The lipid composition of flight muscle mitochondria isolated from the blowfly, Phormia regina

The microviscosity of liver plasma membranes of rats fed with oleoylanilide

Oleoylanilide was administered orally to groups of rats according to different patterns. Oleoylanilide was perfused at different concentrations through rat liver. Oleoylanilide was added to isolated hepatocytes. Oleoylanilide was added to plasma-membrane preparations. Membrane preparations were obtained after experiments performed in vivo and perfusion experiments and, by using 1,6-diphenylhexa-1,3,5-triene as fluorescence probe, the fluorescence polarization parameter was measured, from which the microviscosity (eta) was calculated. In all cases the microviscosity decreased markedly. Addition of oleoylanilide to hepatocyte preparations and to isolated membranes produced the same effect, increasing the fluidity of the membranes. These data suggest that oleoylanilide partitions into the membrane, disordering some lipid interactions.

Role of proteins and lipids in non-linear Arrhenius plots of Drosophila mitochondrial succinate-cytochrome c reductase studied by rebinding experiments

Abrupt changes in the Arrhenius activation energy of membrane-bound enzymes have often been correlated with changes in the physical state of membrane phospholipids. Similar changes in activation energy have also been found in soluble enzymes. The possibility exists, therefore, that in some of the membrane-bound enzymes the changes might reflect intrinsic changes of the proteins independent of changes in the membrane phospholipids. This hypothesis was investigated using Drosophila mitochondria isolated from wild type and the mutant Ocd ts-1. In this mutant it has been shown that succinate-cytochrome c reductase exhibits a change in Arrhenius activation energy at 18 degrees C which is not found in the wild type (Sondergaard, L., Nielsen, N.C. and Smillie, R.M. (1975) FEBS lett. 50, 126-129). A quantitative thin-layer chromatographic analysis of mitochondrial phospholipids showed sphingomyelin to be more abundant in the wild type than in the mutant (5.2% and 4.3% of the total phospholipids, respectively). Since it was shown that the succinate-cytochrome c reductase had a lipid requirement for full activity, reciprocal rebinding experiments were done. These experiments showed that the reconstituted membranes exhibited the change in activation energy at 18 degrees C only when the protein moiety came from mutant mitochondria, that is, the change was independent of the source of the phospholipids used.