Glycogen, Starch, Sucrose
Storage
Pentose phosphate
pathway (oxidation)
Ribose 5-phosphate
Glycolysis
(oxidation)
Pyruvate
Eduard Buchner
(1860-1917)
1897 found fermentation in
broken yeast cells
1907 Nobel Prize in
Chemistry
The whole pathway in yeast and
muscle cell were elucidated by
Arthur Harden
1865-1940
Glycolysis
• Glycolysis is an almost universal central
pathway of glucose catabolism, the
pathway with the largest flux of carbon in
most cells.
• In some mammalian tissues (erythrocytes,
renal medulla, brain, sperm), the
glycolytic breakdown of glucose is the
sole source of metabolic energy.
Glycolysis
• Some of the starch-storing tissues,
like potato tubers, and some aquatic
plants derive most of their energy
from glycolysis.
• Many anaerobic microorganisms are
entirely dependent on glycolysis.
1. phosphorylation of glucose
G 6-P
2. Isomerization of glucose
6-phosphate
G 6-P
F 6-P
3. Phosphorylation of fructose 6phosphate: the first committed
step in glycolysis
F 6-P
F 1,6-BP
4. Cleavage of fructose 1,6bisphosphate
G 3-P
F 1,6-BP
DHAP
5. Interconversion of the
triose phosphate
6. Oxidation of glyceraldehyde 3-phosphate
to 1,3-bisphosphoglycerate
1,3-BPG
7. Phosphoryl transfer from 1,3bisphosphoglycerate to ADP
3-PGA
The formation of ATP by phosphoryl group
transfer from a substrate is referred to as a
substrate-level phosphorylation
Substrate-level phosphorylation
soluble enzymes
chemical intermediates
Respiration-linked phosphorylation
Photophosphorylation
membrane-bound enzymes
transmembrane gradients of protons
Substrate-level phosphorylation
Respiration-linked phosphorylation
or Photophosphorylation
ATP
ADP
H+
H+
Glyceraldehyde 3-phosphate
dehydrogenase and Phosphoglycerate
kinase are coupled in vivo
• Glyceraldehyde 3-phosphate
dehydrogenase catalyzes an
endergonic reaction while
phosphoglycerate kinase catalyzes
an exergonic reaction.
• When these two reactions are
coupled (which happens in vivo), the
overall reaction is exergonic.
Glyceraldehyde 3-phosphate dehydrogenase
G 3-P
1,3-BPG
ATP
NADH3-PGA
Pi
NAD+
ADP
Phosphoglycerate kinase
8. Conversion of 3phosphoglycerate to 2phosphoglycerate
2-PGA
The phosphoglycerate
mutase reaction
The phosphoglycerate mutase
reaction
COO|
HCOH
|
CH2O
2,3-bisphosphoglycerate
3-phosphoglycerate
2-phosphoglycerate
Phosphoglycerate
mutase
9. Dehydration of 2phosphoglycerate to
phosphoenolpyruvate
PEP
10. Transfer of the phosphoryl group
from phosphoenolpyruvate to ADP
Glucose + 2ATP + 2NAD+ + 4ADP + 2Pi

2 pyruvate + 2ADP + 2NADH + 2H+
+ 4ATP + 2H2O
Glucose + 2ADP + 2NAD+ + 2Pi 
2 pyruvate + 2ATP + 2NADH + 2H+
在有氧狀況下，產生的NADH很快就被送
到mitochondria中用來合成ATP
Pyruvate
pyruvate
ATP
ATP
kinase
glucose
ATP
Hexokinase
ADP
G
6-P
Mg2+
PEP
2-PGA
PhosphoGlycerate
2-PGA
mutase Mg2+
Phosphohexose
F 6-P
isomerase Mg2+
ATP
FPFK-1
1,6-BP
ADP Mg2+
F 1,6-BP
ADP
enolase
H
O
PEP
2
2
G 6-P
F 6-P
Mg2+
Pi
NAD+
3-PGA
PhosphoGlyceraldehyde
glycerate
NADH
aldolase
G
3-P
G
3-P
NADH
3-PGA
ATP
DHAP
1,3-BPG
1,3-BPG
3-phosphate
+
kinase Mg2+
+
+
H
+
H
dehydrogenase
Triose
ADP
Phosphate
G
3-P
DHAP
isomerase
NAD+ (nicotinamide adenine
dinucleotide) is the active form of
niacin
Niacin (Vitamin B3)
• Niacin is the common
name for
nicotinamide and
nicotinic acid.
• Nicotinic acid is the
common precursor
for NAD+ and NADP+
biosynthesis in
cytosol.
Functions of NAD+ and
+
NADP
• Both NAD+ and NADP+ are
coenzymes for many
dehydrogenases in cytosol and
mitochondria
• NAD+ is involved in oxidoreduction
reactions in oxidative pathways.
