Anceschi M M, Di Renzo G C, Venincasa M D, Bleasdale J E
Biochem J. 1984 Nov 15;224(1):253-62. doi: 10.1042/bj2240253.
When type II pneumonocytes from adult rats were maintained in a medium that lacked choline, the incorporation of [14C]glycerol into phosphatidylcholine was not greatly diminished during the period that the cells displayed characteristics of type II pneumonocytes. Cells that were maintained in choline-free medium that contained choline oxidase and catalase, however, became depleted of choline and subsequent synthesis of phosphatidylcholine by these cells was responsive to choline in the extracellular medium. Incorporation of [14C]glycerol into phosphatidylcholine by choline-depleted cells was stimulated maximally (approx. 6-fold) by extracellular choline at a concentration (0.05 mM) that also supported the greatest incorporation into phosphatidylglycerol. The incorporation of [14C]glycerol into other glycerophospholipids by choline-depleted cells was not increased by extracellular choline. When cells were incubated in the presence of [3H]cytidine, the choline-dependent stimulation of the synthesis of phosphatidylcholine and phosphatidylglycerol was accompanied by an increased recovery of [3H]CMP. This increased recovery of [3H]CMP reflected an increase in the intracellular amount of CMP from 48 +/- 9 to 76 +/- 16 pmol/10(6) cells. Choline-depleted cells that were exposed to [3H]choline contained [3H]CDP-choline as the principal water-soluble choline derivative. As the extracellular concentration of choline was increase, however, the amount of 3H in phosphocholine greatly exceeded that in all other water-soluble derivatives. Choline-depletion of cells resulted in an increase in the specific activity of CTP:phosphocholine cytidylyltransferase in cell homogenates (from 0.40 +/- 0.15 to 1.31 +/- 0.20 nmol X min-1 X mg of protein-1). These data are indicative that the biosynthesis of phosphatidylcholine is integrated with that of phosphatidylglycerol and are consistent with the proposed involvement of CMP in this integration. The choline-depleted type II pneumonocyte provides a new model for investigating the regulation of CTP:phosphocholine cytidylyltransferase activity.
当将成年大鼠的II型肺细胞维持在缺乏胆碱的培养基中时，在细胞呈现II型肺细胞特征的期间，[14C]甘油掺入磷脂酰胆碱的过程并没有大幅减少。然而，将细胞维持在含有胆碱氧化酶和过氧化氢酶的无胆碱培养基中时，细胞内的胆碱会被耗尽，随后这些细胞合成磷脂酰胆碱的过程会对细胞外培养基中的胆碱产生反应。在浓度为0.05 mM（该浓度也支持[14C]甘油最大程度地掺入磷脂酰甘油）的细胞外胆碱作用下，胆碱耗尽的细胞将[14C]甘油掺入磷脂酰胆碱的过程受到最大程度的刺激（约6倍）。细胞外胆碱不会增加胆碱耗尽的细胞将[14C]甘油掺入其他甘油磷脂的过程。当细胞在[3H]胞苷存在下孵育时，胆碱依赖性地刺激磷脂酰胆碱和磷脂酰甘油的合成伴随着[3H]CMP回收率的增加。[3H]CMP回收率的增加反映了细胞内CMP的量从48±9增加到76±16 pmol/10(6)个细胞。暴露于[3H]胆碱的胆碱耗尽细胞含有[3H]CDP-胆碱作为主要的水溶性胆碱衍生物。然而，随着细胞外胆碱浓度的增加，磷酸胆碱中的3H量大大超过了所有其他水溶性衍生物中的3H量。细胞的胆碱耗竭导致细胞匀浆中CTP：磷酸胆碱胞苷转移酶的比活性增加（从0.40±0.15增加到1.31±0.20 nmol·min-1·mg蛋白质-1）。这些数据表明磷脂酰胆碱的生物合成与磷脂酰甘油的生物合成是整合的，并且与所提出的CMP参与这种整合一致。胆碱耗尽的II型肺细胞为研究CTP：磷酸胆碱胞苷转移酶活性的调节提供了一个新模型。
