Regulation of glycolysis and gluconeogenesis Flashcards
The Pasteur Effect
Anaerobic yeast are exposed to oxygen and their rate of glucose utilization decreases greatly and they become more efficient because aerobic glycolysis produces 30-32 ATP per 1 glucose whereas anaerobic glycolysis produces 2 ATP and 2NADH per 1 glucose
What is the important control point of anaerobic glycolysis
Intracellular levels of glycolytic intermediates after oxygenation are pointing towards the conversion of F6P to F1,6BP as an important control point (PFK). (add oxygen at reaction 3 = less glucose is used)
Glycolysis and gluconeogenesis are controlled where?
1) Reaciton 1
2) Reaction 3
3) Reaction 10
Regulation of glycolysis and gluconeogenesis is mostly achieved by
allosteric regulators
Allosteric Control (Allostery)
Modulator binds to regulatory site to either make enzyme more or less efficient (can be positive or negative effects)
In image:
Green Line = more efficient
Red line = less efficient
Overall regulation map of glycolysis and gluconeogenesis
Reaction 1 at top of image
Reaction 3 in the middle
Reaction 10 at bottom
Regulation of glycolysis reaction 1 is controlled by (2 things)
1) Allosteric control of hexokinase
2) Inhibited by glucose-6-phosphatase
Is reaction 1 regulation true for all organs
No, muscle and liver will have different regulation
Characteristics of Reaction 1 regulation by Hexokinase I (possibly 1-3?)
1) Hexokinase I (muscles and most others tissues)
2) Inhibited by glucose-6-phosphate
Characteristics of Reaction 1 regulation by Hexokinase IV
1) Not inhibited by glucose-6-phosphate
2) Because glucokinase is NOT inhibited by G6P, it can keep producing G6P at [ ] at which hexokinase I would have long been inhibited. This G6P can be used in other pathways, such as glycogen metabolism and pentose phosphate pathway.
Compare and contrast the vmax of hexokinase I vs hexokinase IV
1) Hexokinase I is always at Vmax so will produce maximum, but there is feedback to stop its use
2) Hexokinase IV is regulated on blood glucose concentrations and does not reach vmax easily
Explain the regulation system of hexokinase IV
- GLUT2, establishes an equilibrium between the concentration of glucose in the blood and the hepatocytes (liver cells).
2.When the concentration of glucose increases, the increasing concentration in glucose will act as an allosteric inhibitor of the glucokinase (hexokinase IV) regulatory protein(GKRP).
- GKRP sequesters hexokinase IV in the nucleus
- Under high glucose conditions, hexokinase IV is released to the cytosol.
low glucose = hexokinase IV in the liver will not work
high glucose = hexokinase IV in the liver will work
Explain this image
1) When high levels of blood glucose, it moves into the cytosol and is converted by hexokinase IV (which moves into the cytosol) to G6P
- When low levels of blood glucose, means less glucose in the cytosol, fructose 6-phosphate acts as an allosteric activator of GKRP, increasing its binding to hexokinase IV so the hexokinase IV stays bound to the regulatory protein in the nucleus
**High glucose sequesters hexokinase IV into the cytosol
**Low glucose = GKRP sequesters hexokinase IV in the nucleus
Regulation of Reaction 11 (reaction 1 glycolysis) of gluconeogenesis
Conversion of glucose-6-phosphate into glucose by the glucose-6-phosphatase will be promoted at high [ ] of G6P.
Explain the regulation in terms of Vmax for reaction 11 of gluconeogenesis
1) The glucose-6-phosphatase KM (2-3 mM) is higher than the intracellular concentration of G6P (0.05-0.1 mM).
2) Therefore, the activity of the enzyme will increase in relation to the increase in G6P concentration and G6P increased concentration will push the enzyme to Vmax and increase the activity
Regulation of glycolysis reaction 3
Phosphofructokinase is inhibited by energy level sensor:
1) ATP is a substrate and an inhibitor. It binds to the active site as well an allosteric site on PFK
2) In the presence of an excess of ATP, Acetyl CoA, and citrate, ATP bind to an allosteric site and PFK activity is inhibited.
3) When the energy charge (level of ATP) is low, PFK will be activated by the binding ADP to the allosteric site.
