Chapter 3 Metabolism of Carbohydrate 生物化学 Chapter 3 Metabolism of Carbohydrate

Section 1 Digestion and uptaking of carbohydrate 第一节 糖的消化与吸收

1.1 糖类水解酶 多糖水解酶 糖苷水解酶 淀粉酶 纤维素酶 半纤维素酶 果胶酶 麦芽糖酶 蔗糖酶 乳糖酶 ●●● a-淀粉酶 b-淀粉酶 葡萄糖淀粉酶 纤维素酶 多糖水解酶 异淀粉酶 半纤维素酶 果胶酶 麦芽糖酶 蔗糖酶 糖苷水解酶 乳糖酶 ●●●

1.2 糖类在人体中的消化 吸收 第一阶段 第二阶段 糖类食物 唾液淀粉酶 咀嚼、部分水解 有限水解 HCl 胰淀粉酶 a-糊精、麦芽糖和少量葡萄糖 第二阶段 单糖 糖苷酶 吸收

1.3 糖的吸收 糖的吸收就是指游离的葡萄糖（单糖）进入到生物体内（细胞内）的过程。 主动运输 促进扩散 糖的吸收方式 基团转位

血糖的来源、去向 血糖 80－120 mg/100 ml 40－70， 120－180 低 高 Glucose is very soluble source of quick and ready energy. It is a relatively stable and easily transported. Glucose is the only source of energy in red blood cells

Section 2 Catabolism of monocarbohydrate 第二节 单糖的分解代谢 Glycolysis and Gluconeogenesis Glycolysis- Derived from the Greek stem glyk-,”sweet”, and the word lysis, “dissolution”.

2.1 Concepts 酵解（glycolysis): 是酶将葡萄糖降解成丙酮酸并伴随着生成ATP的过程。它是动物、植物、微生物细胞中葡萄糖分解产生能量的共同代谢途径。 发酵（fermentation)：厌氧有机体把酵解生成的NADH中的氢交给丙酮酸，生成乳酸；或丙酮酸脱羧生成的乙醛，生成乙醇。 发酵类型（types of fermentation)。 呼吸（respiration）

Glycolysis The cell is the functional unit of organisms. All metabolic activity is based on cells

2.2 Glycolysis and the Catabolism of Hexoses —— EMP pathway Embden-Meyerhof-Parnas pathway 2.2.1 The Elucidation of Glucose Degradation Pathway Has a Rich History 1890s, Buchner (Germany), fermentation occurred outside living yeast cells (the “sucrose surprise”): metabolism became chemistry; The Nobel Prize in Chemistry 1907 for his biochemical researches and his discovery of cell-free fermentation

2.2.1 The Elucidation of Glucose Degradation Pathway Has a Rich History 1910s to 30s, Embden and Meyerhof (Germany), glycolysis in muscle and its extracts: in vitro reconstruction from glycogen to lactic acid; many reactions of lactic acid (muscle) and alcohol (yeast) fermentations are the same; lactic acid is reconverted to carbohydrate in the presence of O2; some phosphorylated compounds are energy-rich. “Embden-Meyerhof pathway”. 埃姆登- The Nobel Prize in Physiology or Medicine 1922 for his discovery of the fixed relationship between the consumption of oxygen and the metabolism of lactic acid in the muscle 梅耶霍夫 Otto Meyerhof

2.2.1 The Elucidation of Glucose Degradation Pathway Has a Rich History 1940s, Lipmann, discovery of Coenzyme A and acetyl-CoA; 1930s to 40s, Carl Cori and Gerty Cori, discovery of glycogen phosphorylase (磷酸化酶）and glucose-1-phosphate; 1940s, Cori, Cori and Houssay, discovery of hormone （激素） regulation of metabolism; The whole pathway of glycolysis (Glucose to pyruvate) was elucidated by the 1940s.

