Lecture 3.4: Enzyme Inhibition

Question 1

Reversible Inhibitors

Answer 1

associate and dissociate rapidly from enzyme
form NONCOVALENT bonds with their target enzymes

Question 2

irreversible inhibitors

Answer 2

dissociate very slowly
form covalent bonds with their target enzyme
kill the enzyme by tigth binding to the enzyme

Question 3

Sucide Inhibitors

Answer 3

a type of irreversible inhibitor and form a covalent bond with the enzyme that results in irreversible inaction

Question 4

DFP is a [ ] inhibitor, that forms a [ ] bond with reactive [ ] residues and blocks enzymes

Answer 4

irreversible
covalent
serine

Question 5

Competitive inhibition

Answer 5

• binds to free enzyme
• inhibits substrate binding at the active site
• generally non-reactive
• inhibition can be overcome by increasing [S]

Question 6

Competitive inhibition

Affinity of I for E
& Trends

Answer 6

K_I = [E][I]/[EI]
increased Km = decreased affinity
vmax = unaffected
Km shifts RIGHT

Question 7

Uncompetitive inhibitors

Answer 7

• binds at a site distinct from active site
• does not bind to the enzyme but to the Enzyme-substrate complex
• nonproductive ESI is formed
• inhibitions cannot be overcome by increasing [S]

Question 8

uncompetitve inhibition

Affinity of I to ES
& trends

Answer 8

K_I^’ = [ES][I]/[ES]
Km decreases
Vmax decreases
Km shifts LEFT

Question 9

Mixed Inhibitors

Answer 9

• Binds at a site distinct from the active site
• binds to both the E and ES
• Nonproductive ESI is formed
• inhibition cannot be overcome by increasing [S]

Question 10

Mixed inhibitors

Affinity of I for E
& trends

Answer 10

Both K_I values from competitive and uncompetitive
Noncompetitive:
Km = unaffected
Vmax = decreases

Question 11

Km-app increases when K’I [ ] KI

Answer 11

greater than
mimics competitive inhibition

Question 12

Km-app decreases when K’I [ ] KI

Answer 12

less than
mimics uncompetitive inhibition

Question 13

Km-app = Km when K’I [ ] KI

Answer 13

equal to
mimics noncompetitive inhibition