Phosphatidylcholine Synthesis in Plants

磷脂酰胆碱在植物中的合成一直是 认为主要通过磷酸化 胆碱，然后转化为CDP胆碱，然后 将磷脂酸酯基团转移到胆碱上， 最终脂质产物。 有人提出了另一种途径 它涉及三个连续的甲基化，利用S- 腺苷-L-甲硫氨酸，其氨基为 磷脂酰乙醇胺 最近的研究表明， 在某些组织中，如蓖麻籽胚乳，胆碱 由通常假定的前体L-丝氨酸产生， 可用于合成磷脂酰胆碱。 此外，本发明还提供了一种方法， 现在有证据表明，在一些组织中， 磷脂酰乙醇胺不作为底物， 甲基化，不像酵母和哺乳动物组织中的情况。 因此，植物在某些方面不同于酵母， 哺乳动物系统中的甲基化的确切途径， 它们的调节，或甲基化方案的某些方面， 在其他系统中没有被检测和检查。 本提案的目标是重新审查这些 详细描述了最初的甲基化酶，试图 确定核苷酸（CDP-）的胆碱来源。 衍生物）途径（以及调节 甲基化途径），并继续我们的研究 转化为核苷酸途径的酶。 我们将 描述甲基化酶的特征，研究它们的 纯化，并测试通过变构调节 和/或膜-酶相互作用以及 磷酸化/去磷酸化。 各种植物器官， 尤其是叶子和根， 合成并输出胆碱或胆碱-P。 磷脂是所有细胞膜的重要组成部分， 活的有机体。 它们在身体的结构和新陈代谢中 作用;但它们的合成途径尚不完全清楚， 尤其是植物。 这个项目提供了机会 阐明磷脂合成的重要途径， 模型工厂系统中的调节。*//

The synthesis of phosphatidylcholine in plants has been thought to occur primarily through phosphorylation of choline, followed by conversion to CDPcholine, and then transfer of a phosphatidate group to the choline to give the final lipid product. An alternate pathway has been proposed which involves three sequential methylations, utilizing S- adenosyl-L-methionine, of the amino group of phosphatidylethanolamine. Recent research has indicated that in some tissues, such as castor bean endosperm, the choline produced from a commonly assumed precursor, L-serine, may not be available for phosphatidylcholine synthesis. In addition, evidence now is available that in several tissues phosphatidylethanolamine does not act as a substrate for methylation, unlike the case in yeast and mammalian tissues. Thus, either plants differ in some respects from yeast and mammalian systems in the exact pathways of methylation and their regulation, or some aspects of the methylation scheme have not been detected and examined in these other systems. The goals of this proposal are to examine these newly described initial methylation enzymes in detail, to try to determine a source of choline for the nucleotide (CDP- derivative) pathway (and for regulation of the functioning of the methylation pathway), and to continue our investigations into the enzymes of the nucleotide pathway. We will characterize the methylation enzymes, work on their purifications, and test for regulation through allosteric and/or membrane-enzyme interactions as well as phosphorylation/dephosphorylation. Various plant organs, particularly leaves and roots, will be tested for a capacity to synthesize and export choline or choline-P. Phospholipids are important components of membranes of all living organisms. They play crucial structural and metabolic role; yet their pathways of synthesis are incompletely known, especially in plants. This project affords the opportunity to elucidate important pathways of phospholipid synthesis and regulation in a model plant system.***//