Glycolysis and Gluconeogenesis and PFK-2/FBPase-2 enzyme

1. 1
Glycolysis

2. 2
• Glycolysis can be defined as the sequence of reactions for the breakdown of Glucose (6-carbon
molecule) to two molecules of pyruvic acid (3-carbon molecule) under aerobic conditions; or
lactate under anaerobic conditions along with the production of small amount of energy.
• In organisms that perform cellular respiration, glycolysis is the first stage of this process.
• However, glycolysis doesn’t require oxygen, and many anaerobic organisms that do not use
oxygen—also have this pathway.
• When animal tissues cannot be supplied with sufficient oxygen to support aerobic oxidation of
the pyruvate and NADH produced in glycolysis, NAD+ is regenerated from NADH by the
reduction of pyruvate to lactate.
- Some tissues and cell types (such as
erythrocytes, which have no mitochondria
and thus cannot oxidize pyruvate to CO2)
produce lactate from glucose even under
aerobic conditions.
- The reduction of pyruvate is catalyzed
by lactate dehydrogenase.
• Glycolysis takes place in the cytosol of a cell (cytoplasm).
Steps in Details: https://laboratoryinfo.com/glycolysis-steps-diagram-energy-yield-and-
significance/
1. ○ Most of the reactions of the glycolytic pathway are reversible, which are also used
for gluconeogenesis.
♦There are two types of
glycolysis.
♣Aerobic Glycolysis: It occurs
when oxygen is plentiful.
- Final product
is pyruvate along with the
production of Eight ATP
molecules.
♣Anaerobic Glycolysis: It
occurs when oxygen is scarce.
- Final product is lactate along
with the production of two
ATP molecules.

3. 3
Gluconeogenesis
• Gluconeogenesis (abbreviated GNG) is a metabolic pathway that results in the generation of
glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino
acids.
• It is one of the two main
mechanisms humans and
many other animals use to
keep blood glucose levels
from dropping too low
(hypoglycemia).
• The other means of
maintaining blood
glucose levels is through
the degradation of
glycogen
(glycogenolysis).
• Gluconeogenesis is a
ubiquitous process,
present in plants, animals,
fungi, bacteria, and other
microorganisms.
• In animals,
gluconeogenesis takes
place mainly in the liver
and, to a lesser extent, in
the cortex of kidneys.
• This process occurs
during periods of fasting,
starvation, low-
carbohydrate diets, or
intense exercise and is
highly endergonic.
• Gluconeogenesis is the
reverse process of
glycolysis.

4. 4
• The net production of glucose via gluconeogenesis involves the orchestrated activities of several
key enzymes (pyruvate carboxylase, PEPCK(Phosphoenolpyruvate carboxykinase), aldolase,
fructose-1,6-diphosphatase, and glucose-6-phosphatase)
• Alanine and lactate are Precursors for Gluconeogenesis.
• lactate by lactate dehydrogenase form pyruvate.
• glycogen by glucokinase or hexokinase it form glucose-6-phosphate and then converted to
glucose-1-phosphate by phosphoglucomutase .
- glucose-1-phosphate by a reverse reaction (by phosphoglucomutase) can form glucose-6-
phosphate and enter Gluconeogenesis process .
• Triglyceride by lipolysis turn to glycerol and fatty acids , then glycerol by glycerol kinase form
glycerol -3-phosphate the converted to DHAP and enter Gluconeogenesis process.
• Pyruvate can convert to Oxaloacetate through Kreb’s cycle, or directly by pyruvate carboxylase ,
Then OAA by PEPCK (Phosphoenolpyruvate carboxykinase) it converted to PEP
(Phosphoenolpyruvate) then enter Gluconeogenesis process.
‫اول‬4‫زياده‬ ‫صفح‬‫جدا‬ ‫مهمين‬ ‫بس‬‫منين‬ ‫جه‬ ‫جاي‬ ‫اللي‬ ‫كل‬ ‫نفهم‬ ‫عشان‬‫قالهم‬ ‫الدكتور‬ ‫منهم‬ ‫وفي‬

5. 5
Carbohydrate Metabolism:
Gluconeogenesis,
Reciprocal Regulation
The dual function enzyme PFK-2/FBPase-2 (Key enzyme responsible for
gluconeogenesis and glycolysis) controls flux through gluconeogenesis and
glycolysis by controlling levels of F-2,6-BP in the cell
Key Concepts: Gluconeogenesis
• The importance of gluconeogenesis is to provide glucose for cells from
non-carbohydrate precursors.
• Three steps in glycolysis must be bypassed by gluconeogenic enzymes
in order to overcome large G differences.
• Reciprocal regulation at the PFK-1 (glycolysis) and F-1,6-BPase
(gluconeogenesis) is controlled by the allosteric regulator F-2,6-
bisphosphate, as well as, energy charge (ATP/AMP), and citrate levels.
• The Cori Cycle recycles lactate produced in anaerobic muscle cells
during exercise by exporting it to the liver where it is converted to
pyruvate and used to synthesize glucose by gluconeogenesis.

