Glycolysis II

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Glycolysis II
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Glucose Transport
Glucose Transport by Facilitated Diffusion
Outside
Cell Membrane
Inside
Facilitated Diffusion Concentration gradient No
chemical changes
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Insulin-Dependent TransporterGLUT 4
-GLUT4 is found in skeletal muscle and fat cells-
Glc
Glc
Intracellular Signals
No insulin, no transport GLUT4 visicles
translocated to membrane Defective
translocation-Type 2 Diabetes
GLUT4 vesicles
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Insulin Independent Transporters
-Found in almost all cells-
Glc
Glc
Glc
Glc
Glc
Glc
Glc
Intracellular Signals
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The Glucose Transporter Family

• GLUT1 most cells, continual glucose uptake. Km
  1 mM
• GLUT2 Liver and Pancreatic b-cells, transports
  at high Glc
• concentrations only. Insulin secretion
  role in b -cells.
• Km gt15 mM
• GLUT3 Functions like GLUT 1
• GLUT4 Muscle and Fat Cells, insulin dependent.
  Increases
• with physical training. Km 5 mM.
• GLUT5 Small Intestine, transports mainly
  fructose.
• (Blood Glc concentration 4-8 mM)

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Phosphofructokinase 1 (all cells)
Irreversible
Fructose 6-P
ATP.Mg
Phosphofructokinase 1 PFK-1
ADP.Mg
F-1,6-BP
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Phosphofructokinase 1 (liver kidney)
Irreversible
Liver Kidney
Irreversible
F-6-P
ATP.Mg
Pi
Phosphofructokinase 1 PFK-1
F-1,6-Bisphosphatase FBPase-1
ADP.Mg
H2O
F-1,6-BP
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Regulation of PFK-1 by Energy Charge
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Regulation of PFK1 by F-2,6-BP
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Dihydroxyacetone Phosphate (DHAP) is a precursor
to Glycerol 3-Phosphate
If lipids are being synthesized, this is a way of
providing the glycerol backbone and oxidizing
excess NADH.
If glycerolipids , e.g., fats, are being
hydrolyzed, the free glycerol may
be phosphorylated to glycerol 3-P, which may be
oxidized to DHAP and utilized in the glycolytic
pathway.
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Anhydrides and Esters
Anhydride acid acid (phosphate-phosphate or
carboxyl-phosphate Ester acid alcohol
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Regulation of Glucokinase in Liver
Glc
Glucokinase
ATP
Reaction occurs only when glucose levels are
high. This is because of the high Km of
glucokinase for Glc.
ADP
Glc-6-P
Glucose 6-P is now high and proceeds
to synthesize fructose 6-P so that it is now high.
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Regulation of PFK-1 FBPase-1 in Liver (by
F-2,6-BP)
F-6-P
FBPase2
F-6-P
F-2,6-BP
F-6-P
PFK2
FBPase1
F-6-P
PFK1
F-2,6-BP
F-2,6-BP
High F-6-P stimulates glycolysis via F-2,6-BP
Low F-6-P stimulates gluconeogenesis via lack
of F-2,6-BP
F-1,6-BP
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Regulation of Glycolysis by Covalent Modification
F-6-P
FBPase2
F-6-P
F-2,6-BP
F-6-P
PFK2
FBPase1
F-6-P
PFK1
F-2,6-BP
F-2,6-BP
F-1,6-BP
Glucagon
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Feed-forward regulation by fructose
1,6-bisphosphate
F-1,6-BP
PEP
Pyruvate Kinase
Feed Forward Regulation
Pyruvate
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Regulation of PFK-1 FBPase-1 in Liverby ATP,
AMP, Citrate F-2,6-BP
F-6-P
FBPase2
F-6-P
F-2,6-BP
PFK2
FBPase1
F-6-P
PFK1
AMP
F-2,6-BP
F-2,6-BP
AMP
ATP Citrate
ATP Citrate
Normal glucose
High energy charge
F-1,6-BP
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ATP Yield of Glycolysis
Anaerobic 2P net per Glc
Aerobic about 4-6P net per Glc
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Applications of Glycolysis

