The transfer of phosphatidylserine from rat brain microsomes to mitochondria is regulated by microsomal lipid pattern

We label the phosphatidylserine of rat brain microsomes through the base-ex- ". change reaction and study the export of this lipid to mitochondria in a reconstituted system. We fuse microsomes to liposomes to vary the lipid composition of donor membranes and investigate the effect of membrane lipid pattern on phosphatidylserine movement. The specific radioactivity of the phosphatidylserine transferred to mitochondria is higher than that of microsomal phosphatidylserine. This finding supports the hypothesis that the lipid is compartmented in microsomes and that the radioactive, newly synthesized phosphatidylserine is much better exported than the bulk of microsomal phospholipid. The transfer of phosphatidylserine from microsomes, where it forms through the base-exchange reaction, to mitochondria, where it decarboxylates to phosphatidylethanolamine, is enhanced by phosphatidylserine itself, and by other lipid classes. This is proposed as a part of a possible mechanism for regulating phosphatidylserine metabolism in the brain.