6. 6
◘Gluconeogenesis and
glycolysis are opposing
pathways:
• Two of the bypass
enzymes in
gluconeogenesis, fructose-
1,6-bisphosphatase-1
(FBPase-1) and glucose-6-
phosphatase, simply
reverse the reaction
However, 4 extra
ATP/GTP, and pyruvate
carboxylase and
phosphoenolypyruvate
carboxykinase (PEPCK),
are required to catalyze the
bypass reaction that
converts pyruvate to PEP.
How do you come up with
the 4 extra ATP/GTP for
gluconeogenesis compared
to glycolysis?

7. 7
♦ Reciprocal regulation of PFK-1 and FBPase-1
The activities of PFK-1 and FBPase-1 are regulated by the allosteric
effectors AMP, citrate, and fructose-2,6-bisphosphate (F-2,6-BP), but in a
reciprocal manner.
‫ال‬ ‫ان‬ ‫عارفين‬ ‫احنا‬ ‫ما‬ ‫زي‬PFK-1‫ال‬ ‫هو‬ ‫اللي‬Phospho-fructo Kinase-1‫ال‬ ‫بيحولي‬
Fructose-6-p‫ل‬Fructose 1,6-bisp‫وال‬glycolysis‫الجلوكوز‬ ‫تكسر‬ ‫عشان‬ ‫طريقها‬ ‫في‬ ‫بتمشي‬
‫ال‬ ‫انزيم‬ ‫عندي‬ ‫والعكس‬FBPase‫هو‬ ‫اللي‬Fructose 1,6-bisphosphatase‫ال‬ ‫ال‬ ‫بيحولي‬Fructose 1,6-bisp‫ل‬Fructose-6-p
‫ال‬ ‫وعمليه‬gluconeogenesis‫جلوكوز‬ ‫تكونلي‬ ‫عشان‬ ‫بتتم‬
‫عار‬ ‫احنا‬ ‫ما‬ ‫زي‬ ‫طيب‬‫ال‬ ‫عمليه‬ ‫ان‬ ‫فين‬glycolysis‫صح‬ ‫طاقه‬ ‫عنها‬ ‫بينتج‬..‫عندي‬ ‫بيبقي‬ ‫يعني‬ATP‫كتير‬!!.
‫ال‬ ‫ان‬ ‫عارفها‬ ‫اكون‬ ‫معلومه‬ ‫في‬ ‫طيب‬ATP‫ل‬ ‫بتتكسر‬AMP‫و‬2P‫ال‬ ‫تركيز‬ ‫ما‬ ‫كل‬ ‫يعني‬AMP‫ال‬ ‫ان‬ ‫ذلك‬ ‫معني‬ ‫يزيد‬ATP‫وقلت‬ ‫استهلكت‬..
‫عندي‬ ‫يكون‬ ‫لما‬ ‫يعني‬AMP‫ال‬ ‫اكون‬ ‫عايز‬ ‫طاقه‬ ‫عايز‬ ‫كدا‬ ‫انا‬ATP‫ال‬ ‫اكون‬ ‫عشان‬ ‫الجلوكوز‬ ‫اكسر‬ ‫وعايز‬ATP‫ال‬ ‫عمليه‬ ‫اعمل‬ ‫عايز‬ ‫يعني‬
glycolysis‫؟‬ ‫صح‬
‫ال‬ ‫كدا‬ ‫يبقي‬AMP‫عمل‬ ‫زاد‬ ‫لما‬ ‫تركيزه‬stimulation‫لل‬PFK-1‫لل‬ ‫طريقه‬ ‫في‬ ‫يكمل‬ ‫عشان‬glycolysis
‫عندي‬ ‫انا‬ ‫لو‬ ‫طيب‬Citrate‫ال‬ ‫في‬ ‫اتكون‬ ‫هو‬ ‫اللي‬ ‫كتير‬Kreb’s cycle‫ال‬ ‫بعد‬ ‫بتحصل‬ ‫اللي‬glycolysis‫عملت‬ ‫انا‬ ‫كدا‬ ‫يبقي‬kreb’s cycle
‫طاقه‬ ‫وعندي‬ATP‫اعمل‬ ‫اني‬ ‫محتاج‬ ‫فمش‬ ‫كتير‬glycolysis‫ال‬ ‫تركيز‬ ‫فبالتالي‬ ‫الجلوكوز‬ ‫في‬ ‫واكسر‬citrate‫يعمل‬Inhibition‫لل‬PFK-1
‫ال‬ ‫عمليه‬ ‫في‬ ‫هنعكسه‬ ‫دا‬ ‫الكالم‬ ‫وطبعا‬gluconeogenesis‫عندي‬ ‫لو‬ ‫ان‬AMP‫كتير‬‫عندي‬ ‫انا‬ ‫يبقي‬ATP‫محتاج‬ ‫مش‬ ‫انا‬ ‫ساعتها‬ ‫يبقي‬ ‫قليل‬
‫ال‬ ‫فبالتالي‬ ‫بيه‬ ‫هحتفظ‬ ‫انا‬ ‫ال‬ ‫الجلوكوز‬ ‫في‬ ‫اكسر‬AMP‫هيعمل‬ ‫هنا‬Inhibition‫لل‬FBPase-1‫وهيبقي‬stimulate‫لل‬PFK-1‫ال‬ ‫لو‬ ‫اما‬
Citrate‫الجلوكوز‬ ‫في‬ ‫اكسر‬ ‫محتاج‬ ‫مش‬ ‫انا‬ ‫يبقي‬ ‫كتير‬ ‫عندي‬..‫ال‬ ‫هعمل‬ ‫فبالتالي‬gluconeogenesis‫ال‬ ‫في‬ ‫اكسره‬ ‫ما‬ ‫بدل‬ ‫الجلوكوز‬ ‫في‬ ‫وهكون‬
glycolysis
‫ال‬ ‫ان‬ ‫عارفها‬ ‫اكون‬ ‫معلومه‬ ‫وفي‬fructose-2,6-bisphosphate‫بيعمل‬ ‫بيتكون‬ ‫لما‬Inhibition‫لل‬Fructose 1,6-bisphosphatase‫ودا‬
‫بعدين‬ ‫عنه‬ ‫هنتكلم‬
What is the metabolic logic of reciprocal regulation by citrate?

