食品专业英语Lesson-6课文与讲解.docx

Lesion 6 Amino Acids (1) 课题引入（时间：5分钟）：1、结合营养学上氨基酸的知识，说明氨基酸类英文资料的必要性。讲授新内容一、例文中第一部分的翻译学习（时间：20分钟）氨基酸的生产有很多途径，包括直接发酵法、用细胞或酶合成前提的方法、蛋白水解物抽提法和化学合成法。重要的非食品用氨基酸包含L-精氨酸、L-谷氨酰胺、 L-组氨酸、 L-亮氨酸、 L-苯丙氨酸、 L-酪氨酸和L-缬氨酸。表1指在食品工业中，生产氨基酸的每年的产量、方法和应用目的。在食品和饲料工业中，氨基酸具有诸如作为营养素和提高风味的多种用途。Amino acids are produced using a range of technologies including direct fermentation, biotransformation of precursors using cells or enzymes, extraction of protein hydrolysates and chemical synthesis. They have a variety of uses as nutrients and flavours in the food and feed industries. Table 1 indicates the annual demand, production methods and applications of amino acids in the food industry. Important amino acids with non-food applications include L-arginine, L-gludtamine, L-histidine, L-leucine, L-phenylalanine, L-tyrosine and L-valine.二、例文中第二部分的翻译学习（时间：10分钟）L-天冬酰胺、L-亮氨酸、L-酪氨酸、L-半胱氨酸和L-胱氨酸的生产是对蛋白水解物的提纯方法。在发酵或生物合成的生产过程中，现已经可以生产除甘氨酸、L-半胱氨酸和胱氨酸之外所有的氨基酸了，但并不是所有的生产方法都可进行商业生产。While fermentation or biotransformation processes have been developed for production of all amino acids except glycine, L-cysteine and L-cystine, not all of these processes are commercially viable. L-asparagine, L-leucine, L-tyrosine, L-cysteine, and L-cystine are produced by purification of protein hydrolysates. Chemical synthesis is more economical for production of optically-inactive racemic mixtures of D- and L-isomers, and D, L-Methionine, D, L-tryptophan and glycine are produced in this way. Processing involving amino acylase enzymes may be used to resolve these racemic mixtures.在上述生产中，可以使用氨基转移酶来解决消除外消旋混合物的产生。化学合成方法更适宜生产不旋光的外消旋混合物D-和L-异构体，如D、L-蛋氨酸，D、L-色氨酸和甘氨酸。棒状杆菌属短杆菌属三、例文中第二部分的翻译学习（时间：40分钟）商业上生产氨基酸的产量就决定于能否成功应用可分泌大量氨基酸的菌株突变体。有两种重要的方法可获得营养缺陷体和调控突变株，或者两者同时缺陷的突变体。自然界分离的这些野生菌株就能够分泌大量的谷氨酸。人们已经认识到，发酵生产氨基酸中重要的菌株来源于棒状杆菌和短杆菌属。由于细胞有代谢调节机制，特别是终产物的抑制作用，野生的种群很少分泌大量水平的氨基酸。 Microbial strains from the genera Croynebacterium and Brevibacterium have assumed major importance in the production of amino acids by fermentation. Natural isolates of these strains can excrete large quantities of glutamic acid. Because of cell metabolic regulatory mechanisms, particularly end-prodcut repression and inhibition, substantial levels of amino acids are rarely excreted by wild-type isolates. Production of commercial quantities of the amino acids has been dependent on the successful development of deregulated mutants. The two most important methods involve use of auxotrophic and regulatory mutants or a combination of the two. Auxotrophic mutants, which lack the enzyme needed to form the regulatory effector metabolite (often the end-product), many accumulate and excrete the metabolic intermediate which is the substrate for the eliminated enzyme. A lysine auxotroph, for example, lacks an enzyme in the pathway necessary for lysine synthesis and requires lysine, or a metabolic precursor which can be converted to lysine, for growth. End-product inhibition by the amino acid 没有支路得生物合成途径生产的氨基酸终产物的抑制作用也许可以通过调控突变体的发展而避免，该调控突变体具有对反馈抑制不敏感的关键酶，从而可以积累某些特殊的氨基酸。