phase transition temperatures of the outer and inner membrane fractions were almost the same although their membrane compositions were different from each other. Mitochondrial lipids free from cholesterol have revealed two distinct, broadened peaks suggesting that cholesterol plays a key role in the cooperativity of membrane lipids protecting them from phase separations.
There were practically no differences in lipid phase transition temperatures between intact mitochondria and their extracted lipid fraction. However, fluorimetric analysis of the latter revealed an increase in the membrane fluidity. Effects of Ca2+, freezing-thawing and ethylene glycol on the physicochemical properties of mitochondrial membranes were also investigated.
The present results suggest that DSC is a useful tool for the study of physicochemical properties of the mitochondrial membranes, but analysis of the data obtained by DSC should be made in the light of those obtained by other methods such as fluorimetry, ESR and NMR.