8. 8
• In muscle during exercise, AMP levels are high due to consumption of ATP, so
muscle need more ATP by glycolysis.
- High amount of AMP stimulate PFK-1 that stimulate glycolysis.
• When ATP & Citrate are high
- Cells don’t need ATP, so no need for glycolysis.
- High amount of citrate indicate that adequate amount of substrate enter TCA
cycle, so gluconeogenesis is activated
Levels of F-2,6-BP in the cell are controlled by a dual function enzyme called
PFK-2/FBPase-2
• The amount of F-2,6-BP in the cell is controlled by the activity of a dual function
enzyme containing two catalytic activities,
1) a kinase activity called phosphofructokinase-2
(PFK-2) that phosphorylates fructose-6P to form F-
2,6-BP, and
2) a phosphatase activity called fructose-2,6-
bisphosphatase (FBPase-2) that dephosphorylates
F-2,6-BP to form fructose-6P.
‫ال‬ ‫كميه‬F-2,6-BP‫بتعمل‬ ‫انها‬ ‫كدا‬ ‫قبل‬ ‫قولت‬ ‫اللي‬Inhibition‫لل‬Fructose 1,6-
bisphosphatase‫ال‬ ‫عمليه‬ ‫بتوقفلي‬ ‫يعني‬gluconeogenesis‫اصال‬ ‫امتي‬ ‫انا‬ ‫طب‬
‫ال‬ ‫اعمل‬ ‫بحتاج‬gluconeogenesis‫صح‬ ‫اكسره‬ ‫مش‬ ‫جلوكوووز‬ ‫اكون‬ ‫عايز‬ ‫ارفعه‬ ‫عايز‬ ‫وانا‬ ‫الدم‬ ‫في‬ ‫منخفض‬ ‫يكون‬ ‫السكر‬ ‫لما‬ ‫؟؟‬ ‫ايه‬ ‫لما‬..‫؟؟‬..
‫صح‬..‫معاك‬ ‫دي‬ ‫المعلومه‬ ‫خلي‬ ‫تمام‬..
‫اسمه‬ ‫واحد‬ ‫جزئين‬ ‫من‬ ‫متكون‬ ‫انزيم‬ ‫في‬ ‫الوقتي‬PFK-2‫اسمه‬ ‫وواحد‬FBPase-2..
‫ال‬PFK-2‫ال‬ ‫بيحولي‬fructose-6P‫ل‬F-2,6-BP‫ال‬ ‫اتكون‬ ‫ما‬ ‫وبعد‬F-2,6-BP‫ال‬ ‫هو‬ ‫اللي‬ ‫االنزيم‬ ‫من‬ ‫التاني‬ ‫الجزء‬ ‫يجي‬FBPase-2‫يحولي‬
‫ال‬F-2,6-BP‫ل‬fructose-6P
‫؟‬ ‫كدا‬ ‫حلو‬
‫ال‬ ‫تركيز‬ ‫كدا‬ ‫يعني‬F-2,6-BP‫عامل‬Inhibition‫لل‬Fructose 1,6-bisphosphatase‫ال‬ ‫ومانع‬gluconeogenesis‫دا‬ ‫كدا‬ ‫بس‬ ‫مش‬
‫عامل‬ ‫كمان‬Stimulation‫لل‬PFK-1‫ال‬ ‫عمليه‬ ‫في‬ ‫هيساعد‬ ‫اللي‬glycolysis.
‫عمليه‬ ‫واعمل‬ ‫الدم‬ ‫في‬ ‫السكر‬ ‫مستوي‬ ‫ارفع‬ ‫عايز‬ ‫يعني‬ ‫اكسره‬ ‫مش‬ ‫جلوكوز‬ ‫اكون‬ ‫وعايز‬ ‫عندي‬ ‫انخفض‬ ‫والسكر‬ ‫مشكله‬ ‫عندي‬ ‫لو‬ ‫الوقتي‬ ‫انا‬ ‫طب‬
gluconeogenesis...‫؟‬ ‫بقي‬ ‫هيتم‬ ‫اللي‬ ‫ايه‬..
‫ال‬ ‫هرمون‬ ‫تفرزلي‬ ‫البنكرياس‬ ‫ان‬ ‫مثال‬ ‫زي‬ ‫دي‬ ‫العمليه‬ ‫هتحفز‬ ‫كتير‬ ‫حاجات‬ ‫في‬glucagon‫ال‬ ‫مثال‬ ‫زي‬ ‫تتفرز‬ ‫تانيه‬ ‫هرمونات‬ ‫او‬Epinephrine
‫وال‬Nor-epinephrine..‫ال‬ ‫االخر‬ ‫في‬ ‫وتكونلي‬ ‫بقي‬ ‫بتاعها‬ ‫بالميكانيزم‬ ‫تشتغل‬ ‫الهرمونات‬ ‫وبعدها‬Protein kinase A‫ال‬ ‫هو‬ ‫اللي‬PKA

