Kuwae T, Schmid P C, Johnson S B, Schmid H H
Hormel Institute, University of Minnesota, Austin 55912.
J Biol Chem. 1990 Mar 25;265(9):5002-7.
Phospholipid acyl turnover was assessed in mouse peritoneal exudate cells which consisted primarily of macrophages. The cells were incubated for up to 5 h in media containing 40% H218O, and uptake of 18O into ester carbonyls of phospholipids was determined by gas chromatography-mass spectrometry of hydrogenated methyl esters. The uptake was highest in choline phospholipids and phosphatidylinositol, less in ethanolamine phospholipids, and much less in phosphatidylserine. Acyl groups at the sn-1 and sn-2 positions of diacyl glycerophospholipids, including arachidonic and other long-chain polyunsaturated fatty acids, acquired 18O at about the same rate. Acyl groups of alkylacyl glycerophosphocholine exhibited lower rates of 18O uptake, and acyl groups of ethanolamine plasmalogens (alkenylacyl glycerophosphoethanolamines) acquired only minimal amounts of 18O within 5 h, indicating a low average acyl turnover via free fatty acids. Pulse experiments with exogenous 3H-labeled arachidonic acid supported the concept that acylation of alkenyl glycerophosphoethanolamine occurs by acyl transfer from other phospholipids rather than via free fatty acids and acyl-CoA. The 18O content of intracellular free fatty acids increased gradually over a 5-h period, whereas in extracellular free fatty acids it reached maximal 18O levels within the first hour. Arachidonate and other long-chain polyunsaturated fatty acids were found to participate readily in deacylation-reacylation reactions but were present only in trace amounts in the free fatty acid pools inside and outside the cells. We conclude that acyl turnover of macrophage phospholipids through hydrolysis and reacylation is rapid but tightly controlled so that appreciable concentrations of free arachidonic acid do not occur.
在主要由巨噬细胞组成的小鼠腹腔渗出细胞中评估磷脂酰基周转情况。将细胞在含有40% H218O的培养基中孵育长达5小时，通过氢化甲酯的气相色谱 - 质谱法测定18O进入磷脂酯羰基的摄取量。胆碱磷脂和磷脂酰肌醇中的摄取量最高，乙醇胺磷脂中的摄取量较少，而磷脂酰丝氨酸中的摄取量则少得多。二酰基甘油磷脂的sn - 1和sn - 2位的酰基，包括花生四烯酸和其他长链多不饱和脂肪酸，以大致相同的速率摄取18O。烷基酰基甘油胆碱的酰基表现出较低的18O摄取速率，而乙醇胺缩醛磷脂（烯基酰基甘油磷酸乙醇胺）的酰基在5小时内仅摄取极少量的18O，表明通过游离脂肪酸的平均酰基周转较低。用外源3H标记的花生四烯酸进行的脉冲实验支持了这样的概念，即烯基甘油磷酸乙醇胺的酰化是通过从其他磷脂进行酰基转移而不是通过游离脂肪酸和酰基辅酶A发生的。细胞内游离脂肪酸的18O含量在5小时内逐渐增加，而细胞外游离脂肪酸的18O含量在第一小时内达到最高水平。发现花生四烯酸和其他长链多不饱和脂肪酸很容易参与脱酰基 - 再酰基化反应，但在细胞内外的游离脂肪酸池中仅以痕量存在。我们得出结论，巨噬细胞磷脂通过水解和再酰基化的酰基周转很快，但受到严格控制，因此不会出现可观浓度的游离花生四烯酸。
