GLYCOLYSIS
Dr Vivek Joshi,MD
Fall 2015
Learning Objectives
Introduction
Bio
Medical Importance
Site
Reactions
of the pathway
Energetic of Glycolysis
Regulation of the pathway
Clinical Significance
Introduction
Glycolysis was one of the first metabolic pathways
studied and is also one of the best understood
Also known as the Embden-Meyerhof pathway
Introduction

Major pathway for oxidation of Glucose
Glucose
Pyruvate/Lactate
Glycolysis: Aerobic /Anaerobic

Aerobic –Glucose


Pyruvate
NADH + H+
NAD+
ETC-ATP

Anaerobic
Glucose
NADH + H+
Pyruvate
NAD+
Lactate
Bio Medical Importance




Provision of energy
Anaerobic Glycolysis-Skeletal muscle during
exercise
Aerobic Glycolysis- Heart muscles -Poor
survival under ischemic conditions
Hemolytic anemia- Pyruvate kinase deficiency
Sites of Glycolysis


Sub cellular site :
 In the cytoplasm of eukaryotic Cells
Tissue site :
 Occurs in practically all living cells
 Aerobic glycolysis
 In the presence of oxygen
 In the Cells with mitochondria
 Anaerobic glycolysis
 In the absence of oxygen
 In the RBCs & contracting skeletal muscle
Reactions of the pathway
1stIrreversible Step
Glucose to Glucose 6-phosphate by Hexokinase/Glucokinase
-Nonionic glucose is converted into an anion that is
trapped in the cell, since cells lack transport systems for
phosphorylated sugar.
-Biologically inert glucose becomes activated into a labile
form capable of being further metabolized
Hexokinase v/s Glucokinase

Uptake of Glucose and phosphorylation
 Uptake of Glucose by the tissue-Glucose
transporters(GLUT)
 Phosphorylation of Glucose
 Hexokinase
Wide tissue distribution
Low Km (High affinity for glucose)
Low Vmax
Inhibited by Glucose-6-P
Utilization of glucose to provide energy even
when [glucose] is low
Glucokinase
Liver & islet cells of pancreas
High Km- Low affinity for the substrate
High Vmax -Can effectively phosphorylate Glucose in the cell.
Induced by Insulin
At high blood glucose levels (After meals)-Glucose uptake by
GLUT 2 in the liver and pancreas with phosphorylation by
Glucokinase
Acts as ‘glucose sensor’ in islets cells of pancreas–determines
threshold for insulin secretion
Hexokinase v/s Glucokinase
Conversion of Glucose 6-phosphate to Fructose
6-phosphate
2nd Irreversible step- Fructose 6 phosphate to
Fructose 1,6 bisphosphate by Phosphofructokinase -1
PFK-1 is the most regulated enzyme.
Cleavage of (6C) Fructose 1,6 biphosphate to 2
triose sugars
Phosphotriose Isomerase converts dihydroxyacetone
phosphate to Glyceraldehyde 3-phosphate
Glyceraldehyde 3-phosphate Dehydrogenase
catalyzes the only step where NADH is synthesized
Phosphoglycerate kinase catalyzes the first
substrate-level phosphorylation step in glycolysis
A mutase moves the phosphate from a 3- to
a 2- position on glycerate
Enolase results in generation of the high-energy
bond in Phosphoenolpyruvate
Enolase is inhibited by Fluoride (used in blood
collection tubes for blood glucose estimations)
Pyruvate kinase catalyzes the second substratelevel phosphorylation step in glycolysis
Metabolic Fate of Pyruvate
Glucose
Alanine
Aerobic Glycolysis
LDH
Transaminase
Lactate
PYRUVATE
CO2
CoASH
Pyruvate
Dehydrogenase
Pyruvate Carboxylase
(BIOTIN)
CO 2
NAD +
NADH + H+
ACETYL Co A
CITRIC ACID CYCLE (TCA)
ATP
ADP
OXALOACETATE
GLUCONEOGENESIS
Metabolic Fate of Pyruvate

Aerobic conditions (Presence of oxygen)
Pyruvate can be converted to acetyl-CoA and enter the
Krebs Cycle
 Acetyl-CoA is completely oxidized during Krebs cycle
and generates ATP through oxidative phosphorylation


Anerobic conditions (Absence of oxygen)/Absence
of mitochondria
Seen mainly in RBCs and the contracting skeletal
muscle
 Pyruvate is converted to lactate

Conversion of Pyruvate to Lactate by Lactate
Dehydrogenase (LDH)
NADH + H+
NAD+
Pyruvate
Lactate
Lactate Dehydrogenase (LDH)
Lactate is the final product of anerobic glycolysis
Is formed mainly in the RBC, lens and cornea of the
eye, kidney medulla, testes and leukocytes
Is also formed in the intensely exercising skeletal
muscle ( accumulation causes cramps)
Energy yield of Glycolysis
Aerobic Glycolysis
(Glucose to pyruvate) =
8 ATP/mol of glucose
Glucose + 2 Pi + 2 ADP + 2 NAD
Anaerobic Glycolysis
(Glucose to lactate) =
2 ATP/mol of glucose
Glucose + 2 Pi + 2 ADP
2 Pyruvate + 2 ATP + 2 NADH
2 Lactate + 2 ATP
Regulation of Glycolysis