9. 9
• During Fasting, Glucagon level increase work on liver cell receptors, then stimulate
formation of cAMP that activate formation of Protein Kinase A
‫هيعملي‬ ‫بقي‬ ‫ايه‬ ‫هيعمل‬Phosphorylation‫جزئين‬ ‫من‬ ‫بيتكون‬ ‫اللي‬ ‫االنزيم‬ ‫علي‬(PFK-2/FBPase-2)‫هيحصل‬ ‫فيهم‬ ‫واحد‬ ‫وكل‬‫حاجه‬ ‫ه‬..
‫ال‬ ‫هو‬ ‫اللي‬ ‫االوالني‬PFK-2‫هيحصله‬Inhibition‫ال‬ ‫كميه‬ ‫وبالتالي‬F-2,6-BP‫عملتلي‬ ‫قلت‬ ‫لما‬ ‫وبالتالي‬ ‫هتقل‬stimulate‫لل‬Fructose
1,6-bisphosphatase‫ال‬ ‫حدوث‬ ‫حفزت‬ ‫يعني‬gluconeogenesis‫عملت‬ ‫قلت‬ ‫لما‬ ‫كمان‬ ‫دا‬ ‫كدا‬ ‫بس‬ ‫مش‬Inhibition‫لل‬PFK-1‫عشان‬
‫ال‬ ‫يوقف‬glycolysis‫الجلوكوز‬ ‫تكسير‬ ‫ويوقف‬.
‫الثاني‬ ‫االنزيم‬ ‫اما‬FBPase-2‫بيحصله‬stimulation‫عادي‬ ‫وظيفته‬ ‫ويعمل‬ ‫عادي‬‫ال‬ ‫ويستهلك‬F-2,6-BP‫ل‬ ‫ويحوله‬fructose-6P‫فبالتالي‬
‫ال‬ ‫كميه‬F-2,6-BP‫تقل‬ ‫عماله‬.
• In Fed state increase blood glucose stimulate secretion of insulin; that
activate protein phosphatase; these enzyme activate net dephophorylation.
• When the PFK-2/FBPase-2 dual function enzyme is unphosphorylated,
then the PFK-2 activity in the enzyme is stimulated resulting in the net
phosphorylation of fructose-6P to produce more F-2,6-BP which stimulates
glycolytic flux.
‫يحصله‬ ‫ما‬ ‫قبل‬ ‫بيقولك‬ ‫هنا‬Phosphorylation‫يعني‬(dephophorylation)‫ال‬ ‫كان‬PFK-2‫ال‬ ‫بيحولي‬
fructose-6P‫ل‬F-2,6-BP..‫ال‬ ‫بيتكون‬ ‫لما‬ ‫اللي‬F-2,6-BP‫كميته‬ ‫ويزيد‬‫بيعمل‬stimulate‫لل‬PFK-1‫ال‬ ‫وبالتالي‬
glycolysis‫هتشتغل‬.
• In contrast, when PFK-2/FBPase-2 is phosphorylated, the activity of
FBPase-2 is stimulated, leading to less F-2,6-BP, and reduced flux through
glycolysis, with a concomitant increase in flux through gluconeogenesis.
‫ال‬ ‫بقي‬ ‫هنا‬PKA‫عملهم‬Phosphorylation‫فحصل‬stimulation‫لل‬FBPase-2‫ال‬ ‫فكميه‬F-2,6-BP‫قلت‬ ‫فلما‬ ‫قلت‬
‫عملت‬Stimulation‫لل‬gluconeogenesis‫و‬Inhibition‫لل‬glycolysis