product of an unbranched biosynthetic pathway may be avoided by the development of regulatory mutants, having an altered feedback-insensitive key enzyme, thus allowing accumulation of the particular amino acid. Analogues of the end-product, which are also capable of inhibition of the sensitive key enzyme, may be used in screening methods for selection of analogue-resistant or regulatory mutants. Revertants may be selected from auxotrophic mutants (apparently lacking the key regulatory enzyme) which produce a modified deregulated enzyme.终产物类似物也能对抑制敏感的关键酶产生抑制作用；这时可以选择抗类似物的或可调节类似物作用的突变体，来屏蔽此种抑制作用。没有支路得生物合成途径生产的氨基酸终产物的抑制作用也许可以通过调控突变体的发展而避免，该调控突变体具有对反馈抑制不敏感的关键酶，从而可以积累某些特殊的氨基酸。例如，赖氨酸缺陷体，缺少赖氨酸合成途径中的一个酶，必需添加赖氨酸或者其代谢前提才能转化成赖氨酸来满足生长需求。营养缺陷突变体就是缺少某种酶，可调控代谢受体的形成（一般是终产物）；积累或分泌需要的代谢中产物可作为消除该酶抑制反应。从营养缺陷突变体（显然缺失关键调节酶）中筛选回复子，其可意产生一种能更好解除抑制的酶。Lesion 6 Amino Acids (2) Glutamic Acid Production 课题引入（时间：5分钟）：1、结合上节课学习的内容和营养学上氨基酸的知识，说明氨基酸类英文资料的必要性。讲授新内容一、例文中第一段的翻译学习（时间：10分钟）在20世纪初谷氨酸钠的鲜味增强作用在日本被发现， The flavour-enhancing properties of sodium glutamate were discovered in 目前通过谷氨酸钠棒状杆菌发酵来生产，每年世界市场有400000吨。Japan at the start of the twentieth century and a fermentation process for its production by Corynebacterium glutamicum currently supplies and annual world market of about 400 000t.二、例文中第二段的翻译学习（时间：15分钟）谷氨酸生产菌也能利用尿素作为氮源。铵离子浓度必须在介质中维持较低的水平，因为较高浓度对细胞生长和产物形成是有害的。适当氮源，例如铵盐的充足补充是非常必要的，因为NH是氨基酸分子的组成部分。糖蜜或者淀粉水解物通常被用来进行谷氨酸棒状杆菌和相关菌系的谷氨酸商品生产Molasses or starch hydrolysates are generally used for commercial production of glutamic acid by C. glutamicum and related strains. An ample supply of a suitable nitrogen source such as ammonium salts is essential, since NH3 is incorporated into the amino acid molecule. Glutamic acid producing bacteria can also utilize urea as nitrogen source. The concertration of ammonium ion must be maintained at a low level in the medium as higher concentrations are detrimental to cell growth and product formation. The pH of medium tends to drop due to cell glutamate excretion and ammonium ion assimilation, and gaseous ammonia is used as a means of simultaneously medium nitrogen level and a fermentation pH optimum of 7.0-8.0. Glutamate biosynthesis is an aerobic process requiring oxygen throughout the fermentation.谷氨酸盐的生物合成是一个需氧过程，需要通过发酵来获得氧气。气态氨通常被用来作为监测介质中实时氮水平的指标。发酵的最适pH是7.0-8.0。介质中的pH是逐渐降低的，这是由于细胞谷氨酸的释放和铵离子的消耗。谷氨酸生产菌也能利用尿素作为氮源。三、例文中第三段的翻译学习（时间：20分钟）C16-C18饱和脂肪酸抑制乙酰辅酶A羧化酶活性。生物合成通路的第一个酶，随后它又掺入磷脂。生物素是乙酰辅酶A羧化酶的协同因子，乙酰辅酶A羧化酶是油酸（不饱和的，C18：1）这是因为氨基酸的积累主要受它释放速率而不是生物合成速率的影响。饱和脂肪酸甚至在高浓度生物素存在的条件下也能促进谷氨酸盐的积累。过量的生物素在维持足够的生长时，会消弱谷氨酸盐的积累。在生长过程中添加C16-C18氨基酸的积累量达到最大值。但该条件不是达到菌最大生长值的条件。