Phospholipase d activity facilitates ca2+-induced aggregation and
fusion of complex liposomes.
Blackwood, R. Alexander, James E. Smolen, Amy Transue, Ronald J.
Hessler, Donna M. Harsh, Ruth C. Brower, and Scott French.
University of Michigan Medical Center, Ann Arbor, Michigan 48109
-0244, Departmaent of Pediatrics, Divisions of Infectious Diseases and
Hematology
APStracts 3:0388C, 1996.
Phospholipase D activation in stimulated neutrophils results in the
conversion of membrane phosphatidylcholine (PC) to phosphatidic acid
(PA). This change in membrane phospholipid composition has two
potentially positive effects on degranulation: 1) it replaces a non
-fusogenic phospholipid with a fusogenic one; and 2) it increases the
potential for interactions between membranes and the annexins.
Modeling neutrophil degranulation, we examined the effect of
phospholipase D (Streptomyces chromofuscus) hydrolysis on the
aggregation and fusion of liposomes in the presence and absence of
annexin I. We found that PLD-mediated conversion of PC to PA lowered
the [Ca2+] required for fusion. Annexin I increased the rate of
fusion in the presence of PA, although it did not lower threshold
[Ca2+], which remained above the physiologic range. However,
following hydrolysis by PLD, annexin I lowered the [Ca2+] required
for aggregation by almost 3 orders of magnitude to near physiologic
concentrations. These studies indicate that the activation of
phospholipase D and the production of PA may play a role in annexin
-mediated membrane-membrane apposition.
Received 5 August 1996; accepted in final form 21 October 1996.
APS Manuscript Number C439-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996