10. 10
• Activation of the glucagon receptor in liver cells results in stimulation of
protein kinase A signaling, leading to an increase in gluconeogenesis,
whereas, insulin signaling stimulates protein phosphatase-1, leading to an
increase in glycolysis

11. 11
Pentose Phosphate Pathway
• We will cover three primary pathways related to carbohydrate metabolism
in non-photosynthetic organisms:
1. Pentose phosphate pathway
2. Gluconeogenesis
3. Glycogen metabolism
• Metabolism of ribose sugars in the pentose phosphate pathway is used to
generate NADPH and to provide the carbohydrate component of nucleotides.
• The major sources of carbon in gluconeogenesis are amino acids and
glycerol in animals, and glyceraldehyde-3-phosphate (GAP) in plants.

12. 12
Key Concepts: The Pentose Phosphate Pathway
• The pentose phosphate pathway takes place entirely within the
cytoplasm and is also known as the hexose monophosphate shunt or
phosphogluconate pathway.
• The most important function of the pentose phosphate pathway is to
reduce two molecules of NADP+
to NADPH (nicotinamide adenine
dinucleotide phosphate) for each glucose-6-phosphate that is
oxidatively decarboxylated to ribulose-5-phosphate.
• NADPH is functionally similar to NAD+
however, NADPH is the
primary reductant in the cell, whereas, NAD+ is the primer oxidant.
NADPH is critical to maintaining reduced glutathione levels in cells
which is required to minimized damage from reactive oxygen species.
• The pentose phosphate pathway is also responsible for producing
ribose-5-phosphate which provides the ribose sugar backbone that
anchors the nucleotide base to DNA and RNA polymers.

13. 13
♣ There are two distinct phases in the pathway.
• The first is the oxidative phase, in which NADPH is generated, and the second is the non-
oxidative synthesis of 5-carbon sugars.
• The NADPH molecules are important reductant agents that are used in fatty acid biosynthesis,
nucleotide biosynthesis, cholesterol biosynthesis, neurotransmitter biosynthesis and various
detoxification processes.
• When needed, the ribose 5-phosphate can be used to create DNA, RNA and nucleotide-bases
molecules such as ATP, NADH, FAD and CoA.
Three enzymatic reactions in the oxidative phase
• G6PD is the commitment step in the Pentose Phosphate Pathway because 6-Phosphogluconon-
d-lactone has no other metabolic fate except to be converted to 6-phosphogluconate.

