Enzyme Inhibition

Question 1

It is a molecule that disrupts the normal reaction pathway between an enzyme and a substrate.

It decreases or stops the rate of enzyme-catalyzed reactions.

Answer 1

Enzyme inhibitors.

Question 2

Read: Purpose of Enzyme Inhibitors.

Answer 2

Enzyme inhibitors prevent the formation of an enzyme-substrate complex and hence prevent the formation of product.

It can be competitive or noncompetitive.

Question 3

2 Types of Enzyme Inhibition

Answer 3

1. Reversible Inhibitors

2. Irreversible Inhibitors

Question 4

Read: Normal Enzyme Reaction

Answer 4

• In a normal reaction, a substrate binds to an enzyme (via the active site) to form an enzyme-substrate complex.
• The shape and properties of the substrate and active site are complementary, resulting in enzyme-substrate specificity
• When binding occurs, the active site undergoes a conformational change to optimally interact with the substrate (induced fit)
• This conformational change destabilizes chemical bonds within the substrate, lowering the activation energy
• As a consequence of enzyme interaction, the substrate is converted into product at an accelerated rate

Process:

enzyme + substrate → enzyme-substrate complex → Product(s). Then the substrate that reacts to enzyme will produce products.

Question 5

4 Types of Reversible Inhibition

Answer 5

1. Competitive inhibition
2. Uncompetitive inhibition
3. Noncompetitive inhibition
4. Mixed inhibition

Question 6

Read: Explanation in Competitive inhibition

Answer 6

• Competitive inhibition involves a molecule, other than the substrate, binding to the enzyme’s active site
• The molecule (inhibitor) is structurally and chemically similar to the substrate (hence able to bind to the active site)
• The competitive inhibitor blocks the active site and thus prevents substrate binding
• As the inhibitor is in competition with the substrate, its effects can be reduced by increasing substrate concentration

Process:

enzyme + substrate + inhibitor → enzyme-inhibitor complex → NO REACTION because the inhibitor block the active site.

Question 7

Read: Explanation in Noncompetitive inhibition

Answer 7

• Non-competitive inhibition involves a molecule binding to a site other than the active site (an allosteric site)
• The binding of the inhibitor to the allosteric site causes a conformational change to the enzyme’s active site
• As a result of this change, the active site and substrate no longer share specificity, meaning the substrate cannot bind
• As the inhibitor is not in direct competition with the substrate, increasing substrate levels cannot mitigate the inhibitor’s effect

Process:

enzyme + inhibitor + substrate → enzyme-inhibitor complex → NO REACTION because the enzyme changes it shape that not fit to the substrate.

Question 8

Read: Mixed Inhibition

Answer 8

• Mixed inhibition is when the inhibitor binds to the enzyme at a location distinct from the
substrate binding site.
• Similar to noncompetitive inhibition except that binding of the substrate or the inhibitor affect
the enzyme’s binding affinity for the other.
• Binding affinity for the substrate is decreased when the inhibitor is present.

Process:
Whole reaction:
Enzyme + Substrate → Enzyme substrate → Product
Enzyme + Substrate + Inhibitor → Enzyme-inhibitor-substrate → NO PRODUCT

Question 9

Read: Uncompetitive Inhibition

Answer 9

• Also known as Allosteric inhibition Inhibition of enzyme activity with combining with allosteric site.
• The inhibitor binds ONLY to the enzyme-substrate complex in this process. Binding of the inhibitor prevents the formation of products by causing a change in the interaction between the enzyme and the substrate.

Process:
enzyme + substrate → enzyme-substrate → Product
enzyme + substrate + inhibitors → enzyme-substrate → No reaction