谷氨酸盐生产菌的生长需要生物素，在生物素浓度为0.5g/g细胞（干重）时Glutamate-producing bacteria require biotin for growth but accumulation of the amino acid is maximum at a critical biotin concentration of 0.5g/g cells (dry), which is sub-optimal for maximum growth. Excess biotin, while supporting abundant growth, impairs glutamate accumulation. Addition of C16-C18 saturated fatty acids during growth also permits accumulation of glutamate even in presence of high biotin concentrations. This is because accumulation of the amino acid id primarily controlled by its rate of excretion rather than by its rate of biosynthesis. Biotin is a co-factor of acetyl CoA carboxylase(羧化酶), the first enzyme in the pathway for biosynthesis of oleic acid (unsaturated, C18:1 ) and its subsequent incorporation into phospholipids. C16-C18 saturated fatty acid repress acety CoA carboxylase. Phospholipids appear to regulate the permeability of the cell to glutamate and sub-optimal biotin concentrations or C16-C18 saturated fatty acids to decrease the concentration of phospholipids in the cell, thereby increasing cell permeability to glutamate.磷脂看来具有调节细胞中谷氨酸盐、不适生物素浓度或C16-C18饱和脂肪酸渗透的功能，因此降低细胞中磷脂的浓度，能增加细胞谷氨酸的渗透。生物合成通路的第一个酶，随后它又掺入磷脂。生物素是乙酰辅酶A羧化酶的协同因子，乙酰辅酶A羧化酶是油酸（不饱和的，C18：1）这是因为氨基酸的积累主要受它释放速率而不是生物合成速率的影响。饱和脂肪酸甚至在高浓度生物素存在的条件下也能促进谷氨酸盐的积累。四、例文中第四段的翻译学习（时间：10分钟）在青霉素存在下的谷氨酸生产菌，在过量生物素存在的条件下也能积累大量的谷氨酸盐。 Even in the presence of excess biotin, glutamic acid producing bacteria, grown in the presence of penicillin, can accumulate large amounts of glutamate. Penicillin inhibits bacterial cell-wall synthesis and the enhanced accumulation of glutamate is thought to result from the formation of swollen cells with weakened cell walls, resulting in damage to the permeability barrier of the cell membrane.膜的渗透障碍，提高谷氨酸盐的积累。青霉素抑制细菌细胞壁的合成，导致了肿胀细胞的形成，消弱了细胞壁，破坏了细胞五、例文中第五段的翻译学习（时间：25分钟）对己糖生产谷氨酸进行优化条件，控制EMP途径是最关键的；其是连接糖转化成三羧酸的桥梁。共同协同作用的协同因子，这些对酮戊二酸通过谷氨酸盐脱氢酶转化为谷氨酸盐是必须的。在异柠檬酸盐氧化脱羧转化为酮戊二酸时形成的NADPH+H+提供了减少与NH3但是有充足的氧时，酮戊二酸积累。Under optimized conditions for glutamate production from hexose, the Embden-Meyerhof-Parnas pathway predominates, channeling carbon precusors into the tricarboxylic acid. The NADPH + H+ formed in the oxidative decarboxylation(氧化脱羧) of isocitrate (异柠檬酸盐) to -ketoglutarate provides the reduced co-factor which together with NH3 is required for conversion of -ketoglutarate to glutamate 商品化的谷氨酸生产菌缺乏三羧酸循环酶酮戊二酸脱氢酶，因此在缺乏NH4+by glutamate dehydrogenase. Commercial glutamic acid-producing strains lack the tricarboxylic acid cycle enzyme -ketoglutarate dehydrogenase and consequently, in 但是有充足的氧时，酮戊二酸积累。the absence of NH4+ ions but with sufficient oxygen, -ketoglutarate acid accumulates. Krebs cycle (克雷布斯循环，即三羧酸循环)intermediates, required for replenishment of oxaloacetate needed for the citrate synthase condensation reaction 三羧酸循环高效的补偿反应需要补充草酰乙酸盐，在柠檬酸合成酶的作用下，进行缩合反应和其他的细胞反应。还有一条途径，通过乙醛酸循环的代谢也可以补充三羧酸循环的中间产物。化学计算出，通过乙醛酸循环，1.4摩尔葡萄糖可转化成1摩尔谷氨酸；但该途径通过固定二氧化碳时，每摩尔葡萄糖可产生2摩尔谷氨酸。and