Department of Botany, University of Wyoming, Laramie, Wyoming 82071.
Plant Physiol. 1976 Mar;57(3):382-6. doi: 10.1104/pp.57.3.382.
Three pathways for phosphatidylcholine synthesis were assayed in castor bean (Ricinus communis var. Hale) endosperm. Phosphatidylethanolamine: S-adenosylmethionine methyl transferase occurred predominantly in the endoplasmic reticulum fraction, but some activity appeared in the mitochondria. Phosphorylcholine glyceride transferase occurred exclusively in the endoplasmic reticulum. The phosphorylcholine glyceride transferase activity was approximately 20-fold greater than the methylation pathway in the endoplasmic reticulum. No exchange activity was found. The Michaelis constant for the methylation was 31 mum for S-adenosylmethionine; phosphatidylethanolamine promoted the reaction slightly while other intermediates stimulated it by about 50%. The pH optimum was 9. Phosphorylcholine glyceride transferase had a Michaelis constant of 9.7 mum for cytidine diphosphate choline but variable results were obtained from diglycerides. The pH optimum was 7.5 and a divalent cation was required, Mg(2+) giving the greatest stimulation.
我们检测了蓖麻（Ricinus communis var. Hale）胚乳中三种磷酯酰胆碱的合成途径。磷酸乙醇胺：S-腺苷甲硫氨酸甲基转移酶主要存在于内质网部分，但也有部分活性存在于线粒体中。磷酸胆碱甘油转移酶仅存在于内质网中。磷酸胆碱甘油转移酶的活性大约是内质网中甲基化途径的 20 倍。没有发现交换活性。甲基化的米氏常数为 S-腺苷甲硫氨酸的 31 微米；磷酸乙醇胺略微促进反应，而其他中间产物则刺激反应约 50%。最适 pH 值为 9。磷酸胆碱甘油转移酶对胞苷二磷酸胆碱的米氏常数为 9.7 微米，但从双甘油得到的结果不同。最适 pH 值为 7.5，需要二价阳离子，其中 Mg(2+) 的刺激作用最大。