• NADP+ is involved mostly in
reductive biosynthesis.
Niacin deficiency: pellagra
Weight loss, digestive disorders, dermatitis, dementia
Niacin deficiency
• Because niacin is present in most of the food
and NAD+ can also be produced from tryptophan
(60 grams of trptophan  1 gram of NAD+), so it
is not often to observe niacin deficiency.
• However, niacin deficiency can still be observed
in areas where maize is the main carbohydrate
source because maize only contain niacytin, a
bound unavailable form of niacin. Pre-treated
maize with base will release the niacin from
niacytin.
Niacin deficiency
• Areas where sorghum is the main carbohydrate
source will also observe niacin deficiency if
niacin uptake is not being watched carefully.
• Sorghum contains large amount of leucine,
which will inhibit quinolinate phosphoribosyl
transferase (QPRT), an enzyme involved in NAD+
biosynthesis from tryptophan.
• Vitamin B6 deficiency can also lead to niacin
deficiency because pyridoxal phosphate is a
coenzyme in NAD+ biosynthesis from tryptophan.
Feeder pathways for glycolysis
p.535
p.535
Stored glycogen and starch are
degraded by phosphorolysis
• Glycogen and starch can be mobilized for
use by a phosphorolytic reaction
catalyzed by glycogen/starch
phosphorylase. This enzyme catalyze an
attack by Pi on the (a14) glycosidic
linkage from the nonreducing end,
generating glucose 1-phosphate and a
polymer one glucose unit shorter.
p.536
Branch point (a16) is removedp.536
by debranching enzyme
a-1,6 glucosidase
Transferase
activity
activity
of
of
Debranching enzyme
P
P
P
P
P
phosphorylase
P
P
P
p.535
Digestion of dietary
polysaccharides
• Digestion begins in the mouth with
salivary a-amylase hydrolyze (attacking
by water) the internal glycosidic linkages.
• Salivary a-amylase is then inactivated by
gastric juice; however pancreatic aamylase will take its place at small
intestine.
• The products are maltose, maltotriose,
and limit dextrins (fragments of
amylopectin containing a16 branch
points.
Endo (a-amylase) and exo enzymes
p.535
Digestion of dietary
disaccharides
• Disaccharides must be hydrolyzed to
monosaccharides before entering cells.
dextrinase
• Dextrin + nH2O  n D-glucose
maltase
• Maltose + H2O  2 D-glucose
lactase
• Lactose + H2O  D-galactose + D-glucose
sucrase
• Sucrose + H2O  D-fructose + D-glucose
trehalase
• Trehalose + H2O  2 D-glucose
p.535-6
Lactose intolerance
• Lactose intolerance is due to the
disappearance after childhood of most or
all of the lactase activity of the intestinal
cells.
p.535-6
Lactose intolerance
• Undigested
lactose will be
converted to toxic
products by
bacteria in large
intestine, causing
abdominal cramps
and diarrhea.
p.536
Fructose metabolism in
muscle and kidney
Fructose
Mg2+
hexokinase
FADP
6-P
F 6-P
ATP
ATP
F 1,6-BP
2 4NADH
ATP
Glycolysis
F PFK-1
1,6-BP
ADP
p.536
Fructose metabolism in liver
Mg2+
Fructose
ATP
fructokinase
FADP
1-P
F 1-P
DHAP
Triose
G 3-P
phosphate
isomerase
Fructose
DHAP
glyceraldehyde
1-phosphate
aldolase
Mg2+
Triose
G
ADP
3-P
kinase
glyceraldehyde
ATP
ATP
Galactose metabolism
(p.536,537)
galactose
Mg2+
galactokinase
Gal
ADP
1-P
UDP-glucose
+
UDP-Glc
NAD
NADH
4-epimerase
Gal 1-P
UDP-glucose:
UDP-Gal Galactose
UDP-Gal
G 1-P1-P
uridylyltransferase
NADH NAD+
UDP-Glc
• Galactose is phosphorylated by galactokinase in
the liver.
• Then galactose 1-phosphate is converted to
glucose 1-phosphate by a series of reactions.
Epimer and epimerase (p. 241)
• Two sugars that differ only in the
configuration around one carbon atom are
called epimers.
• Enzymes that catalyze inversion of the
configuration about an asymmetric carbon
in a substrate having more than one center
of asymmetry are called epimerases.