2.2.2 Overview of glycolysis 糖酵解概况 The glycolysis is a pathway from glucose to pyruvate; 葡萄糖 Yeast 丙酮酸 Exercising muscle The fate of glucose is varies with physiological conditions, tissues, and organisms. Anaerobic conditions Aerobic conditions

2.2.2 Overview of glycolysis 糖酵解概况 2. Glycolysis can occurs under anaerobic conditions (fermentations); Fermentations provide usable energy in t absence of oxygen. 3. glycolysis takes place in cytoplasma （细胞质）； Glucose is an important fuel for most organisms

2.2.2 Overview of glycolysis 4. The glycolysis pathway consists of two phases Preparatary phase (耗能) 2ATP Payoff phase (产能)2×2 ATP Net: 2 ATP； a limited amount

2.2.2 Overview of glycolysis 5. Intermediary metabolites are phosphated（磷酸化的）; 6. Three types of chemical changes； 7. Glycolysis is highly regulated. 碳原子途径 磷酸途径 氧化还原反应的电子途径 Glycolysis is an energy-conversion pathway in many organisms

2.2.2 Overview of glycolysis Glucose is phosphorylated. The negative charge concentrates glucose in the cell and glucose becomes less stable. (P ，C ，e )

8. Types of reactions occurring in glycolysis 2.2.2 Overview of glycolysis 8. Types of reactions occurring in glycolysis Phosphoryl group transfer: kinase(激酶); 激酶 磷酸化酶

8. Types of reactions occurring in glycolysis 2.2.2 Overview of glycolysis 8. Types of reactions occurring in glycolysis Phosphoryl group shift: mutase（变位酶） Phosphoryl shift. A phosphoryl group is shifted from one oxygen atom to another within a molecule by a mutase.

8. Types of reactions occurring in glycolysis 2.2.2 Overview of glycolysis 8. Types of reactions occurring in glycolysis Isomerization: isomerase(异构酶); Isomerization. A ketose (酮糖） is converted into an aldose （醛醣）, or vice versa, by an isomerase.

8. Types of reactions occurring in glycolysis 2.2.2 Overview of glycolysis 8. Types of reactions occurring in glycolysis Dehydration: dehydratase（enolase, 烯醇化酶） Dehydration. A molecule of water is eliminated by a dehydratase.

8. Types of reactions occurring in glycolysis 2.2.2 Overview of glycolysis 8. Types of reactions occurring in glycolysis Aldol cleavage: aldolase（醛缩酶） Aldol cleavage. A carbon-carbon bond is split in a reversal of an aldol condensation by an aldolase.

2.2.2 Overview of glycolysis Phosphoryl group transfer: kinase; Phosphoryl group shift: mutase（变位酶）; Isomerization: isomerase; Dehydrogenation: dehydrogenase（脱氢酶）; Dehydration: dehydratase (enolase，烯醇化酶); Aldol cleavage: aldolase（醛缩酶）.

Preparatory phase: Phosphorylation of glucose and its conversion to glyceraldehyde-3-phosphate Payoff phase Conversion of glyceraldehyde-3-phosphate to pyruvate and the coupled formation of ATP

2.2.3 The reactions of glycolysis 葡萄糖 葡萄糖-6-磷酸 果糖-6-磷酸 果糖-1,6-二磷酸 甘油醛-3-磷酸 二羟丙酮磷酸

二羟丙酮磷酸 甘油醛-3-磷酸 1,3-二磷酸甘油酸 3-磷酸甘油酸 2-磷酸甘油酸 磷酸烯醇式丙酮酸 丙酮酸

Intermediary metabolites are phosphated （磷酸化的） Hexokinase traps glucose in the cell and begins glycolysis 带有负电荷的磷酸基团使中间产物具有极性，从而使这些产物不易透过脂膜而失散。 磷酸基团在各反应步骤中，对酶来说，起到信号基团的作用，有利于与酶结合而被催化。 磷酸基团经酵解作用后，最终形成ATP的末端磷酸基团，因此具有保存能量的作用。

Stage of glycolysis The glycolytic pathway can be divided into three stages: 1)Glucose is trapped and destabilized. 2)Two interconvertible three-carbon molecules are generated by cleavage of six-carbon fructose. 3)ATP is generated. Stage 1 of Glycolysis. The three steps of stage 1begin with the phosphorylation of glucose by hexokinase

(1) Glucose is Phosphorylated First to Enter Glycolysis Hexokinase 己糖激酶 ΔG°’= -4.0 kcal mol-1 Phosphoryl transfer reaction. Kinases transfer phosphate from ATP to an acceptor. Hexokinase has a more general specificity in that it can transfer phosphate to other sugars such as mannose（甘露糖）.

