Echanges de lipides entre mitochondries, microsomes et surnageant cytoplasmique de cellules de pomme de terre ou de chou‐fleur

Publisher Website
Google Scholar
Abstract
The incorporation rates of [1‐14C]acetate in vivo into the lipids of different subcellular fractions of potato or cauliflower tissues are consistent with a flow of radioactive lipids from microsomes to mitochondria.When potato tuber microsomes, containing phospholipids labelled from [1‐14C]acetate, [32P]‐phosphate or [1‐14C]glycerol, are incubated in vitro with unlabelled mitochondria and cytoplasmic supernatant, the radioactivity of the microsomes decreases strongly within 2 hours; the lipids of the mitochondria and those of the supernatant become radioactive, taking up to 40% of the initial radioactivity. The same transfer of labelled lipids is observed when one incubates labelled mitochondria with unlabelled microsomes.During these experiments, one can observe a marked decrease of the specific radioactivities of the phospholipids present in the initially labelled fractions. This may be explained by a departure of labelled phospholipids from the radioactive fraction towards the other cellular fraction and by an arrival of unlabelled lipids from the initially unlabelled fraction to the radioactive fraction. The results obtained with three different precursors are roughly similar, suggesting that there is an exchange of entire phospholipidic molecules between the cellular fractions. However, the rates of exchange of the lipids labelled from [1‐14C]acetate are a little higher than those observed with the other precursors thus suggesting an exchange of free fatty acids in addition to the exchange of phospholipids.Phosphatidylcholine and phosphatidylethanolamine represent the most important fraction of the exchanged phospholipids.The cytoplasmic supernatant acts as an intermediate in these exchanges. When a volume of supernatant containing radioactive lipids is incubated with unlabelled mitochondria or unlabelled microsomes, the radioactivity of the supernatant lipids decreases. The lipids of the mitochondrial and microsomal fractions, particularly the phospholipids, become labelled.The results obtained when mixing cauliflower subcellular fractions in vitro are very similar.The same flows of lipid exchanges (in vitro) can be observed between potato mitochondria and cauliflower microsomes, or reciprocally. However, a great part of the lipids liberated by the cellular fraction from one species remains blocked in the cytoplasmic supernatant from the other species, which may indicate that the exchange are limited, in this case, by a specific requirement for certain kinds of lipids for the biogenesis of membranes.