14. 14
The non-oxidative phase of the Pentose Phosphate Pathway (PPP)
• The carbon shuffle reactions of the nonoxidative phase are used to regenerate glucose-6P using
the same transketolase and transaldolase enzyme reactions as the Calvin Cycle.

15. 15
• Six glucose-6P (36 carbons) are metabolized to regenerate five glucose-6P (30 carbons).
What happened to the six carbons?

16. 16
♦ Metabolic flux through the Pentose Phosphate Pathway is tightly-regulated:
• If increased NADPH is required for biosynthetic pathways.
‫ل‬‫و‬‫ع‬‫ن‬‫د‬‫ي‬‫ن‬‫ق‬‫ص‬‫ف‬‫ي‬‫ا‬‫ل‬NADPH‫ا‬‫ل‬‫ل‬‫ي‬‫ب‬‫ح‬‫ت‬‫ا‬‫ج‬‫ه‬‫ف‬‫ي‬biosynthetic pathways‫ب‬‫ض‬‫ط‬‫ر‬‫ا‬‫ع‬‫م‬‫ل‬‫ا‬‫ل‬PPP
• If cells need to replenish nucleotide pools.
‫ل‬‫و‬‫م‬‫ح‬‫ت‬‫ا‬‫ج‬‫ا‬‫ك‬‫و‬‫ن‬DNA‫ا‬‫و‬RNA‫ه‬‫ح‬‫ت‬‫ا‬‫ج‬‫ا‬‫ك‬‫و‬‫ن‬‫ا‬‫ل‬Ribose-5-p
• If ATP levels in the cell are low.
‫ل‬‫و‬‫ع‬‫ن‬‫د‬‫ي‬‫ن‬‫ق‬‫ص‬‫ف‬‫ي‬‫ا‬‫ل‬ATP‫ه‬‫ح‬‫ت‬‫ا‬‫ج‬‫ا‬‫ك‬‫و‬‫ن‬‫ا‬‫ل‬Glucose-6-p‫ع‬‫ش‬‫ا‬‫ن‬‫ت‬‫د‬‫خ‬‫ل‬‫ا‬‫ل‬glycolysis‫و‬‫ا‬‫ن‬‫ت‬‫ج‬‫ط‬‫ا‬‫ق‬‫ه‬

17. 17
◘ Regulation of the G6PD activity controls flux through the glycolytic pathway and pentose
phosphate pathways:
- When NADPH decrease, and NADP+ increase that activate G6PD (Glucose -6-phophate
dehydrogenase ) to oxidate glucose, by making Pentose phosphate pathway
- When NADPH increase and accumulate it makes feedback inhibition for G6PD so is
activate glycolysis.
Glucose-6P dehydrogenase deficiency in humans
• The pentose phosphate pathway is responsible for maintaining high levels of
NADPH in red blood cells (erythrocytes) for use as a reductant in the glutathione
reductase reaction.
• Glutathione is a tripeptide that has a free sulfhydryl group which functions as an
electron donor in a variety of coupled redox reactions in the cell.

18. 18
◘ Glucose-6P dehydrogenase deficiency in humans:
• When erythrocytes are exposed to chemicals that generate high levels of superoxide
radicals, GSH is required to reduce these damaging compounds.
• The pentose phosphate pathway in erythrocytes normally provides sufficient levels of
NADPH to maintain the GSH:GSSG ratio at about 500:1.
• Primaquine inhibits growth of the malaria parasite in red blood cells by creating a hostile
environment.
- The biochemical basis for this drug-induced illness was found to be lower than normal levels
of NADPH due to a G6PD deficiency.
• The acute hemolytic anemia seen in individuals with G6PD who are treated with primaquine
explains the symptoms of favism.
- One of the compounds in fava beans is vicine, a toxic glycoside that induces oxidative stress
in erythrocytes.

19. 19
HEXOSE MONOPHOSPHATE PATHWAY
(HMP- PATHWAY)
• The pentose phosphate pathway (also called the phosphogluconate
pathway and the hexose monophosphate shunt)
♦ Definition:
• HMP pathway is an alternative pathway for glucose oxidation involving the
formation of pentose phosphates as intermediates.
♦ Site:
• It is very active in the cytosol of certain tissues:
1. Liver
2. Lactating mammary gland
3. RBCs
4. Adipose tissue
5. Adrenal cortex
6. Eye (retina, cornea & lens)
7. Testis - Ovaries - Placenta
♦ IMPORTANCE of HMP
I. Formation of Ribose-5-P (Active ribose phosphate):
• Ribose-5-P is important for synthesis nucleotides & nucleic acids (DNA &
RNA).
• N.B. Dietary Ribose CAN NOT be utilized by our tissues and are excreted in
urine because there is NO Ribokinase enzyme to convert it to Ribose-5-
phosphate.

