[Comparative study of lipid transfer between cell organelles using lipid-transfer proteins in vitro].

The transfer of de novo synthesized lipids from microsomes to lipid non-synthesizing membranes was studied in vivo and in vitro from the ratios of specific radioactivities of [14C]cholesterol, [14C] and [32P]phosphatidylcholine and [32P]phosphatidylethanolamine in the nuclei and mitochondria to that in microsomes. The radioactivity of lipids transferred from microsomes to mitochondria and nuclei was identical both in vitro and in vivo and when the lipid-exchange protein of the 105 000 g supernatant was used. Acceleration of lipid metabolism in the liver of gamma-irradiated rats was concomitant with the increase in the rate of labeled cholesterol transfer cation to liver cell nuclei and mitochondria, but remained unchanged in in vitro studies involving lipid-exchange protein. The reduction of phosphatidylethanolamine transfer to the nuclei in vitro and in vivo diminished in the same way. The existence in the cell of mechanisms of transfer of de novo synthesized cholesterol other than lipid-exchange protein is postulated.