The ATP-dependent translocation of phosphatidylserine to the mitochondria is a process that is restricted to the autologous organelle.

The general properties of phosphatidylserine synthesis and translocation to the inner mitochondrial membrane which occur in both intact and permeabilized cells are now shown to occur in cells that are disrupted by shearing. In disrupted cells the synthesis of phosphatidylserine requires ATP and is blocked by preventing Ca2+ sequestration. The translocation of nascent phosphatidylserine to the mitochondria also requires ATP in disrupted cells. Using disrupted cells it is possible to test whether the translocation of nascent phosphatidylserine to the mitochondria is restricted to autologous mitochondrial acceptors or is possible with heterologous mitochondrial acceptors. To examine the nature of the transport process, a donor and acceptor population of cells were prepared. The donor cells were poisoned with hydroxylamine which irreversibly inactivates phosphatidylserine decarboxylase and will prevent the conversion of nascent phosphatidylserine to phosphatidylethanolamine. The acceptor cells were not treated with hydroxylamine so that any phosphatidylserine generated in the donor cell that reached the inner mitochondrial membrane of the acceptor cells would be decarboxylated to form phosphatidylethanolamine. Disrupted donor cells were pulse labeled with [3H]serine for 40 min to permit the synthesis of [3H] phosphatidylserine, and then further incorporation of radiolabel was arrested by chelating Ca2+. When the prelabeled disrupted donor cells were mixed with disrupted acceptor cells the latter failed to decarboxylate the nascent phosphatidylserine. In control experiments the addition of hydroxylamine-poisoned cells did not alter the transfer of nascent phosphatidylserine to autologous mitochondria present in unpoisoned cells. These results indicate that the ATP-dependent translocation of phosphatidylserine to the mitochondria is a process that is restricted to the autologous organelle.