20. 20
II. Formation of NADPH (reduced NADP):
• NADPH is important for many enzymes and reductive synthetic pathways: e.g.
1. Synthesis of Fatty Acids (Lipogenesis).
- This occurs mainly in adipose tissue, liver and lactating mammary glands.
NADPH is coenzyme for certain reductases.
2. Synthesis of cholesterol.
- NADPH is coenzyme for b-hydroxy, b-methyl glutaryl-CoA Reductase (HMG-
CoA Reductase) the key enzyme in cholesterol biosynthesis.
3. Synthesis of steroid hormones.
- This occurs mainly in adrenal cortex, testis, ovaries and placenta.
- NADPH is coenzyme for certain hydroxylases.
4. Keeps glutathione in the reduced state (G-SH).
♣ Reduced glutathione (G-SH) functions as :
A. Coenzyme for the enzyme G-SH peroxidase which protect RBCs against H2O2.
B. Coenzyme for the enzyme met-hemoglobin reductase which keeps the iron of Hb
in the ferrous state (Fe2+
) thus preserving its capacity to carry oxygen.
C. Stabilizer to the proteins of cell membranes, particularly in RBCs.
H2O2 2 G-SH
G-S-S-G2 H2O
NADP
+
NADPH H
+
+
Glutathione
peroxidase
Glutathione
Reductase
HMP- Shunt
Se

21. 21
STEPS of HMP- PATHWAY
• Glucose-6-P is dehydrogenated to 6-phospho-gluconic acid.
- The hydrogen carrier is NADP that is reduced to NADPH.
- The reaction is catalyzed by glucose-6-phosphate dehydrogenase (G-6-PD).
• 6-phosphogluconate is dehydrogenated and decarboxylated to ribulose-5-Phosphate.
- NADP is reduced to NADPH.
- The reaction is catalyzed by 6-phospho gluconate dehydrogenase (6-P gluconate DH).
• The 2 dehydrogenases of HMP: G-6-PD and 6-P gluconate DH use NADP as hydrogen
carrier.
- NADPH
is
formed.
-‫ك‬‫م‬‫ل‬‫ب‬‫ا‬‫ق‬‫ي‬
‫ا‬‫ل‬steps
Xylulose-5-P Ribose-5-P Xylulose-5-P
Sedoheptulose-7-PGlyceraldehyde-3-P
Erythrose-4-PFructose-6-P
Glucose-6-P
Transketolase
TPP
Transaldolase
Fructose-6-P Glyceraldehyde-3-P
Transketolase
TPP
+NADPH H+
NADP+
P
C
C
C
C
C
CH2O
OH
OH
HO
H
H
H
H
O
O
PP
O
C
C
C
C
C
CH2O
OH
OH
HO
H
H
H
H
OHH
H
H
H
H
HO
OH
OH
CH2O
C
C
C
C
OH
COOH
H2O
Glucose-6-phosphate
Dehydrogenase Hydrolase
Glucose-6-phosphate 6-phospho-gluconolactone 6-phospho-gluconic acid
H
H
H
OH
OH
CH2O
C
C
C
C
OH
COOH
O
PP
NADP+
NADPH H++
6-phospho-gluconate
dehydrogenase
H
H OH
CH2O
C
C
C
OH
O
CH2OH CO2
3-keto-6-phospho-
gluconic acid
Ribulose-5-phosphate
H
CH2O
C
C
C
OH
O
CH2OH
HO H
H
H OH
CH2O
C
C
OH
C
CHO
OHH
P
P
3-epimerase
isomerase
Xylulose-5-P
Ribose-5-P
Mn++
Hexose Monophosphate Shunt ( HMP-shunt)
Isomerase

