Mechanisms and Inhibitors

Question 1

What are the four catalytic strategies?

Answer 1

1) Covalent catalysis
2) General acid/base catalysis
3) Metal ion catalysis
4) Catalysis by approximation and orientation

Question 2

Covalent Catalysis

Answer 2

The active site contains a reactive group that become covalently modified

Question 3

General Acid-Base Catalysis

Answer 3

A molecule other than water plays the role of a proton acceptor/donor during catalysis

Question 4

Metal Ion Catalysis

Answer 4

Metal ions function catalytically by:

1. Stabilizing a neg charge on a reaction intermed
2. Generating a nucleophile by increasing the acidity of a nearby molecule such as water
3. Increase the binding energy through interaction with the substrate

Question 5

Catalysis by Approximation and Orientation

Answer 5

Two substrates are brought into close proximity and correct orientation when bound to the enzyme

Question 6

What are inhibitors?

Answer 6

Small molecules that inhibit enzyme activity

• Exist in nature (poisons, toxins, regulators)
• Also synthesized by chemists or discovered through screening small molecule libraries
• Can be reversible or irreversible

Question 7

What are the types of reversible enzyme inhibitors?

Answer 7

1) Competitive inhibitor
2) Uncompetitive inhibitor
3) Noncompetitive inhibtor

Question 8

Competitive Inhibition

Answer 8

The inhibitor resembles the substrate and binds to the active site

• As the concentration of inhibitor increases, higher concentrations of substrate are required to obtain a particular velocity
• The inhibitor has no effect on Vmax, but increases Km

Question 9

Uncompetitive Inhibition

Answer 9

The inhibitor binds to the ES complex

• The enzyme-substrate-inhibitor (ESI) complex does not form any product
• Both Km and Vmax decrease

Question 10

Noncompetitive Inhibition

Answer 10

The inhibitor binds to the enzyme alone or the enzyme-inhibitor complex

• The EI and ESI complexes do not form any product
• Vmax decreases and Km is unchanged

Question 11

What are irreversible enzyme inhibitors?

Answer 11

Dissociate very slowly from the enzyme

• Covalently bound or very tight non-covalent binding
• Used to experimentally determine enzyme mechanism

Question 12

What are the types of irreversible inhibitors?

Answer 12

1) Group-specific reagents
2) Affinity labels
3) Suicide inhibitors
4) Transition-state analogs

Question 13

Group Specific Reagents

Answer 13

Modify specific R groups of amino acids

Question 14

Affinity labels

Answer 14

Covalently modify active site residues structurally similar to substrate
(More specific for an enzyme’s active site than group-specific reagents)

Question 15

Suicide Inhibitor

Answer 15

Chemically modified substrate that binds and is initially processed by the enzyme
- Mechanism of catalysis results in chemical reactive intermediate that inactivates the enzyme through covalent modification

Question 16

Transition State Analogs

Answer 16

Molecules that inhibit an enzyme by binding the active site and mimicking the transition state