高中生物奥赛辅导生化——三羧酸循环

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琥珀酰CoA
琥珀酰CoA合成酶 （也称琥珀酸硫激酶）
琥珀酸
The third example of substrate-level phosphorylation. 琥珀酸是对称分子,没有了手性.
3.3.1.6 Succinate is oxidized to fumarate (延胡索酸) 琥珀酸脱氢酶
柠檬酸合酶
草酰乙酸
柠檬酸
The hydrolysis the high energy thioester(硫酯) drives the reaction.
合酶与合成酶
• 合酶 (synthase)：
– 催化加合反应，促使合成
• 合成酶 (synthetase)：
– 催化连接反应，一般需要NTP
3.3.1.2 Citrate isomerizes to isocitrate (异柠檬酸) via cis-aconitate (顺乌头酸)
3.2 Pyruvate is oxidized to acetyl-CoA
• Pyruvate is transported into mitochondria（线粒体）
then oxidized to acetyl-CoA (releasing CO2) before
entering the citric acid cycle
立体异构体 马来酸
琥珀酸
延胡索酸
The free energy change of this reaction is insufficient to reduce NAD+. Succinate Dehydrogenase is directly linked with the electron transport chain.
Pyruvate is oxidized and acetate is transferred to CoA.
Acetyl CoA enters the TCA cycle. Acetate is oxidized to CO2.
Pyruvate is oxidized and acetate is transferred to CoA.
synthesis and decomposition net. 所有中间代谢产物在代谢中没有净合成或净降解.
3.4 The energetic of the aerobic decomposition of glucose 葡萄糖有氧分解途径的能量计算
1. Acetyl in acetyl-S-CoA was oxydized: 化学氧化释放的自由能：874.9 kJ/mol 生物氧化释放的自由能：520.9 kJ/mol 用于ATP合成的自由能：354 kJ/mol
乙酰CoA 草酰乙酸 柠檬酸 顺乌头酸 异柠檬酸
苹果酸 延胡索酸 a-酮戊二酸 琥珀酸
琥珀酰CoA
乙酰CoA 草酰乙酸 柠檬酸
苹果酸
顺乌头酸
异柠檬酸 延胡索酸
琥珀酸
a-酮戊二酸
琥珀酰CoA
3.3.1.1 The cycle begins with the condensation of acetyleCoA and oxaloacetate to form citrate
Acetyl CoA enters the TCA cycle. Acetate is oxidized to CO2.
Pyruvate is oxidized and acetate is transferred to CoA.
Acetyl CoA enters the TCA cycle. Acetate is oxidized to CO2.
使用高度提纯的酶在体外实验证明了这一代谢途径
• Also by isotope tracer experiments in vivo; 通过体内同位素示踪法也证明了这一代谢途径
3.3.2 Survey of TCA cycle
1. 总反应式:
O CH3-C-SCoA + 3NAD+ + FAD + GDP + Pi 2CO2 + 3NADH•H+ + 1FADH2 + 1GTP + CoA-SH 2. There are two carbon atoms in the form of acetyl-SCoA enters every cycle; and there are two decarboxylations take place in each cycle; 乙酰辅酶A中的二碳乙酰基进入TCA循环；在循环中发生 两次脱羧反应. Notice: the 2 carbon atoms entering the cycle are not the same as those leaving the cycle
酶活性中心的 只能结合底物的 一部分,底物的部 分具有手性,分子 局部的手性，即 分子的前手性.
前手性、潜手性（pro-chiral)
3.3.1.3 Isocitrate undergoes oxidative decarboxylation (氧化脱羧) to form a-ketoglutarate (a-酮戊二酸)
Aconitase (乌头酸酶)
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90%
4%
6%
G0’ = 8.4 kJ/mol
G0’ = -2.1 kJ/mol
Fluoride citrate（氟柠檬酸） is the special inhbitor of aconitase
3.3.1.2 Citrate isomerizes to isocitrate via cis-aconitate
A methylene group (CH2) is converted to a carbonyl group (C=O).
