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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
2. Isomerization of glucose 6phosphate
Phosphohexose isomerase reaction
by an active-site His residue
Glu
3. Phosphorylation of fructose 6phosphate: the first committed step
in glycolysis
PFK-1 is named so because there
is another enzyme catalyzes a
similar reaction
In some bacteria, protists and (all) plants,
a pyrophosphate-dependent
phosphofructokinase (PFP) also
catalyzes this reaction in a reversible
way
4. Cleavage of fructose 1,6bisphosphate
Class I aldolases form Schiff base
intermediate during sugar cleavage reaction
• Class I aldolases were
found in animals and
plants.
• Class II aldolases
(fungi and bacteria) do
not form the Schiff
base and require a zinc
ion to catalyze
reaction.
5. Interconversion of the triose
phosphate
Dihydroxyacetone phosphate and
glyceraldehyde 3-phosphate become
indistinguishable after triose phosphate
isomerase reaction
6. Oxidation of glyceraldehyde 3phosphate to 1,3-bisphosphoglycerate
The glyceraldehyde 3-phosphate
dehydrogenase reaction
Heavy metal ion
such as Hg2+ will
react with Cys
residue, hence
irreversibly
inhibits the
enzyme.
hemiacetal
7. Phosphoryl transfer from 1,3bisphosphoglycerate to ADP
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.
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
8. Conversion of 3phosphoglycerate to 2phosphoglycerate
The phosphoglycerate mutase
reaction
2,3-Bisphosphoglycerate (BPG)
• The concentration of
BPG is usually low in
most of the tissues
except erythrocytes
(up to 5 mM).
• Function of BPG in
erythrocytes is to
regulate the affinity of
hemoglobulin to O2.
9. Dehydration of 2phosphoglycerate to
phosphoenolpyruvate
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
NAD+ (nicotinamide adenine
dinucleotide) is the active form of
niacin
Niacin
• 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.
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Feeder pathways for glycolysis
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 1phosphate and a polymer one glucose unit
shorter.
Branch point (a16) is removed
by debranching enzyme
Glucose 1-phosphate is converted to G-6-P by
phosphoglucomutase by the same mechanism
observed in phosphoglycerate mutase reaction
Digestion of dietary
polysaccharides
• Digestion begins in the mouth with salivary aamylase hydrolyze (attacking by water) the
internal glycosidic linkages.
• Salivary a-amylase is then inactivated by gastric
juice; however pancreatic a-amylase will take its
place at small intestine.
• The products are maltose, maltotriose, and limit
dextrins (fragments of amylopectin containing
a16 branch points.
Digestion of dietary
disaccharides
• Disaccharides must be hydrolyzed to
monosaccharides before entering cells.
• Dextrin + nH2O  n D-glucose
dextrinase
• Maltose + H2Omaltase
 2 D-glucose
• Lactose + H2Olactase
 D-galactose + D-glucose
• Sucrose + H2Osucrase
 D-fructose + D-glucose
• Trehalose + H2Otrehalase
 2 D-glucose
Lactose intolerance
• Lactose intolerance is due to the disappearance
after childhood of most or all of the lactase
activity of the intestinal cells.
Lactose intolerance
• Undigested lactose
will be converted to
toxic products by
bacteria in large
intestine, causing
abdominal cramps and
diarrhea.
Fructose metabolism in muscle
and kidney
Fructose metabolism in liver
Triose
phosphate
isomerase
• In liver, the enzyme fructokinase
catalyze the phosphorylation of fructose to form
fructose 1-phosphate.
Galactose metabolism
• Galactose is phosphorylated by galactokinase in
the liver.
• Then galactose 1-phosphate is converted to
glucose 1-phosphate by a series of reactions.
Galactose metabolism
• The conversion of galactose
1-P to glucose 1-P
(epimerization) requires
uridine diphosphate (UDP)
as a coenzyme-like carrier of
hexose groups.
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).
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.
Galactosemia patients develop cataracts
by deposition of galactitol in the lens
Mannose metabolism
Mannose + ATP  mannose 6-phosphate
hexokinase
+ADP
mannose 6-phosphate  fructose 6-phosphate
phosphomannose isomerase
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.
Fermenation
• However, the
oxidation of
glyceraldehyde 3phosphate consumes
NAD+ that will not be
regenerated under
hypoxic condition
because oxidative
phosphorylation is not
available.
The purpose of fermentation is to
regenerate NAD+
• In order to continue
regenerating NAD+,
cells come up a
strategy.
• During fermentation,
NAD+ is regenerated
during the reduction of
pyruvate, the product
of glycolysis.
Lactate fermentation
glycolysis
Lactate is recycled in the liver
(Cori cycle)
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).
TPP plays an important role in the cleavage of
bonds adjacent to a carbonyl group.
• The thiazolium ring of
TPP acts as an
“electron sink” to
facilitates
decarboxylation
reaction.
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.