(1) Glucose is Phosphorylated First to Enter Glycolysis ATP与葡萄糖的反应机制 Mg2+-ATP复合物 ( Mg2+-ATP complex)

(1) Glucose is Phosphorylated First to Enter Glycolysis 己糖激酶与葡萄糖结合时的构象变化 Induced fit in hexokinase. As shown in blue, the two lobes of hexokinase are separated in the absence of glucose. The conformation of hexokinase changes markedly on binding glucose, as shown in red. The two lobes of the enzyme come together and surround the substrate.

(1) Glucose is Phosphorylated First to Enter Glycolysis 1、己糖激酶是一种调节酶，产物葡萄糖-6-磷酸和ADP能使该酶受到变构抑制。但葡萄糖磷酸激酶却不受葡萄糖-6-磷酸的抑制。 2、葡萄糖激酶的对葡萄糖的米氏常数Km (5~10mmol/L) 比己糖激酶的Km值 （0.1mmol/L）大得多，因此，当葡萄糖浓度相当高时，葡萄糖激酶才起作用。

动物己糖激酶同工酶的性质比较 Ⅰ Ⅱ Ⅲ Ⅳ 分布 脑、肾 骨骼肌、心肌 肝、肺 只存在肝中 分子量 kD 100 5-6.8 （葡萄糖激酶） 分布 脑、肾 骨骼肌、心肌 肝、肺 只存在肝中 分子量 kD 100 5-6.8 km(mM葡萄糖) 0.05 0.2 0.007 12 km(mM果糖) 3 800 VG(μM/min·ng pr.) 80 40 VF / VG 1.1 1.2 G6p的反馈抑制 ＋ － 无机磷酸解抑制 无机磷酸减缓抑制 柠檬酸激活

(2) Glucose-6-P Isomerizes from an Aldose to a Ketose Phosphoglucose Isomerase 磷酸葡萄糖同分异构酶 ΔG°’= 0.40 kcal/mol The conversion of an aldose（醛糖） to a ketose（酮糖）. 先开环异构化闭环 受6-磷酸-葡萄糖酸抑制（在酸性条件下）

(2) Glucose-6-P Isomerizes from an Aldose to a Ketose Phosphoglucose Isomerase The enzyme opens the ring, catalyzes the isomerization, and promotes the closure of the five member ring.

(3) Fructose-6-P is Further Activated by Phosphorylation Phosphofructokinase PFK（磷酸果糖激酶） The 2nd investment of an ATP in glycolysis. ΔG°’= -3.4 kcal mol-1 PFK is an important allosteric enzyme（别构酶） regulating the rate of glucose catabolism and plays a role in integrating metabolism. Bis means two phosphate groups on two different carbon atoms. Di means two phosphate groups linked together on the same carbon atom.

(3) Fructose-6-P is Further Activated by Phosphorylation 磷酸果糖激酶是一种变构酶，糖酵解的速率严格地依赖该酶的活力水平，它是哺乳动物糖酵解途径最重要的调控关键酶。 肝中PFK受高浓度的ATP的抑制。ATP结合于调节部位。ATP对该酶的别构抑制效应可被AMP解除。因此ATP/AMP的比例关系对此酶有明显的调节作用。

Effectors of phosphofructokinase （PFK） Activators Inhibitors AMP ATP ADP Citrate F6P PEP cAMP phosphocreatine K+ 3PG（甘油酸） NH4+ 2PG （甘油酸） PO43- 2,3BPG （甘油酸） 柠檬酸 磷酸肌酸

(4) Fructose-1,6-Bisphosphate is Cleaved (lysed) in the Middle Aldolase (醛缩酶） 1 4 3 ΔG°’= 5.7 kcal mol-1 Reverse aldol condensation; converts a 6 carbon atom sugar to 2 molecules, each containing 3 carbon atoms.

