Kd. Chapman et al., METABOLISM OF COTTONSEED MICROSOMAL N-ACYLPHOSPHATIDYLETHANOLAMINE, Archives of biochemistry and biophysics, 318(2), 1995, pp. 401-407
N-acylphosphatidylethanolamine (NAPE) was recently shown to be synthes
ized in vitro in cottonseed microsomes by the direct N-acylation of ph
osphatidylethanolamine (PE) with unesterified fatty acids (K. D. Chapm
an and T. S. Moore, 1993, Plant Physiol. 102, 761-769), Here we examin
e the relationship of the synthesis and turnover of NAPE in cottonseed
microsomes to the O-acylation of other membrane phospholipids. PE was
N-acylated in a time-dependent manner with [1-C-14]palmitic acid inde
pendent of exogenously supplied ATP, O-Acylation of PE and phosphatidy
lcholine (PC) with [1-(14) C]palmitic acid proceeded only in the prese
nce of ATP, Further radiolabeling experiments with [1-C-14]palmitoylCo
A and phosphatidyl(N-[1-C-14]palmitoyl)ethanolamine indicated that O-a
cylation of phospholipids occurred via an acylCoA intermediate and not
via an NAPE intermediate, [1-C-14]palmitic acid was released from PC[
1-C-14-dipalmitoyl] in cottonseed microsomes in a Ca2+-dependent manne
r and this [C-14]-FFA was incorporated into [C-14]NAPE in a linear fas
hion. Cottonseed NAPE was selectively hydrolyzed to N-acylethanolamine
(NAE) and N-acyl lysophosphatidylethanolamine (NAlysoPE) by Ca2+-inde
pendent, membrane-bound phospholipase D and A activities, respectively
. NAlysoPE was not hydrolyzed to NAE, indicating that the phospholipas
e D that was active to ward NAPE did not recognize NAlysoPE; instead N
AlysoPE was converted to NAPE in the presence of Ca2+ Collectively, ou
r results indicate that NAPE synthesis and the O-acylation of other ph
ospholipids occur by two separate pathways and that microsomal NAPE is
selectively turned over by membrane-bound phospholipase activities. A
pathway for the metabolism of cottonseed NAPE is outlined. (C) 1995 A
cademic Press, Inc.