Inhibition of mitochondrial phospholipase A2 by mono- and dilysocardiolipin

Abstract

Phospholipase A2 extracted from the acetone powder of previously frozen rat liver mitochondria is strongly inhibited compared to the activity manifest before acetone powder preparation. Activity is substantially recovered upon partial purification of the enzyme by gel filtration chromatography. Inhibitor activity elutes in the void volume from the column and is obtained in the chloroform layer when void volume fractions are subjected to a Folch extraction. Structural studies support the inhibitor being monolysocardiolipin. Under the assay conditions employed, 1 molecule of the inhibitor per 5000 substrate molecules or 40 nM on a nominal concentration basis is I50 for the mitochondrial enzyme. The agent is similarly effective against pancreatic and snake venom phospholipases A2. Monolysocardiolipin and dilysocardiolipin prepared enzymatically from bovine heart cardiolipin are less potent than the material arising from rat liver cardiolipin by factors of 10- and 30-fold, respectively, yet are still highly potent compared to the other known inhibitors of this enzyme. Differences in acyl group composition, in the degree of acyl group oxidation, or in structural isomerism between the sn-1 and sn-2 positions of the lyso compounds may account for the difference in potency between the materials derived from rat liver and bovine heart.

Membrane lipids and cell death: an overview

“…Indeed, under the conditions inducing a marked conversion of CL into MCL, we did not detect a significant increase in the activity of phospholipases present in isolated mitochondria . This is consistent with the fact that MCL is a powerful inhibitor of mitochondrial PLA2 (Reers and Pfeiffer, 1987), so that its accumulation would block local phospholipases.…”

Pro-apoptotic Bid induces membrane perturbation by inserting selected lysolipids into the bilayer

“…Because of the crucial role of CL in membrane structure and plasticity of mitochondria [55], tBid-mediated alteration of CL homoeostasis would be responsible for the structural and functional changes observed in vitro and in vivo (compare [61]). In particular, tight binding of tBid to MCL would sequester this lipid from other reactions, thus removing it as a product inhibitor of the transacylase process of CL remodelling [47], as well as of mitochondrial PLA2 [62]. Further studies are required to verify the biochemical details of the predicted effects of tBid on mitochondria.…”

Proapoptotic Bid binds to monolysocardiolipin, a new molecular connection between mitochondrial membranes and cell death

“…CL transformation into MCL may not derive from enhanced activity of mitochondrial PLA2, since this activity does not increase within 2 h of Fas-induced apoptosis, and would be potently inhibited by MCL. 37 However, death receptor activation of other phospholipases has been reported 36,38 and could dynamically contribute to the observed changes in mitochondrial lipids. In this respect, it would be interesting to determine whether lysosomal lipases -the enzymes normally responsible for recycling cardiolipin 20 -are either activated or released from the lumen of lysosomes/endosomes and contribute to the degradation of mitochondrial lipids during apoptosis.…”