Metabolism of cottonseed microsomal N-acylphosphatidylethanolamine.
N-acylphosphatidylethanolamine (NAPE) was recently shown to be synthesized in vitro in cottonseed microsomes by the direct N-acylation of phosphatidylethanolamine (PE) with unesterfied fatty acids (K.D. Chapman and T. S. Moore, 1993, Plant Physiol. 102, 761-769). Here we examine 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 [1-14C]palmitic acid independent of exogenously supplied ATP. O-Acylation of PE and phosphatidylcholine (PC) with [1-14C]palmitic acid proceeded only in the presence of ATP. Further radiolabeling experiments with [1-14C]palmitoylCoA and phosphatidyl(N-[1-14C]-palmitoyl)ethanolamine indicated that O-acylation of phospholipids occurred via an acylCoA intermediate and not via an NAPE intermediate. [1-14C]palmitic acid was released from PC[1-14C-dipalmitoyl] in cottonseed microsomes in a Ca(2+)-dependent manner and this [14C]-FFA was incorporated into [14C]NAPE in a linear fashion. Cottonseed NAPE was selectively hydrolyzed to N-acylethanolamine (NAE) and N-acyl lysophosphatidylethanolamine (NAlysoPE) by Ca(2+)-independent, membrane-bound phospholipase D and A activities, respectively. NAlysoPE was not hydrolyzed to NAE, indicating that the phospholipase D that was active toward NAPE did not recognize NAlysoPE; instead NAlysoPE was converted to NAPE in the presence of Ca2+. Collectively, our results indicate that NAPE synthesis and the O-acylation of other phospholipids 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.
Chapman
K D
KD
Department of Biological Sciences, University of North Texas, Denton 76203, USA.
Lin
I
I
DeSouza
A D
AD
D000215:Acylation; D002250:Carbon Radioisotopes; D002855:Chromatography, Thin Layer; D003368:Gossypium / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D008563:Membrane Lipids / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism*; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000378:metabolism; D010714:Phosphatidylethanolamines / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D012639:Seeds / Q000378:metabolism*; D013997:Time Factors
D002250:Carbon Radioisotopes; D008563:Membrane Lipids; D010169:Palmitic Acids; D010714:Phosphatidylethanolamines; D010743:Phospholipids; D019308:Palmitic Acid