Allosteric regulation

Question 1

Definition of allosteric

Answer 1

Of or involving a change in the shape and activity of an enzyme that results from the binding of a regulatory molecule at a site other than the active site

Question 2

Which steps are allosterically regulated in glycolysis?

Answer 2

The three irreversible steps

Question 3

How is the step glucose -> Glucose-6-phosphate regulated?

Answer 3

Liver =
Isozyme (Enzyme) = Glucokinase
Regulation = Blood glucose needs to be km= 5-10mM (Need high blood glucose for this reaction to occur in the liver)
Muscle =
Isozyme (enzyme) = Hexokinase
Regulation = Blood glucose km = 0.1mM (Don’t need high blood glucose for this reaction to occur). Low km also means a greater binding affinity for substrates binding. Inhibited = High concentration of Glucose-6-phosphate

Question 4

How is the step Fructose-6-phosphate -> Fructose-1,6-Bisphosphate regulated?

Answer 4

Liver =
Isozyme (Enzyme) = Phosphofructokinase -1
Regulation -> Inhibited = ATP, H+, Citrate. Encouraged = AMP, ADP, F-2,6-bisP
Muscle =
Isozyme (Enzyme) = Phosphofructokinase -1
Regulation -> Inhibited = ATP, H+, Citrate. Encouraged = AMP, ADP, F-2,6-bisP

Question 5

How is the step Phosphoenolpyruvate -> Pyruvate regulated?

Answer 5

Liver =
Isozyme (Enzyme) = L-Pyruvate kinase (L-PK exists due to covalent modification.)
Regulation -> Inhibition = ATP, Alanine. Encouraged= F-1,6-bisP
Muscle =
Isozyme (Enzyme) = M-Pyruvate kinase
Regulation -> Inhibition = ATP, Alanine. Encouraged= F-1,6-bisP

Question 6

How can compartmentalisation be used as a form of regulation?

Answer 6

Prevents futile cycling by ensuring reactions occur in different parts of the cell

Question 7

What is meant when enzymes are moved into a relaxed or tensed state?

Answer 7

Allosteric regulators will bind in the same places that aren’t the active site, and when more inhibitors are bound, the enzyme will move into the tensed state, though when activators are bound this moves the enzyme into a relaxed state. These two different allosteric regulators will competitively bind these sites, and so the equilibrium between tensed and relaxed states will depend on all regulators present and the concentrations at which they are present.