Studies on the biosynthetic mechanism of platelet-activating factor and its physiological significance in alveolar macrophages

1. 烷基醚磷脂酰化机理的研究。我们研究了1-烷基-甘油酰胆碱（GPC）在兔肺泡巨噬细胞微粒体中的酰化机制，以1-烷基-甘油酰胆碱为受体，以二酰基-GPC（包括2位的^<14 bb0 c -花生四烯酸）为酰基供体。这种转酰基化反应不需要CoA、ATP或Mg^<2+>。C-20脂肪酸，特别是花生四烯酸（20:4）和二十二碳六烯酸（22:6）是该酶反应的良好底物。烷基醚磷脂中花生四烯酸的释放及乙酰基残基掺入1-烷基- gpc。磷脂酶A_2作用于乙醚胆碱甘油磷脂（CGP）产生的Lyso血小板活化因子（Lyso PAF， 1-烷基- gpc）被乙酰转移酶或转酰基酶乙酰化或酰基化，具有竞争性。乙酰转移酶的比活性为474 mol /min/10^6个细胞裂解物（acetylCoA; 100 m）， A23187刺激细胞后比活性提高2-3倍。转酰基酶的活性为98摩尔/分/10^6个细胞裂解液，细胞刺激未见转酰基酶活性显著增加。另一方面，在不添加外源乙酰辅酶a的情况下，乙酰转移酶的活性与乙酰辅酶a的浓度有很大关系。因此，在这种情况下，lyso PAF似乎主要是由转酰基酶以20:4的比例进行酰基化，而不是乙酰转移酶。这些酶或底物在细胞中的定位应在下一步进行研究。

1. Studies on the acylation mechanism of alkylether phospholipids. We studied the acylation mechanism of 1-alkyl-glycerophosphocholine (GPC), using 1-alkyl-GPC as an acceptor and diacyl-GPC, including ^<14>C-arachidonic acid at the 2-position, as an acyl donor, by rabbit alveolar macrophage microsomes. This transacylation reaction does not need CoA, ATP or Mg^<2+>. C-20 fatty acids, especially arachidonic acid (20:4) and docosahexaenoic acid (22:6) are the good substrates for this enzymatic reaction.2. Release of arachidonic acid from alkylether phospholipids and incorporation of acetyl residue into 1-alkyl-GPC. Lyso platelet-activating factor (lyso PAF, 1-alkyl-GPC) produced by phospholipase A_2 action on ether choline glycerophospholipid (CGP) was acetylated or acylated by acetyltransferase or transacylase, competitively. The specific activity of acetyltransferase was 474 pmole/min/10^6cell lysate (acetylCoA; 100 m) and increased by 2-3 times on the cell stimulation with A23187. That of transacylase was 98 pmole/min/10^6cell lysate and significant increase of the activity was not observed on cell stimulation. on the other hand, the acetyltransferase activity was quite dependent on the concentration of acetyl-CoA in the case of no addition of exogenous acetyl-CoA. Therefore, in this case, lyso PAF seemed to be acylated mainly by transacylase with 20:4, rather than by acetyltransferase. The localization of these enzymes or substrates in cells shoud be studied in the next step.