Stage 2 of glycolysis 果糖-1，6-二磷酸 FBP 二羟丙酮磷酸 （DHAP） 甘油醛-3-磷酸 （GAP）

二羟丙酮磷酸 （DHAP） 甘油醛-3-磷酸 （GAP） (5) Triose phosphate Interconvert Triose phosphate isomerase 丙糖磷酸异构酶 ，TIM ΔG°’ = 1.8 kcal mol-1 二羟丙酮磷酸 （DHAP） 甘油醛-3-磷酸 （GAP）

(5) Triose phosphate Interconvert 甘油醛-3-磷酸

(5) Triose phosphate Interconvert 单烯二羟负 离子中间体 二羟丙酮磷酸 （DHAP） 甘油醛-3-磷酸 （GAP） ΔG°’ = 1.8 kcal mol-1 All the DHAP is converted to glyceraldehyde 3-phosphate（GAP）. Although, the reaction is reversible it is shifted to the right since glyceraldehyde 3-phosphate is a substrate for the next reactions of glycolysis. Thus, both 3-carbon fragments are subsequently oxidized. This structural motif, called an TIM barrel, is also found in others glycolytic enzymes. His 95 and Glu 165 located in the barrel is active site .

Catalytic mechanism of triose phosphate isomerase

Stage 3 of glcolysis: the oxidation of three-carbon fragments yields ATP -CH2 -C-OH -C=O -COOH

(6) Glyceraldehyde-3-phosphate is Oxidized The energy yielding phase Glyceraldehyde 3-phosphate DH 甘油醛-3-磷酸脱氢酶，GAPDH 1，3二磷酸甘油酸 ΔG°’ = 1.5 kcal mol-1 An aldehyde（醛）is oxidized to carboxylic acid（羧酸） and inorganic phosphate is transferred to form acyl-phosphate（酰基磷酸）. NAD+ is reduced to NADH. 1,3-BPG has a high phosphoryl-transfer potential. It is a mixed anhydride（酐）. Notice, under anaerobic conditions NAD+ must be re-supplied.

(6) Glyceraldehyde-3-phosphate is Oxidized GAPDH反应机制 1，3二磷酸甘油酸 ~ 甘油醛-3-磷酸 ∆G0’ = - 43.1 kJ/mol ∆G0’ = 49.4 kJ/mol

(6) Glyceraldehyde-3-phosphate is Oxidized 甘油醛-3-磷酸脱氢酶 The active site includes a Cys and His adjacent to a bound NAD+ GAPDH 碘乙酸 无活性的酶

(6) Glyceraldehyde-3-phosphate is Oxidized 甘油醛-3-磷酸脱氢酶（GAPDH）能够利用砷酸代替磷酸参加反应，生成3-P-甘油酰砷酸，这是一个高度不稳定的化合物， 在水溶液中，可立刻自发地分解为3-P-甘油酸和砷酸。 因此，砷酸不抑制糖酵解的继续进行，但它不能产生高能磷酸键。所以，砷酸是糖酵解中基质水平磷酸化的解偶联剂。

(7) The anhydride phosphate in 1,3-BPG is used to generate ATP Phosphoglycerate Kinase （磷酸甘油酸激酶，PGK） Substrate-level phosphorylation （ 底物水平的磷酸化） ~ 3-磷酸甘油酸 ΔG°’ = -4.5 kcal mol-1 1，3-二磷酸甘油酸 Remember: 2 molecules of ATP are produced per glucose. At this point 2ADPs were invested and 2ATPs are produced.

Mutase belongs to the isomerase family. (8) Phosphate reversibly shifts between C2 and C3 on glycerate Phosphoglycerate mutase 磷酸甘油酸变位酶 ΔG°’ = 1.1 kcal mol-1 Phosphate shift 3-磷酸甘油酸 2-磷酸甘油酸 Mutase belongs to the isomerase family.

