Interaction Between Phospholipids and Adenosine Triphosphatase Inhibitor

Abstract

Liposomes of diacylphospholipids need a negative charge in order to stimulate phospholipid-depleted mitochondria1 particulate ATPase (adenosine triphosphatase) (F. Dabbeni-Sala, R. Furlan, A. Pitotti & A. Bruni, unpublished work). Negative charges can be provided by the polar head of phospholipid forming the liposomes or by introducing anionic amphipaths into isoelectric phospholipid particles. In addition, it was found that zwitterionic liposonies of phosphatidylcholine became active when incubation medium was supplemented with relatively large amounts of some anions, notably C1-. Anions are known to prevent association of soluble ATPase with the ATPase inhibitor (Pullman & Monroy, 1963). Investigations on the stimulation produced by liposomes of acidic phospholipids have shown that a phospholipid-depleted preparation obtained from submitochondrial particles containing low amounts of ATPase inhibitor (AS-particles, Racker & Horstman, 1967) was stimulated without the assistance of C1anions. Conversely, C1anions increased the stimulation of a phospholipid-depleted preparation derived from submitochondria1 particles with a high content of ATPase inhibitor (Mg-ATP particles, Low & Vallin, 1963). Mg-ATP submitochondrial particles with intact phospholipid-content have low ATPase activity owing to the tight association between the ATPase and the inhibitor. The ATPase activity could be further decreased by appropriate incubation with ATP and Mg2+. Under these conditions, low concentrations of diphosphatidylglycerol stimulated the activity. The phospholipid-induced ATPase was sensitive to oligomycin. Acidic phospholipids (but not phosphatidylcholine) prevented the inhibition of ATPase activity induced by the purified ATPase inhibitor on soluble and particulate preparations. Diphosphatidylglycerol was the most active. These results indicated that liposomes of anionic diacylphospholipids can influence the relation between mitochondria] ATPase and ATPase inhibitor decreasing their association. Acidic phospholipids, mainly diphosphatidylglycerol, are known to produce solubilization of oligomycin-insensitive ATPase (Toson et al., 1972).