The citric acid cycle was confirmed to be universal in cells TCA循环被证明在细胞中是广泛存在的
• Details worked out by studying highly purified enzymes of the cycle in vitro;
3. Aerobic catalysis of carbohydrate and tricarboxylic acid cycle 第三节 糖的有氧分解与三羧酸循环
丙酮酸脱羧，乙酰辅酶A的氧化 均发生在线粒体的基质。
ATP的合成在线粒体的内膜上进行的
3.1 A survey of introduction 概述
H 2O
Citrate+ CoA-SH
Succidate + CoA-SH Matalte
H 2O
3.4 The energetic of the aerobic decomposition of glucose
3. Dehydrogenations in oxydation of glucose:
Ⅰ Ⅱ
NAD+ NADH +H+
Pyruvate
CoA-SH CO2
Acetal-CoA TCA Cycle
acetyl-CoA is oxidized
Ⅲ
CO2 + H2O
3.1.2 三羧酸循环的研究简史
The Nobel Prize in Physiology or Medicine 1953
"for his discovery of the citric acid cycle"
百度文库
3.3.2 Survey of TCA cycle
3. There are four dehydrogenation reactions take place in each cycle;
在循环中发生四次脱氢反应(3NADH,1FADH2)
4. There is a substrate level phosphoralation; 循环中发生一次底物水平磷酸化
丙酮酸脱氢酶系
Regulation of pyruvate dehydrogenase complex
砷化物对机体的毒害不仅限于糖酵解，它与丙酮酸
脱氢酶复合物中E2辅基硫辛酰胺的巯基发生共价结合，
使还原型硫辛酰胺形成失去催化能力的砷化物。
3.3 Tricarboxylic Acid Cycle
3.3.1 Reaction process of tricarboxylic acid cycle (三羧酸循环,柠檬酸循环)
丙二酸
琥珀酸（丁二酸）
3.3.1.7 Fumarate is hydrated to L-malate (苹果酸) 延胡索酸酶
延胡索酸
苹果酸
Hydration(水合)
3.3.1.8 Oxaloacetate (草酰乙酸) is regenerated by the oxidation of L-malate (苹果酸)
a-酮戊二酸脱氢酶系
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第二次脱氢,第二次脱羧.E1酶不受磷酸共价调节. Reaction requires TPP and lipoate etc(6种辅酶).
3.3.1.5 Cleavage of the thioester bond (硫酯键) in succinylCoA is coupled to GTP (or ATP) formation
354 40.5% 874 .9
3.4 The energetic of the aerobic decomposition of glucose
2. Hydrations in TCA-cycle:
H 2O
The third H2O entered in TCA cycle:
Citryl-CoA+H20 succinyl-CoA + H2O Fumarate+H20
• 三羧酸循环（ Tricarboxylic acid cycle) TCA Cycle • Kreb’s循环（ Kreb’s cycle) • 柠檬酸循环（Citric cycle)
3.1.1 葡萄糖的有氧分解包括三个部分
Glucose
Glycolysis Yielding of acetyl-CoA
苹果酸脱氢酶
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The standard free energy of this reaction is very positive. The oxidation of malate is driven by the efficient removal of the products.
The last three reactions of the of the TCA cycle The last three reactions of the of the TCA cycle are similar to fatty acid degradation and synthesis, and some amino acid degradations. oxidation – hydration – oxidation.
异柠檬酸脱氢酶
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Reaction 4 and 5
Isocitrate is oxidized (第一次脱氢) and decarboxylated.(第一次脱羧)
3.3.1.4 a-ketoglutarate undergoes oxidative decarboyxlation to form succinyl-CoA (琥珀酰CoA)
3.3.1.6 Succinate is oxidized to fumarate (延胡索酸) 1. The enzyme catalyzes stereospecific dehydrogenation 2. Malonate (丙二酸) is the inhibitor of the reaction
3.3.2 Survey of TCA cycle
5. The reactions catalyzed by aconitase and fumarase is asymmetry reactions;
顺乌头酸酶和延胡索酸酶等催化非对称反应
6. All of the intermediary metabolisms are not
In EMP: In formation of acetyl-CoA: In TCA cycle: C6H12O6 2×pyruvate 2 × CoA-SH 2×pyruvate + 4H 2×acetyl-CoA + 4H +2CO2 16H + 4CO2 2 × CoA-SH