2,3-BPG is Involved in Phosphoglycerate Mutase Action 2,3-bisphosphoglycerate 2，3-二磷酸甘油酸 2，3-BPG 在红细胞对氧的转运中还起着调节剂的作用 A phosphorylation cycle exists. 2,3-bisphosphoglycerate initially phosphorylate the enzyme; It is also an intermediate for 3-PG to be converted to 2-PG;

Catalyzed by enolase, generating phosphoenolpyruvate (磷酸烯醇式丙酮酸，PEP); (9) The Phosphoryl Group Transfer Potential is Markedly Elevated by Dehydration Enolase（烯醇化酶） Dehydration reaction ΔG°’ = 0.4 kcal mol-1 Catalyzed by enolase, generating phosphoenolpyruvate (磷酸烯醇式丙酮酸，PEP); An enolphosphate （烯醇磷酸酯） has high phosphoryl （磷酰基）group transfer potential （高基团转移势能）.

(9) The Phosphoryl Group Transfer Potential is Markedly Elevated by Dehydration 烯醇化酶与底物结合前先与2价阳离子如Mg2+或Mn2+,形成一个复合物,才有活性. 氟与镁和无机磷酸形成一个复合物,取代天然情况下酶分子上镁离子的位置,从而使酶失活. Enolase can be inhibited by F― strongly.

(10) The Phosphate Group on PEP is Transferred to ADP Pyruvate Kinase，丙酮酸激酶 ΔG°’ = -7.5 kcal mol-1 烯醇式 酮式

(10) The Phosphate Group on PEP is Transferred to ADP 2nd example of substrate level phosphorylation. The net yield from glycolysis is 2 ATP. Substrate level phosphorylcation is the synthesis of ATP from ADP that is not linked to the electron transport system（电子传递系统）. PEP+ADPPyr+ATP （底物水平磷酸化）

Summary: ∆G at each step of Glycolysis 标准态 红血球 GlucosePyruvate

Summary: The Conversion of Glucose to Pyruvate Glucose + 2 Pi + 2 ADP + 2 NAD+ → 2 pyruvate + 2 ATP + 2 NADH +2 H+ The Energy released from the anaerobic conversion of glucose to pyruvate is -47 kcal mol-1. Under aerobic conditions much more chemical bond energy can be extracted from pyruvate. The question still remains: How is NAD+ supplied under anaerobic conditions? Or how is redox balance maintained?

2.2.4 Diverse fates of pyruvate ∆G0’ = -25.1 kJ/mol ∆G0’ = -10.46 kJ/mol CO2+H2O Ethanol and lactate can be formed by reactions involving NADH. Alternatively, a two-carbon unit from pyruvate can be coupled to coenzyme to form acetyl CoA.

(1) Pyruvate is the final electron acceptor in lactic acid fermentation Pyruvate reduced (还原) and NAD+ regenerated (生成); Catalyzed by lactate dehydrogenase (乳酸脱氢酶); This happens in animal tissues when O2 is limited; This also happens in many microorganisms (e.g., lactobacilli). What happens after a run?

(2) Acetaldehyde is the final electron acceptor in alcohol fermentation Pyruvate decarboxylase 丙酮酸脱羧酶 (present only in those alcohol fermentative organisms) and alcohol dehydrogenase 乙醇脱氢酶 (present in many organisms including human) catalyzes the two-step reactions. ∆G0’ = -10.46 kJ/mol

Remember! 酵解过程必须提供NAD+，而缺氧的情况下, NADH不能够把H传递给电子传递链而产生NAD+；NADH的H可以选择传递给产物从而使酵解过程得以进行从而产生能量。

2.2.5 Overal balance of glycolysis 碳原子途径（碳骨架的去向）: 2  3C Glucose(6C) 2pyruvate(3C) 2  2C + 2CO2 消耗 G6P 的形成 －1 FBP的形成 －1 产生 1,3-二磷酸甘油酸的形成 + 2 PEP的形成 + 2 磷原子途径 (ATP的变化): 氧化还原反应的电子途径: 1,3-二磷酸甘油酸的形成 2  NADH + H+ 终产物