** Citrate is also a good indicator of the level of energy charge in the cell. An elevated [ ] of citrate, which is an intermediate of the TCA cycle, is an indication of a high energy charge and therefore, it will inhibit PFK’s activity
T or F: What happens with regulation on one side for glycolysis = does the opposite for gluconeogenesis
True
Explain high ATP vs low ATP for regulation of reaction 3
Low ATP = reach Vmax earlier and glycolysis is increased
High ATP = take longer to reach Vmax because glycolysisis is slowed down
Allosteric control of PFK-1 (reaction 3 glycolysis)
High AMP/ADP and low ATP (reaction 3 glycolysis
Increases activity of PFK-1 because AMP,ADP changes conformation for substrate binding site for F6P to bind to and form FBP (Allows ATP and F6P to bind)
High ATP and low AMP/ADP (reaction 3 glycolysis)
Decreases activity of PFK-1 because ATP binds to regulatory site and the catalytic pocket does not change shape to allow substrate binding
PFK (regulation of glycolysis reaction 3) is also positively regulated by
fructose 2,6-bisphosphate (F2,6 BP) which is generated by PFK/FBPase-2 enzyme
T or F: Bifunctional PFK-2/FBPase-2 (regulator) is not distinct from the enzymes found in glycolysis and gluconeogenesis
False, it is distinct as Both activities are found in the same enzyme, the difference is that there is a phosphate on Carbon 2 now
Explain the graph representation of how PFK is positive regulated by fructose-2, 6-bisphosphate (F26BP)
Vmax is reached much sooner when F26BP is present than when it is not present
Explain the substrate regulation of PFK when there is high F2,6BP
Explain the substrate regulation of PFK when there is low F2,6BP
Regulation of gluconeogenesis reaction 9
fructose-1,6-biphosphatase is negatively regulated by fructose-2, 6-bisphosphate (F2,6BP).
fructose-2, 6-bisphosphate (F2,6BP) is a
master regulator because on one end it will have a positive effect on PFK-1 and then a negative effect on the other side of FBPase-1
fructose-2, 6-bisphosphate (F2,6BP) is important in
the liver because it is regulated by hormones
Reaction 3 (regulation of glycoslyis) is controlled by which hormones
insulin and glucagon
EXAM QUESTION: Explain the regulation of gluconeogenesis graph of reaction 9 and compare it to reaction 3 of glycolysis
Reaction 9 (gluconeogeneis)NO F26BP = higher vmax faster, but then when present it has a slower Vmax
Reaction 3 (glycolysis): Opposite effect
Explain the regulation of the synthesis and degradation of fructose-2,6-bisphosphate in liver (Exam Question: How can gluconeogeneis and glycolysis be controlled by hormones in reciprocal regulation )
Both occur in the level:
1) Insulin = produced in high glucose levels for storage (high blood sugar eg. After breakfast) = produces cholestrol also when were full = phospho-protein phosphotase (removes phosphate) to make FBPase-2 inactive and PFK-2 active (stimulates glycolysis) = increase F26BP
2) Glucagon = broken down in low glucose levels to increase glucose levels (low blood sugar eg. Starving) = uses PKA which phosphorylates enzyme PFK-2 to become FBPase-2 active (inhibits glycolysis) = decrease F26BP
Reaction 10 glycolysis regulation:
1) Allosteric control of the Pyruvate kinase
2) Inhibited by Acetyl-CoA and by ATP (energy sensor)
3) Activated by fructose-1,6-biphosphate (F1,6 BP) = reaction 3 is pushing forward reaction 10 = positive regulator of pyruvate kinase
Explain inhibition of reaction 10 regulation:
The liver pyruvate kinase is also inactivated by cAMP-dependent phosphorylation
Pyruvate kinase = stimulated by glucagon (phosphorylates pyruvate kinase to inactivate it) = low blood glucose = inhibit glycolysis
Pyruvate kinase can be activated by protein phosphatase (maybe insulin?) = high blood glucose = activates glycolysis
Reaction 1 regulation of gluconeogeneisis
1) Allosteric control of the Pyruvate carboxylase
2) Activated by Acetyl-CoA
Acetyl-CoA acts as a master regulator of (Reaction 1 regulation of gluconeogeneisis)
pyruvates fate:
Positive regulation: Gluconeogenesis for glucose synthesis (glycogen).
Negative regulation: TCA cycle for energy production.
Futile Cycle
a precursor is converted into a product by a forward reaction and then resynthesized to the precursor. In such a reaction, there is no net product accumulation, but energy (ATP) is used
eg. If both glycolysis and gluconeogenesis are both running, you will spend energy doing it because we will use more energy than we make
Homeostatic purpose of the futile concept
- Metabolic idling.
- Can it be a treatment for obesity? You can burn energy and fat potentially by using more energy than making
