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9: Enzyme Allostery

Students analyze allosteric regulation, cooperativity, and sigmoidal binding curves, calculate Hill coefficients from hemoglobin oxygen binding data, and trace end-product feedback control through metabolic pathway diagrams.

LibreTexts reference: Unit 2, Chapter 4: Enzyme Allostery LibreTexts

Allosteric Enzyme Models from Conformational Descriptions

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Allosteric enzymes are regulated by conformational changes between the T (tense, low-affinity) and R (relaxed, high-affinity) states. Two classical models describe how these transitions occur across subunits.
The   model states that all subunits in an allosteric enzyme must be in either the T or the R state; there cannot be hybrids.
Which allosteric model is being described above?

 

Effects on Metabolite Production from Enzyme Inactivation

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A series of enzymes catalyze reactions involving the metabolites in the branched metabolic pathway shown below. The ellipsis (...) indicates that additional upstream steps are not shown.

E1 E2 E3
I → J → K → L ↘
E4 E5 E6
⤚ → Q → R → S
M → N → O → P ↗
E7 E8 E9

If enzyme E1 is completely inactivated, what happens to the production of Q?

 

Determining Enzyme Inhibition Impact on Metabolite Production

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A series of enzymes catalyze reactions involving the metabolites in the branched metabolic pathway shown below. The ellipsis (...) indicates that additional upstream steps are not shown.

E4 E5 E6
↗ E → F → G
E1 E2 E3
··· → A → B → C → D
E7 E8 E9
↘ H → I → J

If enzyme E7 is completely inactivated, what happens to the production of G?

 

Determining Hemoglobin Oxygen Affinity Changes Under Different Conditions

Click to show Determining Hemoglobin Oxygen Affinity Changes Under Different Conditions example problem

Hemoglobin is one of the most heavily modulated proteins in the body. Its oxygen binding affinity is regulated by multiple physiological factors that shift the balance between different conformational states of the protein.
A higher pH of 7.6 has this effect on the normal adult hemoglobin protein:

 

Allosteric Enzymes in Metabolic Pathways

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Allosteric regulation of metabolic pathways:
A series of enzymes catalyze the reactions in the following metabolic pathway:

E1 E2 E3 E4 E5
D → E → F → G → H → I

In a typical metabolic pathway, an allosteric enzyme is sensitive to changes in concentration of specific molecules and can regulate the rate of reactions.
Which one of the enzymes in the metabolic pathway above is most likely to be an allosteric enzyme?

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