The activation of mitochondrial particulate ATPase by liposomes of diacylphospholipids.

1. 1. The stimulation of mitochondrial particulate ATPase by natural phosphatidylcholines was studied in a phospholipid-free preparation from bovine heart obtained by extraction with cholate. The low stimulatory activity of these phospholipids was increased by: (a) introduction of negatively charged amphiphatic substances into the zwitterionic liposomes; (b) addition of Cl- to the incubation medium. 2. 2. Liposomes of acidic phospholipids or phosphatidylcholine containing anionic amphipaths prevented the ATP plus Mg2+-induced decrease of ATPase activity in Mg-ATP particles which have a high content of ATPase inhibitor. 3. 3. Acidic phospholipids, in contrast to phosphatidylcholine, prevented the inhibition of soluble and particulate ATPase by purified ATPase inhibitor. 4. 4. It is concluded that the structure of the lipid-water interface is of primary importance in the stimulation produced by liposomes of diacylphospholipids on particulate mitochondrial ATPase. This effect is associated with the removal of inhibition induced by endogenous ATPase inhibitor on phospholipid-depleted preparations. © 1974.