Overall balance: Glucose + 2ADP + 2Pi + 2NAD+ 2 pyruvate + 2ATP + 2H2O + 2NADH + 2H+ Glucose + 2 ADP + 2Pi 2 lactates + 2ATP + 2H2O + 135.56 kJ/mol Glucose + 2 ADP + 2Pi 2 Ethanol + 2ATP + 2CO2 + 2H2O + 106.27 kJ/mol

2.2.6 Regulation of the Glycolytic pathway The glycolytic pathway is tightly controlled Enzyme reactions that have a significant negative ΔG°’ are often control sites. IN glycolysis: Hexokinase Phosphofuctokinase(PFK) Pyruvate Kinase are regulatory enzymes. PFK is the most important. 磷酸果糖激酶催化的反应是糖酵解的限速反应。

2.2.6.1 PFK is an allosteric enzyme High levels of ATP inhibit, increased levels of AMP reverses the action of ATP. Citrate(柠檬酸） also inhibits PFK. High levels of citrate indicates that the cell is rich in biosynthetic precursors（生物合成前导物） emanating from the pathway. 糖酵解作用不仅是提供能量，也为生物合成提供碳骨架。

2.2.6.1 PFK is an allosteric enzyme 酶分子可逆变构，磷酸化作用调节及转录控制根据不同情况下可在百万之一秒、几秒或几小时内发生变化。

2.2.6.1 PFK is an allosteric enzyme F-1,6-BP + ADP ATP + F-6-P 前馈刺激 PFK2 F-2,6-BP + ADP F-2,6-BP is an allosteric activator, increasing the affinity of PFK for fructose 6-phosphate. Thus, stimulating glycolysis（加速糖酵解）. G多G-6-P多,葡萄糖激酶作用,而G-6-P,则F-6-P多,ATP与F-6-P在PFK2的作用下生成F-2,6-BP Fructose 2,6-bisphosphate （果糖-2，6-二磷酸）activates PFK; it is a positive allosteric effector (激活剂）.

2.2.6.1 PFK is an allosteric enzyme FBPase2 Two Enzymatic Activities Control the levels F-2,6-BP. Phosphofructokinase 2 (PFK-2) catalyzes the formation of F-2,6-BP from F-6P. F-2,6-BP is converted back to F-6P by fructose bisphosphatase 2 (FBPase-2). Both activities are on the same protein. It’s a bifunctional enzyme.

2.2.6.2 Hexokinase also Regulates Glycolysis Hexokinase is inhibited by its product, glucose 6-phosphate. High concentrations of glucose 6-phosphate indicates that the cell no longer needs glucose for energy, for storage as glycogen, or for other precursors. Remember that the liver (肝脏) is responsible for regulating blood glucose levels.

Hexokinase and Glucokinase. 2.2.6.2 Hexokinase also Regulates Glycolysis Hexokinase and Glucokinase. The liver contains an isoform of hexokinase called glucokinase (葡萄糖激酶） Glucokinase is not inhibited by glucose 6-phosphate. Glucokinase has a lower affinity for glucose than hexokinase. This assures that brain and muscle have first choice for the glucose. When glucose is abundant in the liver, glucokinase phosphorylates glucose to glucose 6-phosphate specifically for glycogen synthesis.

2.2.6.3 Pyruvate kinase has regulatory role in glycolysis Pyruvate Kinase has an L (liver) and M (muscle and brain) form. Both forms are inhibited by its product, ATP. Fructose 1,6-bisphosphate activates both forms of the enzyme to keep pace with the influx （流入） on intermediates. 当机体能荷或糖酵解的中间物积累时，丙酮酸激酶达到活跃顶峰。 Alanine (丙氨酸) can be reversibly transaminated (转氨） to pyruvate. Alanine also inhibits pyruvate kinase thus indicating that building blocks are abundant.

Phosphorylation of Pyruvate Kinase When blood-glucose levels are low the glucagon cAMP cascade phosphorylates pyruvate kinase making it less active. This covalent regulation assures that brain and muscle get glucose when needed. Pyruvate kinase: only L-form is regulated by covalent modification.

