RUI: Tetrahymena: A Model for Eukaryotic Phospholipid Metabolism

这项研究将继续开发利用纤毛虫原生动物嗜热四膜虫作为研究真核生物磷脂代谢的模式系统。研究的重点是磷脂酰乙醇胺和磷脂酰胆碱生物合成途径之间的相互关系，特别是阐述了新发现的乙醇胺和胆碱激酶之间的交叉调节，其中磷酸胆碱被证明激活了乙醇胺激酶。这一调节在体内的可能作用将通过检测在正常生长条件下和在这些中间体水平可能被扰动的条件下(通过使用胆碱和乙醇胺的类似物)途径中的中间体(乙醇胺、乙醇胺磷酸、CDP-乙醇胺、胆碱、磷酸胆碱和CDP-胆碱)的水平来研究。这一结果将阐明磷脂生物合成途径中中间体代谢通道的潜力。还将研究来自牛肝脏的酶，如乙醇胺激酶和胆碱激酶，以阐明四膜虫和高等真核生物在磷脂生物合成方面的异同。脂质在生物膜结构和功能中的作用在相当长的一段时间内一直是人们主要关注的问题。脂类的物理状态和给定膜中脂类的类型的改变使人们对膜的流动性、表面电荷和极性头基的要求有了一些了解。所有这些方面似乎对给定的膜系统的正常运行都很重要。真核生物的磷脂组成因组织的不同而不同，在给定的组织内从细胞类型到细胞类型，甚至在给定的细胞中的膜类型之间也是不同的。真核生物中磷脂组成的这些差异是如何产生的，一直是人们非常感兴趣的问题，并与临床上的一些问题有关，如人肺中表面活性物质二棕榈酰磷脂酰胆碱的形成缺陷。这项研究探索了磷脂生物合成的第一反应(乙醇胺和胆碱激酶)，这些反应在不同组织和生物体之间表现出极大的结构和性质差异。这些差异表明，在某些组织的磷脂生物合成途径中，这一步可能存在额外的调节。这种可能性将在四膜虫(一种单细胞真核生物)中得到检验，其磷脂合成途径与哺乳动物相同。这项研究将广泛地涉及本科生，并将使他们接触到密集的实验室经验，这些经验将在他们未来的科学职业生涯中积累起来。

This research will continue to develop the use of the ciliate protozoan Tetrahymena thermophila as a model system for the study of eukaryotic phospholipid metabolism. The research focuses on the interrelationships between the pathways of phosphatidylethanolamine and phosphatidylcholine biosynthesis, with particular emphasis on elaborating the newly-discovered cross-regulation between ethanolamine kinase and choline kinase in which choline phosphate has been shown to activate ethanolamine kinase. The possible role of this regulation in vivo will be investigated by examining levels of the intermediates in the pathways (ethanolamine, ethanolamine phosphate, CDP-ethanolamine, choline, choline phosphate and CDP- choline) under normal growth conditions and under conditions in which the levels of these intermediates may be perturbed (by using analogs of choline and ethanolamine.) The results will elaborate the potential for metabolic channelling of intermediates in the phospholipid biosynthetic pathways. Enzymes from bovine liver, such as the ethanolamine kinase and choline kinase will also be examined in order to elaborate similarities and differences in phospholipid biosynthesis between Tetrahymena and higher eukaryotes. The role of lipids in the structure and function of biological membranes has been of major interest for a considerable period of time. Modifications of the physical state of lipids and of the types of lipids in a given membrane have led to some understanding of requirements for membrane fluidity, surface charge and polar head groups. All of these aspects appear to be important to normal operation of a given membrane system. The phospholipid composition of eukaryotes varies from tissue to tissue, from cell type to cell type within a given tissue and even between membrane types with in a given cell. How these differences in phospholipid composition in eukaryotes arise has been of considerable interest and relates to such clinical problems as defects in formation of the surfactant dipalmitoylphosphatidylcholine in the human lung. This research explores the first reactions in phospholipid biosynthesis (ethanolamine and choline kinases) which exhibit great variability in structure and properties between various tissues and between organisms. These differences suggest possible additional regulation at this step in the phospholipid biosynthetic pathways in some tissues. This possiblity will be examined in Tetrahymena (a unicellular eukaryote) whose pathways for pospholipid biosynthesis are the same as those in mammals. The research will extensively involve undergraduates and will expose them to the intensive laboratory experience which they will encournter in their funther scientific careers.