• Fat from carbohydrate
• Cori cycle
• Aerobic fate of lactate
• Ethanol metabolism and health
• Poisonings from other alcohols
• Oxalic acid in medicine
• Lacticacidosis
• Hypophosphatemia

• NAD/NADH ratio
• Oxygen and the brain
• Glucose and the brain
• 2,3-BPG
• Defective pyruvate kinase in RBC
• Positron Emission Tomography
• Fates of pyruvate

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Fat from Carbohydrate (Liver)
Excess Carbohydrate
Glycolysis
Fat (Triacylglycerols)
G-3-P Dehydrog
G-3-P
Pyr
TCA, etc.
FAS, etc.
AcCoA
AcCoA
Fatty Acids
Mitochondrion
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Lactate-The Cori Cycle
Liver
Blood
Skeletal Muscle
Lactate
Gluconeogenesis
Glycolysis
Glucose
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Aerobic Fate of Lactate
Aerobic
Lactate
CO2

H2O
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Alcoholic Fermentation
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Metabolism of Ethanol
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Ethanol

• Ethanol is rapidly oxidized to acetyl CoA.
• Ethanol is an energy source
• Distilled spirits - empty calories
• Precursor to fatty acid, cholesterol, ketones
• Hypoglycemia - Impairs gluconeogenesis because of
  high NADH/NAD ratio.
• Fatty liver, cirrhosis of liver, esophageal
  varices, dementia
• LD50 7g/kg 560ml for a person

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Alcohol poisoning from other alcohols

• Alcohol dehydrogenase and aldehyde dehydrogenase
  lack specificity.

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Alcohol ProblemsShow how each is metabolized.
1 alcohol dehydrogenase 2 acetaldehyde
dehydrogenase
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Drugs for treatment of alcohol poisonings
4-MP, Fomepizole, or Antizol is an inhibitor of
alcohol dehydrogenase.
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Nutrition and Oxalic Acid
Some foods are high in oxalic acid. This is
important for several reasons.
1. People prone to kidney stones composed of
oxalate.
2. People seeking non-dairy sources of calcium
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Oxalate in Foods
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Oxalic Acid in Medicine

• Some people are susceptible to kidney stones
• made of oxalate.
• - They need to avoid foods high in oxalate.
• -Calcium oxalate can precipitate in kidneys.
• Oxalate forms calcium oxalate, making calcium
  unavailable from some foods.
• 60 not absorbed
• Green leafy vegetables have high calcium, but
  also oxalate.
• Higher amounts of these vegetables are
  recommended for adequate calcium intake.
• Other phosphates, such as phytic acid also
  complex calcium.

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Lacticacidosis

• Excessive lactic acid will cause the pH of blood
  and other fluids to be acidic.
• This happens when buffers can no longer
  compensate for excessive acidity.
• Lacticacidosis can occur when
• Anaerobic conditions exist.
• Glucose 6-phosphate cannot be hydrolyzed to free
  glucose in liver and kidney.
• Chronic alcoholism exists. (NADH/NAD ratio)
• Any defect from pyruvate to mitochondrial ATP
  synthesis (Leighs disease)

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Hypophosphatemia

• Low phosphate levels in blood
• Occurs in conditions such as fructose intolerance
  (one of your readings)
• Glyceraldehyde 3-P dehydrogenase requires Pi and
  could be impaired
• Pi is also required for glycogenolysis, which can
  lead to hypoglycemia

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NADH/NAD Ratio

• The NADH/NAD ratio in the cytosol is normally
  low.
• If it increases, the ratio of lactate/pyruvate
  increases.
• If too high in liver, gluconeogenesis will be
  impaired, leading to hypoglycemia.
• It is common in chronic alcoholism.