2.2.7 其它糖进入糖酵解的途径 G0’ = 3.05 kJ/mol 2.2.7 其它糖进入糖酵解的途径 2.2.7.1. Glycogen（糖原） is converted to glucose-1-P by phosphorolysis（磷酸解） G0’ = 3.05 kJ/mol The reaction is a phosphorolysis, not hydrolysis.

2.2.7 其它糖进入糖酵解的途径 Mutase 变位酶 G0’ = -7.28 kJ/mol

2.2.7.2 Fructose(果糖）enters glycolysis mainly via F-1-P pathway 2.2.7 其它糖进入糖酵解的途径 2.2.7.2 Fructose(果糖）enters glycolysis mainly via F-1-P pathway

2.2.7.3 Mannose（甘露糖） enters glycolysis mainly via the Fru-6-P pathway 2.2.7 其它糖进入糖酵解的途径 2.2.7.3 Mannose（甘露糖） enters glycolysis mainly via the Fru-6-P pathway ATP ADP Mannose Mannose-6-phosphate Hexokinase M6P isomerase 异构酶 Fructose-6-phosphate 2位

In adults: Glucose-6-phosphate 2.2.7.4 Galactose （半乳糖） enters glycolysis pathway via the galactose-glucose interconversion pathway （p87-88） 尿苷酰转移酶 ATP ADP Galactose-1-phosphate UDP-Galactose Galactose galactokinase NAD+ NADH 4位 UDP-4-keto-Glucose UTP PPi NADH Glucose-6-phosphate Glucose-1-phosphate NAD+ UDP-Glucose mutase UDP-半乳糖-4-差向异构酶 UDP-Galactose 4-epimerase UDP-葡萄糖焦磷酸化酶 In adults:

In infants: Galactose-1-phosphate Galactose UDP-Glucose UDP-Galactose 2.2.7.4 Galactose enters glycolysis pathway via the galactose-glucose interconversion pathway ADP ATP Galactose-1-phosphate Galactose UDP-Glucose galactokinase NAD+ NADH UDP-4-keto-Glucose Galactose-1-phosphate uridylyl transferase NADH NAD+ Glucose-1-phosphate UDP-Galactose mutase UDP-Galactose 4-epimerase Glucose-6-phosphate In infants:

Entry points in glycolysis for galactose and fructose 双糖及多糖经消化后形成的单糖主要是葡萄糖，其他的单糖产物果糖、半乳糖、甘露糖等，都转变成糖酵解的中间产物之一而进入糖酵解的共同途径。

乳糖 海藻糖 糖原，淀粉 蔗糖 甘露糖

2.2.7 其它糖进入糖酵解的途径 2.2.7.5 Glycerol （甘油） ADP (1) Glycerol + ATP 2.2.7 其它糖进入糖酵解的途径 2.2.7.5 Glycerol （甘油） ADP (1) Glycerol + ATP Glycerol-3-phosphate glycerolkinase NAD+ NADH +H+ (2) Glycerol-3-phosphate Dihydroxyacetonephosphate 二羟基丙酮磷酸

2.2.7 其它糖进入糖酵解的途径 2.2.7.5 Glycerol （甘油） 甘油是前手性分子 DHAP

2.2.8 糖酵解中的能量利用率 纯有机化学反应由葡萄糖生产乳酸： G0’ = -196.56 kJ/mol 2.2.8 糖酵解中的能量利用率 纯有机化学反应由葡萄糖生产乳酸： G0’ = -196.56 kJ/mol 胞内生化反应由葡萄糖生产乳酸： G0’ = -135.6 kJ/mol 差值用于ATP的合成：61 kJ/mol 则能量利用率为： 同理酵母转化葡萄糖为乙醇时的能量利用率：

2.2.8 糖酵解中的能量利用率 注意： 以上能量利用率的计算是按照标准条件下的物质浓度计算的，而在生物细胞中，生化反应中间产物的浓度远远达不到标准状况，根据胞内物质的能量计算，产生1个ATP所固定的能量约为50.2－54.4 kJ/mol，则能量转换率为50％或更高。