The fate of phosphatidylethanolamine formed by decarboxylation in rat brain mitochondria

In the liver, the synthesis and the decarboxylation of phosphatidylserine (PS) are a part of a metabolic cycle forming choline from serine. Yet, in the brain, the methylation of PE to phosphatidylcholine is a minor path. Therefore it is possible that the decarboxylation of PS has different biological meanings in the two organs. In this paper, we follow the formation and the fate of radioactive PE; to this purpose, we load brain mitochondria with PS by incubating cell homogenates with labelled serine in base-exchange conditions. Then, we isolate mitochondria and incubate them for PS decarboxylase. We also subfractionate mitochondria to investigate the distribution of PE in inner and outer membranes. We conclude that newly formed PE slowly moves from its site of synthesis (inner mitochondrial membranes). Besides, it reacts better with TNBS and with FLA than the pre-existing PE. This suggests that the newly-synthesised lipid does not mix quickly with the rest of mitochondrial PE. Therefore, our data demonstrate that the fate of PE formed through the decarboxylation path in the brain is different from that reported for the liver where newly-formed PE is rapidly exported to outer mitochondrial membranes.