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Acetyl -coenzyme A carboxylase and the regulation of fatty acid synthesis.

机译：乙酰辅酶A羧化酶和脂肪酸合成的调控。

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摘要

While seeds often contain the bulk of a plant's store of fatty acids in the form of triacylglycerols, fatty acids are found throughout plants and fatty acid synthesis (FAS) is one of the primary metabolic pathways. Some plants make "unusual" fatty acids, stored almost exclusively in seeds, which have desirable industrial properties. Factors limiting the use of these oils for industry are (1) plants may not be suitable for crop use and (2) seed may have neither enough total oil, nor a high enough proportion of the unusual fatty acid in the oil, to be cost-effective for industrial use. Current efforts to manipulate both quality and quantity of oil have had mixed results. This is due, in part, to our incomplete knowledge about the components and regulation of FAS in plants. One goal of this thesis has been to extend our understanding of how plants regulate FAS. In plants de novo FAS occurs primarily in plastids and the rate of FAS is regulated in part by acetyl-CoA carboxylase (ACCase). The dicot ACCase investigated in this thesis contains four subunits, one of which, AccD, is encoded on the plastidial genome.;This work presents new data about the regulation of ACCase. In lysates of light-incubated chloroplasts, ACCase activity is at least two-fold higher than from dark-incubated ones. Additionally, acetyl-CoA activates ACCase in a chloroplast lysate. This activation occurs at 10 muM acetyl-CoA, which is similar to the acetyl-CoA concentration found in chloroplasts. When ACCase is assayed in vitro under conditions which simulate the in vivo concentrations of metabolites, ACCase activity is five- to ten-fold lower than that required to sustain known in vivo rates of FAS. Thus, we still have an incomplete understanding of factors which regulate this enzyme.;This thesis also presents a model of the major initial reactions of FAS. This model was built using Stella II software, pool sizes of FAS metabolites, kinetic characterizations of FAS enzymes, and common sense. The simulation allows enzyme expression to be manipulated, either singly or jointly, between 0- and 25-fold. The model's predictions match several results reported from over- and underexpression experiments---even when those results have been non-intuitive. The model predicts that the set of FAS enzymes which limit or co-limit flux vary depending on illumination and products (18:1DeltaA9 or 16:0). The model also predicts a method involving concurrent overexpression of three enzymes by which total FA exported from plastids can be increased.;Finally, this work documents unsuccessful attempts to relocate AccD to the nuclear genome, reports the sequence of Oenothera hookeri AccD, and maps AccD on the plastidial genome of O. hookeri.
机译：尽管种子通常以三酰基甘油的形式包含植物中大部分脂肪酸的存储，但是在整个植物中都发现了脂肪酸，脂肪酸合成（FAS）是主要的代谢途径之一。一些植物产生“不寻常”的脂肪酸，几乎全部存储在种子中，具有理想的工业特性。限制这些油在工业上的使用的因素是：（1）植物可能不适合作物使用；（2）种子可能没有足够的总油，也没有足够高的比例的异常脂肪酸在成本上-工业上有效。当前在控制油的质量和数量上的努力取得了不同的结果。这部分是由于我们对植物中FAS的成分和调节的不完全了解。本文的目标之一是扩展我们对植物如何调节FAS的理解。从头开始，FAS主要在质体中发生，FAS的速率部分受乙酰辅酶A羧化酶（ACCase）调节。本文研究的双子叶植物ACCase包含四个亚基，其中一个AccD编码在质体基因组中。这项工作提供了有关ACCase调控的新数据。在轻度孵育的叶绿体裂解物中，ACCase活性至少比黑暗孵育的叶绿素高出两倍。另外，乙酰辅酶A激活叶绿体裂解物中的ACCase。此激活发生在10μM乙酰辅酶A处，与叶绿体中的乙酰辅酶A浓度相似。当在模拟体内代谢物浓度的条件下体外分析ACCase时，ACCase活性比维持已知FAS体内速率所需的活性低五至十倍。因此，我们对调节这种酶的因素仍然不完全了解。本文还提出了FAS主要初始反应的模型。该模型是使用Stella II软件，FAS代谢物的库大小，FAS酶的动力学特征以及常识建立的。该模拟使酶表达可以在0到25倍之间单独或联合操纵。该模型的预测与过表达和表达不足实验报告的几个结果相匹配-即使这些结果是不直观的。该模型预测，限制或共限制通量的FAS酶组会根据光照和产物（18：1DeltaA9或16：0）而变化。该模型还预测了一种涉及同时表达三种酶的方法，通过该方法可以增加从质体输出的FA的总量。在O. hookeri的质体基因组中

著录项

  • 作者

    Hunter, Sarah Catherine.;

  • 作者单位

    Michigan State University.;

  • 授予单位 Michigan State University.;
  • 学科 Plant biology.;Biochemistry.
  • 学位 Ph.D.
  • 年度 1999
  • 页码 172 p.
  • 总页数 172
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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