Irreversible and Regulated steps catalyzed by:
 Glucokinase- Induction and Repression
 Hexokinase- Product Inhibition
 Phosphofructokinase-1- Allosteric Regulation
( Most regulated enzyme)
 Pyruvate Kinase- Covalent Modification
PFK-2 (Controls PFK-1 of Glycolysis in the liver)-Covalent Modification
HEXOKINASE
Product Inhibition –Inhibited by Glucose -6-P(Product)
GLUCOKINASE
 Induced
by Insulin
 Near complete Deficiency-Neonatal Type I
Diabetes
 Mutation of Glucokinase gene
Decrease Km- Hyperinsulinemia and
Hypoglycemia
Increase Km-Maturity Onset Diabetes of
the Young(MODY)
Phosphofructokinase-1(PFK-1)
 Most
Regulated Enzyme
 Positive Allosteric Effector- High
Fructose -2,6 bis phosphate (Liver) High
ADP (Liver)/ High AMP(Muscle)
 Negative Allosteric Effector –Citrate
(Liver)
Phosphofructokinase-1(PFK-1)
Potent activator -Fructose 2,6 bisphosphate (F2,6BP)
F2,6 BP
Fructose 2,6 bisphosphate (F2,6BP)
Fructose-6
Fructose-1,6 BP
PFK-1
+
Fructose-6
Fructose-2,6 BP
PFK-2
Phosphofructokinase-2(PFK-2)
Synthesis of F2,6BP is catalyzed by the bifunctional enzyme
Phosphofructokinase-2/fructose-2,6-bisphosphatase
(PFK-2/F-2,6-BPase)
Phosphofructokinase1(PFK-1)InhibitorsCitrate and ATP
The only example
of a citric acid cycle
intermediate
regulating a
glycolytic enzyme
Pyruvate Kinase
Pyruvate Kinase
Glucagon
- Pyruvate Kinase-P
(Inactive)
-PFK-2-P (Inactive)
Pyruvate Kinase
Glucagon/Epinephrine
-Pyruvate Kinase-P
(Inactive)
-PFK-2-P (Inactive)
Pyruvate Kinase
Pyruvate Kinase
(Active)
(Inactive)
GLYCOLYSIS IS
INHIBITED
High Glucagon (cAMP) as in hypoglycemia
F 6BP
Active Protein kinase A
P
PFK-2
Active
F 2,6BP
F26BPase
inactive
ATP
ADP
PFK-2
Inactive
Decreased
GLYCOLYSIS
F26BPase
active
P
High Glucagon (cAMP) –PFK-2 Inactive………

Fructose-2,6-bisphosphate thus decreases in liver
cells in response to a glucagon-activated cAMP
signal cascade. Downstream effects include:

Glycolysis slows because of the decreased
concentration of fructose-2,6-bisphosphate

Gluconeogenesis Increases because of the
decreased concentration of fructose-2,6bisphosphate
Hormonal Control over Glycolysis


Well fed state/Carbohydrate rich diet /High Insulin- INCREASE in the :
 Uptake of Glucose by GLUT 4 (Skeletal muscle and adipose tissue)
 Utilization of glucose by oxidation
 Anabolic pathways
Hypoglycemia/Fasting /Starvation/ High Glucagon/EpinephrineDECREASE in the :
 Utilization of glucose by oxidation by Inactivation/Repression of the
key Glycolytic enzymes
Clinical Significance
Enzyme deficiencies -Pyruvate kinase Deficiency
Lactic Acidosis
Cancer cells
2,3,Bisphosphoglycerate
Fluoride and blood glucose estimations
Pyruvate kinase deficiency




Genetic defect associated with mutant enzyme-A severe
decrease in Pyruvate kinase activity and rate of glycolysis
Affects mainly RBCs that depend solely on anaerobic
glycolysis for energy and maintaining structural integrity
Associated with the rise in 2,3-BPG levels-Shift of ODC to
the right
Clinical presentation:
# Hemolytic Anemia due to lysis of RBCs; usually
associated with precipitating factors (oxidant stress,
infection)
#Diagnosis: Levels of pyruvate kinase activity in RBCs
#Treatment: Usually no therapy required
Lactic Acidosis



Accumulation of lactic acid in blood
As a result of failure of delivery of oxygen to tissues –
Dependent on anerobic glycolysis
May be seen associated with:
 Severe myocardial infarction
 Cardiac muscles-Adapted for aerobic Glycolysis
 Poor survival under ischemic conditions
 Uncontrolled hemorrhage
Cancer cells
 Very rapid glucose uptake
(shown in 1928 by the German
Biochemist, Otto Warburg)
 Commonly experience hypoxia
and depend on anaerobic
glycolysis for most of their ATP
 Have a very HIGH glycolytic
rate (lesser mitochondria)
The 2,3-Bisphosphoglycerate Pathway in
Erythrocytes

Mature Erythrocytes Dependent on Glucose as fuel
Glucose oxidized by Anaerobic Glycolysis(Lack
Mitochondria) for Energy ,maintain ion channel and
structural integrity
Enzyme Bisphosphoglycerate mutase Synthesize 2,3Bisphosphoglycerate is synthesized from an
intermediate of glycolysis, 1,3 Bisphosphoglycerate
The 2,3-Bisphosphoglycerate Pathway in
Erythrocytes
RECALL…………………..

2,3-BPG in the RBC’s
 Stabilises the Taut form/ “T” /deoxy form of Hb
 Favours unloading of Oxygen to the tissues
 High BPG content shifts Oxygen dissociation curve to
the right
 High Altitude –Increased 2,3-BPG
 Fetus-Inability of 2,3-BPG to bind to fetal Hb ( chains)
Fluoride and Blood Glucose estimations

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Blood glucose concentration is used for the diagnosis
of Diabetes
Fluoride bulb is used for blood glucose estimation Mixture of anticoagulant with Sodium Fluoride
(Enzyme inhibitor)
Fluoride (used as sodium fluoride) is a strong
competitive inhibitor of Enolase, blocking glycolysis.
Addition of Enzyme inhibitor to the blood inhibits
Glucose utilisation in vitro .
Prevents false low values for blood glucose

Thank You