1: Chem Phys Lipids. 2005 Jan;133(1):1-15. 

Modulation of the in vitro activity of lysosomal phospholipase A1 by membrane

Piret J, Schanck A, Delfosse S, Van Bambeke F, Kishore BK, Tulkens PM,
Mingeot-Leclercq MP.

Unite de Pharmacologie Cellulaire et Moleculaire, Universite catholique de
Louvain 73.70, Avenue E. Mounier 73, B-1200 Brussels, Belgium.

Lysosomal phospholipases play a critical role for degradation of cellular
membranes after their lysosomal segregation. We investigated the regulation of
lysosomal phospholipase A1 by cholesterol, phosphatidylethanolamine, and
negatively-charged lipids in correlation with changes of biophysical properties
of the membranes induced by these lipids. Lysosomal phospholipase A1 activity
was determined towards phosphatidylcholine included in liposomes of variable
composition using a whole-soluble lysosomal fraction of rat liver as enzymatic
source. Phospholipase A1 activity was then related to membrane fluidity, lipid
phase organization and membrane potential as determined by fluorescence
depolarization of DPH, (31)P NMR and capillary electrophoresis. Phospholipase A1
activity was markedly enhanced when the amount of negatively-charged lipids
included in the vesicles was increased from 10 to around 30% of total
phospholipids and the intensity of this effect depended on the nature of the
acidic lipids used (ganglioside GM1<phosphatidylinositol approximately
phosphatidylserine approximately phosphatidylglycerol approximately
phosphatidylpropanol<phosphatidic acid). For liposomes containing
phosphatidylinositol, this increase of activity was not modified by the presence
of phosphatidylethanolamine and enhanced by cholesterol only when the
phosphatidylinositol content was lower than 18%. Our results, therefore show
that both the surface-negative charge and the nature of the acidic lipid
included in bilayers modulate the activity of phospholipase A1 towards
phosphatidylcholine, while the change in lipid hydration or in fluidity of
membrane are less critical. These observations may have physiological
implications with respect to the rate of degradation of cellular membranes after
their lysosomal segregation.

PMID: 15589222 [PubMed - in process]