22. 22
◘ Regulation of HMP pathway:
• The key enzymes of HMP is the 2 dehydrogenases: G-6-PD and 6-P gluconate
DH.
• CHO feeding stimulates insulin secretion; insulin induces the synthesis of G-6-
PD and 6-P gluconate DH and HMP is activated.
• Fasting inhibits insulin secretion; and stimulates glucagons secretion that
represses the synthesis of G-6-PD and 6-P gluconate DH and HMP is inhibited.
• CHO feeding   blood glucose   insulin   HMP.
• Fasting   blood glucose  glucagon   HMP.
FAVISM
• Favism is an inborn error of metabolism caused by congenital deficiency of G-6-
PD enzyme due to DNA mutation of the G-6-PD gene.
• Favism is a genetically inherited disease characterized by increased fragility of
RBCs and hemolysis that occurs after intake of fava beans or after the intake of
some drugs (e.g. anti-malarial drugs).
• The congenital deficiency of G-6-PD decreases the activity of HMP pathway in
RBCs leading to decrease in reduced NADP (NADPH).
• Fava beans and certain drugs [anti-malarial drugs (primaquinone), sulfa drugs
(sulfonamides), phenacetin, nitrofurans, salicylates..] cause the increased
production of oxidizing agents and H2O2.
• No enough NADPH for reduction of oxidized glutathione (G-S-S-G) to reduced
glutathione (G-SH).
• The oxidizing agents and H2O2 attack the plasma membrane of the RBCs causing
its destruction.
• This leads to marked hemolysis and hemolytic anemia.

23. 23
• Diagnosis: Favism is diagnosed by measuring the activity of G-6-PD in RBCs.
G-6-PD activity is markedly decreased in favism.
• Treatment:
♣ No specific treatment but we can:
• Blood transfusion after the hemolytic crisis.
• Avoid the intake of fava beans and oxidizing drugs.
Main differences between glycolysis and HMP
GALACTOSE METABOLISM
• The main source of galactose in food is lactose of milk.
• Lactose by intestinal lactase gives glucose and galactose which is absorbed from
the intestine and goes via portal blood to the liver.
• In the liver: Galactose is converted to Glucose with the help of three enzymes:
galactokinase; galactose-1-P uridyl transferase or UDP-Gal 4-epimerase.

24. 24
GALACTOSEMIA
• Galactosemia is a congenital disease caused by deficiency of galactokinase;
galactose-1-P uridyl transferase or UDP-Gal 4-epimerase.
♣ Galactosemia is characterized by:
1)- Galactosemia: increased blood galactose
2)- Galactosuria: excretion of large amounts of galactose in urine.
3)- Cataract : Opacity in eye lens that looks white in color
4)- Mental retardation ( problem in the brain )
5)- Liver cell failure
• Treatment:
- It must be started early in life.
- The baby must feed lactose-free milk formula and galactose-free diet.

25. 25
FRUCTOSE METABOLISM
• Sources of fructose: Diet; Sucrose (table sugar) and fruits.
• In the liver, fructose is either converted to glucose or oxidized through the
glycolysis pathway to pyruvic acid.
• Excess fructose in liver is converted to glucose.
• The enzymes are: Fructokinase and Aldoalse-B.
• Fructose is secreted in semen in a high concentration, its level in seminal fluid is
200 – 600 mg/dl.
• Spermatozoa utilize fructose rather than glucose as a source of energy.
Inborn Errors of Fructose Metabolism
1- Essential Fructosuria:
• Inborn error of fructose metabolism caused by deficiency of Fructokinase in
liver.
- Fructose is not converted to glucose in liver, its level is increased in blood
(Fructosemia) and excreted in large amount in urine (Fructosuria).
- It is a harmless condition.
2- Hereditary Fructose Intolerance:
• Inborn error of fructose metabolism caused by congenital deficiency of Aldolase
B in liver cells.
- Ingestion of fructose or sucrose by these patients leads to fasting hypoglycemia
that might lead to coma and even death.
- Liver cell failure.
- So, Hereditary fructose intolerance is more dangerous than essential fructosuria.
• Treatment: Sucrose and fructose-free diet.
‫ا‬‫ي‬diagram‫ا‬‫و‬‫ص‬‫و‬‫ر‬‫ة‬‫م‬‫ت‬‫ح‬‫د‬‫د‬‫ه‬‫ب‬‫ا‬‫ط‬‫ا‬‫ر‬‫ا‬‫س‬‫و‬‫د‬‫غ‬‫ا‬‫م‬‫ق‬‫ي‬‫ب‬‫ق‬‫ي‬‫ع‬‫ل‬‫ي‬‫ن‬‫ا‬‫غ‬‫ي‬‫ر‬‫ك‬‫د‬‫ا‬‫ي‬‫ب‬‫ق‬‫ي‬‫ل‬‫ل‬‫ت‬‫و‬‫ض‬‫ي‬‫ح‬.