Characterization and Reevaluation of Initial Reactions of Fatty Acid Biosynthesis in Plants

最初参与植物脂肪酸生物合成的序列反应必须根据菠菜中存在以前未报道的3-酮脂酰-ACP合酶（sc-KAS）的发现重新评估。这种酶对短链脂肪酸具有特异性，并且可以通过其对抗生素浅蓝菌素和硫乳霉素的敏感性而与其他3-酮脂酰-ACP脱氢酶区分开。基于E.在大肠杆菌中，以及在菠菜中的这项工作中，有强有力的证据表明这种酶在该序列中取代了乙酰基转酰酶，乙酰基转酰酶是脂肪酸合成中的一种限速反应。这项建议的目的是广泛的生化分析sc-KAS从菠菜和分离的结构基因sc-KAS。虽然对植物中脂肪酸生物合成的调控知之甚少，但有体外证据表明序列的初始反应可以影响产物的脂肪酸组成。sc-KAS可能在这一过程中发挥关键作用，是我们理解监管的关键。在过去的25年里，脂肪酸的生物合成被描述为一系列由酶复合物脂肪酸合成酶催化的反应。根据该途径，乙酰基转酰酶是该反应中的关键限速酶。然而，3-酮脂酰-ACP合酶的发现对这一系列反应提出了挑战。据信后一种酶负责目前认为由乙酰基转酰酶催化的步骤，这与公认的脂肪酸生物合成的教条相反。这是一个重要的发现，将通过纯化，表征和检查这种酶的调节进行研究。了解这种酶在脂肪酸合成中的作用非常重要，特别是在油料作物的生产中。如果可以通过基因工程控制这种酶的表达，则存在过量生产脂肪酸的可能性。即使石油含量只增加一点点，也会产生重大的经济影响。

The sequence reactions initially involved in fatty acid biosynthesis in plants must be reevaluated in light of the discovery that there is in spinach a previously unreported 3- ketoacyl-ACP synthase (sc-KAS). This enzyme is specific for short chain fatty acids and can be distinguished from other 3- ketoacyl-ACP synthases by its sensitivity to the antibiotics cerulenin and thiolactomycin. Based on work carried out with E. coli, as well as this work with spinach, there is strong evidence that this enzyme replaces in this sequence the enzyme acetyl transacylase, a proposed rate-limiting reaction in fatty acid synthesis. The objectives of this proposal are an extensive biochemical analysis of sc-KAS from spinach and isolation of the structural gene for sc-KAS. While the regulation of fatty acid biosynthesis in plants is poorly understood, there is in vitro evidence that the initial reactions of the sequence can influence the fatty acid composition of the products. The sc-KAS may play a critical role in this process and be the key to our understanding of regulation. For the past 25 years, fatty acid biosynthesis has been illustrated as a series of reactions catalyzed by the enzyme complex, fatty acid synthase. According to the pathway, the enzyme, acetyl transacylase is a key rate-limiting enzyme in this reaction. However, the discovery of the enzyme, 3-ketoacyl-ACP synthase, is challenging this series of reactions. It is believed that the latter enzyme is responsible for the step currently thought to be catalyzed by acetyl transacylase, contrary to the accepted dogma of fatty acid biosynthesis. This is a significant discovery that will be investigated through purification,characterization, and examination of the regulation of this enzyme. Understanding the role of this enzyme in fatty acid synthesis is of importance, particularly in the production of oilseed crops. If expression of this enzyme can be controlled through genetic engineering, there is the potential for over- production of fatty acids. Even if only a small increase in oil content could be achieved, it would have a major economic impact.