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Oxygen the Brain

• During birth, O2 is conserved for the brain by
  restricting blood flow to other tissues. This
  way, the brain remains aerobic and can make ATP
  via glycolysis and aerobic metabolism.
• Other tissues will relie on glycolysis for ATP.
• Diving mammals have a similar physiological
  response during a dive. Many have huge stores of
  myoglobin in skeletal muscles to store O2 for use
  during a dive.

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Glucose the Brain

• Brain has absolute requirement for glucose.
• Uses about 120g/day.
• Liver stores only about 200g.
• Potatoes 78 water, 2 protein, 1 lipid, 18
  carbohydrate
• Amino acids are the most important source of
  glucose, not fats.
• Brain uses less glucose during ketosis, because
  the ketones spare glucose.

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Irreversible Steps in Glycolysis
Glucose
ATP
Hexokinase, Glucokinase
ADP
Glucose 6-P
Fructose 6-P
ATP
Phosphofructokinase 1
ADP
Fructose 1,6-BP
2PEP
2ADP
Pyruvate Kinase
2ATP
2Pyr
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2,3-Bisphosphoglycerate
Especially Important in RBC
1,3-BPG Mutase
1,3-BPG
Phosphoglycerate Kinase
2,3-BPG
Pi
2,3-BPG Phosphatase
3-BPG
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Functions of 2,3-BPG

• Required by phosphoglycerate mutase
• Regulates oxygen affinity of hemoglobin
• 2,3-BPG decreases O2 affinity.

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RBC Defect

• Defective pyruvate kinase increases the
  concentration of 2,3-BPG
• Oxygen affinity by Hb is decreased
• Delivery of oxygen impaired, because it will not
  bind enough oxygen to meet metabolic demands

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Positron Emission Tomography
Metabolically active cells take up glucose more
rapidly. Cancer cells are known to have more
rapid glycolysis. A radioactive analog of glucose
may be used to detect metabolically active
cells, such as cancerous cells. Fluorodeoxyglucose
(FDG) is often used.
FDG is taken up through a GLUT and is converted
to FDG-6-P by hexokinase, but is not further
metabolized. The positrons it emits are detected
and a computerized image generated.
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Positron Emission Tomography (PET)
In PET, a radioactive substance, such as
fluorodeoxyglucose is injected, and its positrons
are detected. Metabolically active tissues and
tumors take up glucose at more rapid rates than
other cells, so they can be detected. In
addition, dead tissues can also be detected by
comparing images to what is expected normally. In
the image above, a lymphoma in the axilla is
detected by PET, which would have probably been
overlooked using CT. (image used with permission)
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Fates of Pyruvate
Pyruvate
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Dont forget these

• Glucose to glycerol 3-P
• Glycerol to glucose
• Glucose to glycogen
• Glucose to 2,3-BPG
• LDH and its isozymes
• Fates of pyruvate

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Regulation of glycolysis

• Allosteric regulation by ATP, citrate, AMP and
  fructose 2,6-bisphosphate
• Covalent modification by protein kinase A (PKA)
  and protein phosphatase. (phosphorylation and
  dephosphorylation)
• Enzyme protein biosynthesis and degradation.

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Key liver enzymes are regulated at the genetic
level (induction/repression)

• Induced with high insulin
• Glucokinase
• Phosphofructokinase1
• Glycogen synthase
• Repressed with high insulin
• Glucose 6-phosphatase
• Fructose 1,6-bisphosphatase
• Pyruvate kinase
• Glycogen phosphorylase

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Induction/repression of liver glycolytic enzymes
continued

• Enzymes induced with low insulin
• Glucose 6-phosphatase
• Fructose 1,6-bisphosphatase
• Glycogen phosphorylase
• Enzymes repressed with low insulin
• Glucokinase
• Phosphofructokinase1
• Pyruvate kinase
• Glycogen synthase