Topic 6: Regulation of Glycolysis

Question 1

How is glycolysis primarily regulated?

Answer 1

Insulin and Glucagon with some contribution by ATP and other metabolites.

Question 2

What does insulin want the body to do?

Answer 2

Get glucose out of the bloodstream. Take it up and burn it (glycolysis +++) or store it (glycogenesis +++).

Question 3

What Steps/Enzymes are UP-regulated by insulin?

Answer 3

Step 1/Glucokinase in the liver
Step 3/PFK
Step 9/Pyruvate Kinase

Question 4

How does ATP/ADP/AMP affect regulation of glycolysis?

Answer 4

As ATP is burned [ADP] increases to a point where AMP Kinase will be activated. AMP Kinase turns 2 ADP into 1ATP and 1AMP for some energy

When AMP is high the body knows we need energy and ramps up PFK/Step 3.

The opposite of that, if ATP is high we don’t need energy and ATP inhibits PFK.

Question 5

What is the significance of Fructose-2,6-bisphosphate?

Answer 5

F-2,6-BP further stimulates PFK-1/Step 3 to get its shit in gear. It is made from PFK-2 which has a higher Km for F-6-P than PFK-1.

This is a regulator step, not associated with energy production.

Question 6

How is Pyruvate Kinase turned off?

Answer 6

Protein Kinase A phosphorylates it, turning it OFF.

Elevated levels of Alanine. Which is another source of pyruvate, so if it’s high we don’t need pyruvate and it tells pyruvate kinase to slow its roll.

Question 7

How is Pyruvate Kinase turned on?

Answer 7

Protein Phosphorylase removes the phosphate, turning it ON.

Question 8

What substrate other than insulin activates pyruvate kinase?

Answer 8

Fructose-1,6-Phosphate by feed forward activation.

Question 9

What would you expect the phosphorylation state of pyruvate kinase in the FED state to be?

Answer 9

NOT phosphorylated. Need it to be active. Insulin:Glucagon ratio will be UP, activating Protein Phosphorylase to turn on pyruvate kinase.

Question 10

What would you expect the phosphorylation state of pyruvate kinase in the FASTED state to be?

Answer 10

Phosphorylated! Need to be deactivated. Insulin:Glucagon ratio will be DOWN, activating Protein Kinase A to phosphorylate pyruvate kinase and turn it off.

Question 11

How does the insulin:glucagon ratio affect Pyruvate Kinase?

Answer 11

When it’s UP - activates Protein Phosphorylase for activation of enzyme.

When it’s DOWN - activates Protein Kinase A for INactivation of enzyme.

Question 12

What does lactate dehydrogenase (LDH) do?

Answer 12

Using NADH Reduces Pyruvate (impermeable) to Lactate (permeable) allowing regeneration of NAD+ so we can continue glycolysis. Lactate can then be dumped to the blood for utilzation (mainly in the liver) as an energy source.

LDH can also do the reverse of this.

Question 13

Is oxygen necessary for glycolysis?

Answer 13

NO - anaerobic process. Only method of ATP generation for RBCs and they have no mitochondria.

Question 14

What tissues are absolutely reliant upon glycolysis for energy?

Answer 14

RBCs, white muscle fibers, cornea, lens, retina

Most cancer cells also.

Question 15

If NAD+/NADH are impermeable to mitochondrial membranes how does cytoplasmic NADH (from Step 5 in glycolysis) get into the matrix?

Answer 15

They shuttle their H+ and e- via Glycerol phosphate shuttle and/or the Malate-Aspartate Shuttle.

Question 16

Which shuttle pathway is faster?

Answer 16

Glycerol Phosphate Shuttle but less ATP

Question 17

How much ATP does each shuttle pathway make?

Answer 17

Malate-Aspartate Shuttle 2.5 ATP

Glycerol Phosphate Shuttle 1.5 ATP

Question 18

How does the Glycerol Phosphate Shuttle work?

Answer 18

DHAP from Step 4 of glycolysis via Glycerol 3-P Dehydrogenase picks up the H+ and e- from NADH to make Glycerol-3-Phosphate which crosses the OMM.

Using the same enzyme (G-3-PDH) G-3-P hands off the H+ and e- to FAD to make FADH2 which proceeds to Complex 2 of ETC.

Question 19

What tissues do we see the Glycerol Phosphate Shuttle in?

Answer 19

brown fat, brain, skeletal muscle, ß-cells

is an irreverisble reaction

Question 20

How does the Malate-Aspartate Shuttle work?

Answer 20

Malate Dehydrogenase takes H+ and e- from NADH and puts on OAA to make Malate. Malate crosses IMM and in the matrix Malate DH reverses the reaction, regenerating NADH which proceeds to the ETC at Complex 1.

Malate crosses the IMM via Malate/A-KG antiport. A-KG must be generated via AA transferase from Glu. During this rxn OAA becomes Aspartate which drives the Asp/Glu antiport. This rxn takes place on both sides of the membrane and fuels the shuttle, supplying OAA to become malate and vice versa.

It’s a vicious cycle.

Question 21

What tissues do we see the Malate-Aspartate Shuttle in ?

Answer 21

liver, heart, kidney

is a reversible reaction

Question 22

What is the net yield ATP of oxidation of glucose?

Answer 22

It depends on which shuttle you use but between 30-32 ATP

Question 23

What would you expect to see form a Pyruvate Kinase (Step 9 glycolysis) deficiency?

Answer 23

Hemolytic Anemia: RBCs can’t make pyruvate for energy and membranes fall apart. They lack ATP, cannot fuel Na+/K+ Pump –> osmotic imbalance –> rupture

Question 24

What breeds are predisosped to Pyruvate Kinase Deficiency?

Answer 24

Beagles, Basenjis, Cairn Terriers, West Highland Terriers, Amer Eskimo Dogs, Abyssinian cats

Question 25

What would you expect to see in a PFK (Step 3 of glycolysis) deficiency?

Answer 25

Muscle and RBCs affected

Question 26

What breeds are predisposed to PFK deficiency?

Answer 26

English Springer Spaniels and American Cocker Spaniels

Question 27

How do sorbitol cataracts form?

Answer 27

Glucose via Aldose Reductase (AR) becomes sorbitol which becomes Fructose via Sorbitol-DH

Excess glucose pushes Sorbitol formation which is poorly permeable and will accumulate in the cell, osmotically drawing in water and can destroy the lens cells –> and BOOM you get CATARACTS.

This is why diabetics have cataract formation.

Question 28

What is malignant hyperthermia and pickled pigs?

Answer 28

Genetically inherited defect in the Ryanodine receptor of muscle (Ca++ release in the sarcoplasmic reticulum). This causes uncontrolled stimulation of heat and lactic acid buildup. The HEAT is what kills.

Caused by Anesthetics (halothane gas) and Succinylcholine gas

Question 29

What animals do you see malignant hyperthermia and pickled pigs?

Answer 29

Seen in pigs as Porcine Stress Syndrome (shipping and halothane gas)

Quarter Horses and Dogs