D-Mannose is a C2-epimer of D-glucose
1 CHO
|
HO-C-H
|
3
HO-C-H
|
4
H-C-OH
|
5
H-C-OH
|
6 CH2OH
2
D- mannose
1CHO
|
2
H-C-OH
|
3
HO-C-H
|
4
H-C-OH
5|
H-C-OH
|
6
CH2OH
D- glucose
p.537
Galactosemia
inability to metabolize galactose due to lack
of
1. UDP-glucose galactose 1-phosphate
uridylyltransferase (classical
galactosemia)
2. UDP-glucose 4-epimerase
3. Galactokinase
Among these, deficiency of either 1 or 2 is
more severe (1 is the most severe).
p.537
Galactosemia
• Deficiency of
transferase (or
epimerase) will result
in poor growth,
speech abnormality,
mental deficiency,
and (fatal) liver
damage even when
galactose is withheld
from the diet.
p.537
Mannose metabolism
mannose
Mg2+
Hexokinase
Man
ADP
6-P
ATP
Man 6-P
Phosphomannose
F 6-P
isomerase
p.538
Fermentation
• Fermentation is referring to the
process when no oxygen is
consumed or no change in the
concentration of NAD+ or NADH
during energy extraction.
Fermentation
• Under hypoxic conditions, oxidative
phosphorylation will be the first to stop. Then
citric acid cycle will come to a halt due to
inhibition effect from NADH. As a result,
glycolysis will be the only metabolic pathway that
is available to energy production during hypoxia.
2 ADP
Glucose
2 NAD+
Fermentation
2 2pyruvate
Glycolysis
2NADH
ATP
2 acetyl-CoA
22PDH
NADH
CO2
2 Acetyl-CoA
2 NADH 2 NAD+ 2 NADH
Oxidative
+
2 FAD
NAD
n
ATP
phosphorylation 6 NADH
2 FADH2
n ADP
Citric
NADH
CO
Acid
264
2FADH
ATP2 2
cycle
6 NAD+
• However, the oxidation of glyceraldehyde 3phosphate consumes NAD+ that will not be
regenerated under hypoxic condition because
oxidative phosphorylation is not available.
2 FAD
2 ADP
The purpose of fermentation is
to regenerate NAD+
2 ADP
• In order to continue
regenerating NAD+,
cells come up a
2 NAD+
strategy.
2 NADH
2 pyruvate • During fermentation,
NAD+ is regenerated
fermentation
22lactate
NAD+
during the reduction
of pyruvate, the
product of glycolysis.
glucose
2glycolysis
2pyruvate
2NADH
ATP
Lactate fermentation
glycolysis
Lactate is being recycled in
liver (Cori cycle)
liver
muscle
glucose
6 ATP 2 pyruvate
2 lactate
glucose
2ATP
2 pyruvate
2 lactate
Carl and Gerty Cori, 1947 Nobel Prize in Physiology and
Medicine
Lactate fermentation only
happened in larger animals
• Most small
vertebrates and
moderate size
running animals have
circulatory systems
that can carry oxygen
to their muscles fast
enough to avoid
having to use muscle
glycogen
anaerobically.
http://www.mountain-research.org/CV/coelacanth.jpg
http://www.anac.8m.net/Images/coelacanth.jpg
Deep sea fish (below 4,000
m or more) coelacanth uses
anaerobic metabolism
exclusively. The lactate
produced is excreted
directly. Some marine
vertebrates can do ethanol
fermentation.
Ethanol fermentation
• Yeast and other microorganisms ferment glucose
to ethanol and CO2.
• Pyruvate is first decarboxylated by pyruvate
decarboxylase, which is absent in vertebrate
tissues and in other organisms that carry out
lactic acid fermentation. Acetaldehyde is the
product of this reaction.
Pyruvate decarboxylase
• The
decarboxylation of
pyruvate by
pyruvate
decarboxylase
produces CO2,
which is the
reason why
champagne is
bubbling.
Thiamine pyrophosphate (TPP) is
the coenzyme of pyruvate
decarboxylase
• Thiamine pyrophosphate is derived from vitamin
B1 (thiamine).
• Lack of vitamine B1 will lead to beriberi (edema,
pain, paralysis, death; Singhalese “I cannot”
Signifying the person is too ill to do anything.).
Alcohol dehydrogenase catalyze
the second step of ethanol
fermentation
• Alcohol
dehydrogeanse
reduces
acetaldehyde,
producing NAD+
and ethanol.
• This enzyme is
present in many
organisms that
metabolize ethanol,
including human.
Fermentation has
commercial values
• Bacteria like
Lactobacillus
bulgaricus (yogurt)
and
Propionibacterium
freudenreichii
(swiss cheese)
ferments milk to
produce lactic
acid or propionic
acid and CO2.
Dr. Chaim Weizmann
1874-1952
First President of Israel
Found butanol and acetone
fermentation in Clostridium acetobutyricum
Industrial fermentation is
done in huge close vats
• Fermentors are huge
closed vats in which
temperature and
access to air are
adjusted to favor the
multiplication of the
desired microorganism.
• Some even immobilize
the cells in an inert
support so no effort is
required to separate
microorganisms from
products after
fermentation is
completed.