Transcript 03-1 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
a-淀粉酶
b-淀粉酶
淀粉酶
多糖水解酶
纤维素酶
半纤维素酶
果胶酶
糖苷水解酶
葡萄糖淀粉酶
麦芽糖酶
蔗糖酶
乳糖酶
●
●
●
异淀粉酶
1.2 糖类在人体中的消化
糖类食物
唾液淀粉酶
咀嚼、部分水解
第一
阶段
HCl
有限水解
胰淀粉酶
a-糊精、麦芽糖和少量葡萄糖
第二
阶段
糖苷酶
单糖
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
糖的吸收方式
促进扩散
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
GlycolysisDerived 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”.
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-1phosphate;
 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
1.
The glycolysis is a pathway from glucose to pyruvate;
葡萄糖
Yeast
丙酮酸
The fate of glucose is
varies with physiological
conditions, tissues, and
organisms.
Exercising
muscle
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；
碳原子途径
磷酸途径
氧化还原反应的电子途径
7. Glycolysis is highly regulated.
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 )
2.2.2 Overview of glycolysis
8. Types of reactions occurring in glycolysis
Phosphoryl group transfer: kinase(激酶);
O
R
OH
+
ATP
Kinase
R
O
P
O-
+
ADP
O-
激酶
A
C
B
磷酸化酶
D
+
H+
2.2.2 Overview of glycolysis
8. Types of reactions occurring in glycolysis
Phosphoryl group shift: mutase（变位酶）
O-O
OH
C
H
CH
2
O
P
O-
O
O
O
Mutase
R
P
O-
R
C
CH
2
OH
H
Phosphoryl shift. A phosphoryl group is shifted
from one oxygen atom to another within a molecule
by a mutase.
2.2.2 Overview of glycolysis
8. Types of reactions occurring in glycolysis
Isomerization: isomerase(异构酶);
O
CH2OH
C
R
O
Isomerase
H
C
H
C
OH
R
Isomerization. A ketose (酮糖） is converted into
an aldose （醛醣）, or vice versa, by an isomerase.
2.2.2 Overview of glycolysis
8. Types of reactions occurring in glycolysis
Dehydration: dehydratase（enolase, 烯醇化酶）
H
H
C
C
H
C
OH
Dehydratase
H
C
+H2O
H
Dehydration. A molecule of water is eliminated by
a dehydratase.
2.2.2 Overview of glycolysis
8. Types of reactions occurring in glycolysis
Aldol cleavage: aldolase（醛缩酶）
R
R
C
O
HO
C
H
H
C
OH
R'
Aldolase
HO
C
O
C
H
H
H
C
O
R'
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-3phosphate
Payoff phase
Conversion of
glyceraldehyde-3phosphate 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+
O-
ÏÙÜÕ-O
P
O-
-O
O
P
H
O
P
O
O
O
a
b

O
CH2
O
O-
OH
OH
OH
OH
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
同工酶
性质
Ⅰ
Ⅱ
Ⅲ
Ⅳ
（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
100
100
5-6.8
km(mM葡萄糖)
0.05
0.2
0.007
12
km(mM果糖)
3
3
3
 800
VG(μM/min·ng pr.)
80
VF / VG
1.1
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
＋
40
－
(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
ADP
F6P
cAMP
K+
ATP
Citrate
PEP
phosphocreatine
3PG（甘油酸）
NH4+
PO43-
2PG （甘油酸）
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）
(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
二羟丙酮磷酸
（DHAP）
单烯二羟负
离子中间体
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 3carbon 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 acylphosphate（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
1，3-二磷酸甘油酸
ΔG°’ = -4.5 kcal mol-1
Remember: 2 molecules of ATP are produced per glucose.
At this point 2ADPs were invested and 2ATPs are produced.
(8) Phosphate reversibly shifts between C2 and C3 on glycerate
Phosphoglycerate mutase
磷酸甘油酸变位酶
Phosphate shift
3-磷酸甘油酸
ΔG°’ = 1.1 kcal mol-1
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
• 2,3-bisphosphoglycerate initially phosphorylate the enzyme;
• It is also an intermediate for 3-PG to be converted to 2-PG;
(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)

磷原子途径
2pyruvate(3C)
消耗
G6P 的形成 －1
FBP的形成
(ATP的变化):
产生
2  2C + 2CO2
－1
1,3-二磷酸甘油酸的形成 + 2
PEP的形成 + 2

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
PFK1
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 6phosphate. Thus, stimulating
glycolysis（加速糖酵解）.
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



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).
PFK2
FBPase2
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.
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
Pyruvate kinase: only L-form is regulated by covalent modification.
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 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 其它糖进入糖酵解的途径
2.2.7.3 Mannose（甘露糖） enters glycolysis mainly via the Fru6-P pathway
ATP ADP
Mannose-6-phosphate
Hexokinase
M6P
isomerase
Mannose
异构酶
Fructose-6-phosphate
2位
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-
Galactose
galactokinase
UDP-Galactose
phosphate
4位
NAD
+
NADH
UTP
PPi
UDP-4-ketoGlucose
NADH
Glucose-6phosphate
mutase
NAD+
Glucose-1phosphate
UDP-Glucose
UDP-葡萄糖
焦磷酸化酶

In adults:
UDP-半乳糖-4差向异构酶
UDP-Galactose
4-epimerase
2.2.7.4 Galactose enters glycolysis pathway via the galactoseglucose interconversion pathway
ATP
ADP
Galactose-1Galactose
phosphate
galactokinase
Galactose-1-phosphate
uridylyl transferase
UDP-Glucose
NAD
+
NADH
UDP-4-ketoGlucose
NADH
Glucose-1-phosphate
mutase
Glucose-6-phosphate

In infants:
NAD+
UDP-Galactose
UDP-Galactose
4-epimerase
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。
海藻糖
乳糖
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
Glycerol-3-phosphate
glycerolkinase
NAD+
(2) Glycerol-3-phosphate
NADH +H+
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
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：
61
 31 %
196 .56
61
 36 .5%
167 .32
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。