Departments of Botany and Plant Pathology and of Biological Sciences, Purdue University, Lafayette, Indiana 47907.
Plant Physiol. 1970 Jun;45(6):800-4. doi: 10.1104/pp.45.6.800.
Enzymatic activities of the cytidine 5'-diphosphate choline pathway for lecithin biosynthesis were demonstrated in homogenates of onion stem (Allium cepa). Choline kinase activity was present in the postmicrosomal supernatant, with less than 3% sedimenting with the particulate fractions. Phosphorylcholine-cytidyl transferase was distributed among all fractions, and phosphorylcholine-glyceride transferase was predominantly found in the particulate fraction.The phosphorylcholine-cytidyl transferase activity of onion stem required a divalent ion (Mg(2+) or Mn(2+)) for activity, was inhibited by Ca(2+), and was specific for cytidine triphosphate, with optimal activity in the range pH 6 to 7. To evaluate the distribution among cell fractions, conditions of pH, cofactors, substrate, and assay were optimized for each fraction. One-third of the transferase activity sedimented with the mitochondria-proplastids fraction, and one-third was in the microsomal supernatant. The dictyosome fraction contained about 10% of the total activity but showed a greater specific activity than the other fractions. Similar results were obtained with homogenates from rat liver, in that purified Golgi apparatus fractions contained the highest phosphorylcholine-cytidyl transferase activity on a protein basis when compared with other cell fractions at pH 7.2.
在洋葱茎（Allium cepa）的匀浆中证明了胞苷 5'-二磷酸胆碱途径的卵磷脂生物合成的酶活性。胆碱激酶活性存在于微粒体上清液中，不到 3%的部分与颗粒部分一起沉降。磷酸胆碱胞苷转移酶分布在所有部分中，而磷酸胆碱甘油酯转移酶主要存在于颗粒部分。洋葱茎的磷酸胆碱胞苷转移酶活性需要二价离子（Mg（2+）或 Mn（2+））才能发挥活性，被 Ca（2+）抑制，并且对胞苷三磷酸具有特异性，最适 pH 范围为 6 至 7。为了评估细胞部分之间的分布，优化了每个部分的 pH、辅助因子、底物和测定条件。三分之一的转移酶活性与线粒体-前质体部分一起沉淀，三分之一存在于微粒体上清液中。高尔基器部分含有约 10%的总活性，但比其他部分具有更高的比活性。用大鼠肝匀浆获得了类似的结果，即与其他细胞部分相比，在 pH 7.2 时，纯化的高尔基体部分在蛋白质基础上具有最高的磷酸胆碱胞苷转移酶活性。
