1
GLYCOLYSIS
LOCATION: CYTOPLASM
DISTRIBUTION : UBIQUITOUS
FUNCTION:
AEROBIC: TO CONVERT GLUCOSE (AND OTHER
MONOSACCHARIDES TO PYRUVATE WITH PRODUCTION OF ATP.
PYRUVATE CONVERTED TO AcCoA FOR OXIDATION BY TCA
CYCLE OR USE IN BIOSYNTHESIS (EG FA)
ANAEROBIC: ATP PRODUCTION. SOLE SOURCE OF ATP.
PYRUVATE CONVERTED TO LACTATE (OR ETHANOL OR OTHER
PRODUCTS)
CONNECTIONS:
glycogen
glucose
glu 1-P
glu 6-P
pentose phosphates
pyruvate
lactate (ethanol)
AcCoA
Fatty acids
TCA cycle
ENERGY RELATIONSHIPS:
1. from glucose
Energy requiring (preparatory) phase:
Energy yielding (pay off) phase:
glu F-1,6-bisP
F-1,6-bisP  2 pyruvate
NET:
2. from glycogen
glycogen  F-1,6-bisP
F-1,6-bisP  2 pyruvate
-1 ATP
+4 ATP
NET: +3 ATP
-2 ATP
+4 ATP
+ 2 ATP + 2NADH +H+
2
glucose
2 ADP
2 lactic acid
2 ATP
123kJ/mol
60 kJ = 49% yield
glucose
6 CO2
2828kJ/mol (Lactic yields only 2% of total
available energy)
PATHWAY
SHOW OVERHEAD OF PATHWAY
KINASES, ISOMERASES, MUTASES,
1. TRIOSE PHOSPHATE ISOMERASE: REQUIRED IN ORDER THAT ALL
OF GLUCOSE CAN BE CONVERTED TO PYRUVATE.
NOTE SOURCE OF CARBON ATOMS
NOTE: NO NET OXIDATION, INTERNAL REARRANGEMENT
2. WHY LACTIC ACID UNDER ANAEROBIC CONDITIONS?
REGENERATION OF NAD. UNDER AEROBIC CONDITIONS THIS
ACHIEVED BY MITO SHUTTLE SYSTEMS
3. PHOSPHORYLATION OF GLUCOSE
Traps glucose in cell, creates more reactive compound
Hexokinase: relatively non-specific-acts on glu, mann, fruc,
Km in low uM range, bld glu 4-8 mM therefore active most of the
time, occurs in muscle and brain. Inhibited by G-6-P
Glucokinase: (hexokinase IV, an isozyme) predominates in liver. Km 5 - 10
mM, therefore only active at high concentrations of glucose, activity
changes as [glu] changes. Not inhibited by G-6-P.
Fructokinase: (liver) fructose  F-1-P  DHAP + glyceraldehyde  G-3-P
Note: liver has high concentration of fructokinase
GLUCOSE TRANSPORTERS: Passive transport, intracellular conc lower than
serum conc. GLUT 1-7 12 TM domain proteins
Types 1 and 3 present in all cells have Km for glu of about 1 mM. Therefore
transport glucose at all times at a constant rate
3
Type 2 present primarily in liver, Km is ~60 mM (Voet and Voet), therefore
responds essentially linearly with changing bld glucose. It is never saturated and
therefore never limits the rate of glucose entry.
Type 4: muscle and fat cells: present in intracellualr vesiclaes which fuse with
membrane in of presence of insulin, thereby increasing number of
transport molecules in cell surface membrane.
4.
LACTATE DEHYDROGENASE:
EXAMPLE OF ISOZYME: heart and muscle (liver) form
Isozyme: different proteins from the same species which catalyse the
same reaction
LDH ISOZYMES
TETRAMERIC ENZYME OF VARIOUS COMBINATIONS OF A AND B
SUBUNITS
A SUBUNIT (M) HIGH IN LIVER AND MUSCLE
B SUBUNIT (H) HIGH IN HEART
A4 WORKS BEST IN DIRECTION TOWARDS LACTIC PRODUCTION AND
REGENERATION OF NAD. EG DURING ACTIVE ANAEROBIC
GLYCOLYSIS IN MUSCLE
B4 HEART USES LACTATE AS A FUEL AND CONVERTS IT TO PYRUVATE.
THIS FORM IS INHIBITED BY PYRUVATE ENSURING THAT EXCESS
PYRUVATE WILL NOT BE WASTED BY CONVERSION TO LACTATE.
5.
ENERGY CONSERVATION: substrate level phosphorylation
1. glyceraldehyde 3 P dehydrogenase
I. oxidation of CHO  COO
II. phosphorylation of COO
energy of oxidation stored in thioester and used to drive
phosphorylation reaction
see overhead
NOTE: arsenate replacec phosphate in G3P dehydogenase but then
spontaneously yields 3Pglycerate with no ATP production. AsO3-2
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WHAT IS ENERGY YIELD IN PRESENCE OF ARSNATE?
REGULATION:
allosteric
phosphorylation
1. HEXOKINASE
Inhibited by G-6-P which accumulated if other reactions are inhibited.
2. Pyruvate kinase
4 isoenzymic forms
inhibited by ATP, activated by F-1,6-Bis P see fig 12.17 Horton
liver form also inhibited by phosphorylation
3. PHOSPHOFRUCTOKINASE
Main point of regulation
 ATP, citrate
 AMP, F-2,6-bisP
inhibited by H+ ions: eg if lactic acid is not cleared pH drops and activity of
PFK1 slows
Sensitive to energy charge of the cell. NOTE: [ATP} remains relatively
constant but large changes in AMP and AP occur because they are present in lower
concentration. Thus a small decrease in [ATP] results in large change in AMP
ATP  ADP
2 ADP ATP + AMP
FRUCTOSE-2,6-BISP
Discovered in 1980
Potent activator of PFK, effective in uM range
F-6-P  F-2,6-bisP PFK-2/fructose-2,6-bisphosphatase (single enzyme in liver)
PFK-2 is inhibited by citrate and by phosphorylation whereas F26bPase is
stimulated by phosphorylation
SUMMARY
ALLOSTERIC REGULATION
hexokinase
 G6P
PFK
 ATP, citrate
 AMP, F26bisP
PFK-2
F26bisPase
 citrate, phosphorylation
 phosphorylation
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pyruvate kinase
 F-16-bisP
 phosphorylation
PHOSPHORYLATION
pyr kinase
PFK-2
decreases
F2,6 bis Pase (liver) result [F2,6,bisP] drops and activity of PFK1
Phosphorylation results in  PK activity, a drop in F-2,6 bisPase, and a  PFKase
Therefore phosphorylation results in inhibition of glycolysis in liver
Phosphorylation increases when bld glucose levels are low in response to the
presence of the hormone glucagon in the blood.
PASTEUR EFFECT
Inhibition of glucose consumption by oxygen