Albert D H, Snyder F
J Biol Chem. 1983 Jan 10;258(1):97-102.
1-Alkyl-2-acyl-sn-glycero-3-phosphocholine (alkyl-acyl-GPC) comprises 11% of the total phospholipids of rat alveolar macrophages. This endogenous pool of alkylacyl-GPC was prelabeled by incubating the macrophages with [1,2-3H]alkyllyso-GPC (54 Ci/mmol), which enters the cells and is acylated. The effect of various stimuli on the synthesis and release into the media of labeled alkylacetyl-GPC (platelet-activating factor) from the cells was used to establish the role of inactive alkylacyl-GPC as a precursor of the biologically active derivative. A phagocytic agent (zymosan, 100 micrograms/ml) and an ionophore (A23187, 2 microM) stimulated the release of both alkylacetyl-GPC and alkyllyso-GPC into the media at the expense of cellular alkylacyl-GPC. Phospholipase A2 activity (at pH 4.5 and in 1 mM EDTA) was also increased in the media. The stimulatory effect of zymosan and the ionophore on alkylacetyl-GPC release was prevented by mepacrine (0.1 mM), an agent that inhibits the release of fatty acids from phospholipids. These data indicate that phospholipase activity is required for the biosynthesis of alkylacetyl-GPC. However, since the inhibitory effect of mepacrine was not apparent when acetate was present, it appears that the acetylation step is rate limiting. Exposure of alveolar macrophages in culture to zymosan or A23187 stimulated acetyltransferase activity 250-300%. In contrast, phorbol myristate acetate (1.6 microM), which stimulated the accumulation of lysophospholipids but not the level of alkylacetyl-GPC in the media, did not substantially increase acetyltransferase activity. We conclude that alkylacyl-GPC serves as a precursor of alkylacetyl-GPC and that the production of this potent mediator by rat alveolar macrophages can be stimulated by agents that affect phospholipase A2 and acetyltransferase activities. The latter enzyme appears to have a regulatory function in the biosynthesis of alkylacetyl-GPC.
1-烷基-2-酰基-sn-甘油-3-磷酸胆碱（烷基-酰基-GPC）占大鼠肺泡巨噬细胞总磷脂的11%。通过用[1,2-³H]烷基溶血-GPC（54 Ci/mmol）孵育巨噬细胞对这一内源性烷基-酰基-GPC库进行预标记，该物质进入细胞并被酰化。利用各种刺激对细胞中标记的烷基乙酰-GPC（血小板活化因子）的合成及释放到培养基中的影响，来确定无活性的烷基-酰基-GPC作为生物活性衍生物前体的作用。一种吞噬剂（酵母聚糖，100微克/毫升）和一种离子载体（A23187，2微摩尔）以细胞内烷基-酰基-GPC为代价，刺激了烷基乙酰-GPC和烷基溶血-GPC释放到培养基中。培养基中的磷脂酶A2活性（在pH 4.5和1 mM EDTA条件下）也有所增加。酵母聚糖和离子载体对烷基乙酰-GPC释放的刺激作用被米帕林（0.1 mM）阻止，米帕林是一种抑制脂肪酸从磷脂中释放的试剂。这些数据表明磷脂酶活性是烷基乙酰-GPC生物合成所必需的。然而，由于当存在乙酸盐时米帕林的抑制作用不明显，似乎乙酰化步骤是限速步骤。培养的肺泡巨噬细胞暴露于酵母聚糖或A23187下可刺激乙酰转移酶活性250 - 300%。相比之下，佛波酯肉豆蔻酸酯（1.6微摩尔）刺激了溶血磷脂的积累，但未刺激培养基中烷基乙酰-GPC的水平，也未显著增加乙酰转移酶活性。我们得出结论，烷基-酰基-GPC作为烷基乙酰-GPC的前体，大鼠肺泡巨噬细胞产生这种强效介质可受到影响磷脂酶A2和乙酰转移酶活性的试剂的刺激。后一种酶似乎在烷基乙酰-GPC的生物合成中具有调节功能。
