L12: Control of Enzyme Activity

Question 1

This is a compound that binds to an enzyme and reduces its activity

Answer 1

Inhibitors

Question 2

What are 4 functions of enzyme inhibitors?

Answer 2

1) regulate metabolism
2) serves as drugs, poisons and toxins
3) used to study enzyme mechanisms
4) used to study metabolic pathways

Question 3

What are the 2 classes of inhibitor? What is their main difference?

Answer 3

Irreversible inhibitor - binds covalently to enzyme

Reversible inhibitor - does not covalently bind to enzyme

Question 4

This type of inhibitor reacts with a specific amino acid side chain and permanently inactivates a part of the enzyme. (maybe the part with the specific amino acid side chain)

Answer 4

Irreversible inhibitor

Question 5

This type of inhibitor leaves the enzyme in its original condition.

Answer 5

Reversible inhibitor

Question 6

What are the 2 types of reversible inhibitors?

Answer 6

Competitive and non-competitive inhibitors

Question 7

What’s the difference between competitive and non-competitive inhibition?

Answer 7

Competitive inhibition - competes directly with substrate for the active site; mutually exclusive (so only the substrate or enzyme can bind at a time)

Non-competitive inhibition - inhibitor binds at a different site than the substrate

• pure non-competitive inhibition means that the binding of inhibitor has no effect on the binding of substrate. Substrate binds to E and EI with the same affinity.

Question 8

How do competitive inhibitors increase Km?

Answer 8

Inhibitor increases Km by increasing the amount of substrate needed to reach Vmax.

• more substrate is needed because there’s competition going on at the active site.

Question 9

What kind of inhibitor is a lipitor?

Answer 9

Competitive inhibitor

Question 10

Anastrozole works as an inhibitor of the enzyme aromastase. But when it acts on the enzyme, more substrate is always needed to reach Vmax. What kind of inhibitor is anastrozole?

Answer 10

Competitive inhibitor

Question 11

What happens to the structure of the active site in pure non-competitive inhibition?

Answer 11

The substrate still binds, but transition state stabilisation is no longer optimal (Because the inhibitor binding to a different site on the enzyme, changes the structure of the active site - but once substrate binds, the inhibitor on the other side blocks its function to prevent it from stabilising the transition state)

Question 12

What’s the difference between pure and mixed non-competitive inhibition? (in terms of kinetics)

Answer 12

Pure = only Vmax changes (because you need to add substrate)

Mixed = Vmax and Km can change

Question 13

What are the 3 common methods of enzyme regulation?

Answer 13

Covalent modification (like phosphorylation)

Allosteric effects

Proteolytic cleavage

Question 14

Why do we need multiple modes of regulation?

Answer 14

For fine control of the enzyme (being able to turn enzyme on and off)

Question 15

True or false. Enzyme activity cannot be modulated.

Answer 15

False. It can be through inhibitors, activators, and PTM.