Chapman K D, Lin I, DeSouza A D
Department of Biological Sciences, University of North Texas, Denton 76203, USA.
Arch Biochem Biophys. 1995 Apr 20;318(2):401-7. doi: 10.1006/abbi.1995.1246.
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.
最近有研究表明，在棉籽微粒体中，N-酰基磷脂酰乙醇胺（NAPE）可通过磷脂酰乙醇胺（PE）与未酯化脂肪酸直接进行N-酰化反应在体外合成（K.D. 查普曼和T.S. 摩尔，1993年，《植物生理学》第102卷，第761 - 769页）。在此，我们研究了棉籽微粒体中NAPE的合成与周转和其他膜磷脂O-酰化之间的关系。PE以时间依赖性方式与[1-14C]棕榈酸进行N-酰化反应，且不依赖于外源供应的ATP。PE和磷脂酰胆碱（PC）与[1-14C]棕榈酸的O-酰化反应仅在ATP存在时进行。进一步用[1-14C]棕榈酰辅酶A和磷脂酰（N-[1-14C]-棕榈酰）乙醇胺进行的放射性标记实验表明，磷脂的O-酰化反应通过酰基辅酶A中间体进行，而非通过NAPE中间体。[1-14C]棕榈酸在棉籽微粒体中以Ca(2+)依赖的方式从PC[1-14C-二棕榈酰]中释放出来，且这种[14C]-游离脂肪酸以线性方式掺入[14C]NAPE中。棉籽NAPE分别通过不依赖Ca(2+)的膜结合磷脂酶D和A的活性，选择性地水解为N-酰基乙醇胺（NAE）和N-酰基溶血磷脂酰乙醇胺（NAlysoPE）。NAlysoPE不会水解为NAE，这表明对NAPE有活性的磷脂酶D不识别NAlysoPE；相反，在Ca2+存在时，NAlysoPE会转化为NAPE。总体而言，我们的结果表明，NAPE的合成和其他磷脂的O-酰化反应通过两条独立的途径进行，且微粒体NAPE通过膜结合磷脂酶活性被选择性地周转。本文概述了棉籽NAPE的代谢途径。
